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Engine Specific Info and Questions => IDI Engine => Topic started by: wil892 on September 09, 2011, 04:08:26 pm
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Before I post my main thread showing the rebuilding of my GTD
I have taken the engine out and stripped the head off. Since replacing the cylinder head with new 17,000 miles ago there are now exhaust valve indents on all four pistons.
I am not sure how this is possible as the engine was timed perfectly, confirmed about twice during this 17,000 period, using the correct locking tools.
The indents themselves are not just "kissing", they have made a noticiable circular ridge on all pistons. The head gasket was replaced with a 3 notch, the same as the old one. There are no dents in the lifters or abnormal wear. Also there was an even layer of soot all over each piston so I assume the valves aren't hitting the piston on every stroke.
I have noticed that cylinder 3, which had low compression has more soot in the exhaust port and oil coming from the guide in that port, which would explain my oil consumption. Whether the low compression and oil are due to a bent valve and guide I don't know.
The only thing I can think of is that the new hydraulic lifters didnt bleed down properly when first started up, but that wouldnt explain why its all the exhaust valves.
Anyone seen this before, and why it has happened?
Thanks, will get some pictures up tomorrow
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wrong head gasket?
funky rods? did you spec the piston protrusion?
valve seats sinking?
are you sure it's not just the cast valve indentions in the pistons??
one can hope right??
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Was there carbon buildup in the indents or were they shiny? If they have darkened, it may have been a condition that existed breifly at first startup.....
Did you shave the head?
Ian
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All 4 exhaust valves hitting is a timing issue. Cam retarded.... Or not.
My head does this.
If your cam is set correctly, then the problem likely to be because the valves are not sunk enough in the head, which is the reason VW had the policy of early times when heads were still being manufactured " Heads not skimmable" Is this head skimmed? Because of valve overlap, clash may be unavoidable [my case]
The burrows in the pistons may be less deep than they appear. What makes them look worse is the raised edge around the circumference. Try scraping it off. True clash halts casm and snaps belt...
Why have you taken the head off? Was it just the oil burning?
How low was the compression?
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The head gasket was a elring 3 notch gasket. The piston protrusion was not measured as the original gasket was three notch as well. Its definitely not just cast in. Clear marks and indents on all pistons with little hole bit in the middle of the valve.
There was an even carbon layer on all of the pistons, I didnt see the indents immediatly, but looking closer I did. Then i brushed off the carbon and the indents can be seen clearly.
The head was a new casting (no-name brand probably chinese) that was built with new OEM valvetrain at a respected VW diesel engine shop. The head was supplied to me as brand new, as was timed properly from the beggining with a new Dayco timing belt. I used feeler gauges on the cam lock to ensure it was fully accurate, then rechecked at least two times since fitting the head when trying to sort my injection timing.
I measured the compression on all four on a cold engine, which showed 250psi on all apart from number 3 cylinder which showed 100psi. I believe the tester wasnt showing accurate results because the engine normally wouldnt properly run with these results. However the engine fires easily even with low cranking speeds, it has just been missing on one cylinder when first fired and consuming oil, and also trickles smoke when cold idling.
The engine had a number of oil leaks and I have removed it and taken it apart for a full going over, it will have a new injection pump and the turbo refurbished as well.
I initially thought the low compression on one cylinder was sticking rings but seeing the valve indents it could be a leaking exhaust valve. The bores show clear honing marks and there is little carbon buildup. I will be measuring the bores when I pull the pistons.
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This is very strange. I kind of like your theory about the hydraulic lifters not being drained down before the initial start. The other possibilities could be that the valves are too long (e.g. is it possible to put the keepers on wrong?), the distance between the deck of the head and the cam is too short (e.g. cheap aftermarket head), or the cam is not stock dimensionally (e.g. base circle reduced for higher lift of valves).
However, it seems like the problem has gone away on its own, which goes back to the lifter issue, since none of these other issues can fix themselves. If you had problems initially with the timing, there could have been a lot of banging of pistons and valves going on inside the engine that would have been masked by the sound of an improperly timed pump. That could have been why you never noticed it.
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Well I don't think the keepers can get put on wrong enough to hold the valve different, but either way, the lifter pushes on the tip of the valve and that dimension has to be in a certain range for the lifter to work properly.
Also I believe the book says to squeeze the lifters with a c clamp to make it shorten as much as possible. If that step was skipped then I can see the valves hitting the pistons at first.
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rabbid, the engine was cam to crank timed perfectly before I started it up for the first time with the new head. I did not have a dial indicator at the time so I couldnt set the injection timing.
The engine was started until it fired regularly, which took a few seconds. As I remember there were no banging sounds just lifter ticking as the whole head was new. It was then switched off and towed to the local diesel specialist who set the injection timing to stock. I towed the car home and then started it and it warmed up, then I did the last torque sequence.
I cannot think of a single event when valves hit pistons. And I don't know if at high rpm they have been hitting them all the time. I cant believe the valves haven't broken up in 17,000 with the dents they have made in the pistons. Also the dents have definitly come from this head as they had no marks when I installed the new head.
My bentley manual says leave lifters for 30 minutes to settle after installing to prevent valve contact. It took me at least a few hours to attach everything again and then start it. In fact I think I left it overnight after installing the head until starting.
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How about weak exhaust valve springs? Maybe they're floating a little at higher RPMs? And these engines are so loud at high RPMs anyway, it might be kind of hard to notice. It might also explain why the engine started ok the first time you fired it up. If there really had been bad piston/valve clearance issues, it could have got bound up when you first cranked it.
Don't these engines use 2 springs (inner and outer) for the valves? Maybe you're missing some springs? Intake valve springs could be weak too, but they wouldn't be a problem in this case since the piston's low in the cylinder when the intake valve closes.
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How about weak exhaust valve springs? Maybe they're floating a little at higher RPMs? And these engines are so loud at high RPMs anyway, it might be kind of hard to notice. It might also explain why the engine started ok the first time you fired it up. If there really had been bad piston/valve clearance issues, it could have got bound up when you first cranked it.
Don't these engines use 2 springs (inner and outer) for the valves? Maybe you're missing some springs? Intake valve springs could be weak too, but they wouldn't be a problem in this case since the piston's low in the cylinder when the intake valve closes.
Yup
I don't think it would run very good if the valves were floating.
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Ok, here are some pictures. Just to say I don't think the valves were floating as the engine used to pull really well above 4000 rpm but was quite smokey.
The state of the conrod shells is bad, compared to the mains which have only slight wear.
(http://i260.photobucket.com/albums/ii36/wil892/P9103397.jpg)
(http://i260.photobucket.com/albums/ii36/wil892/P9103399.jpg)
(http://i260.photobucket.com/albums/ii36/wil892/P9103404.jpg)
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Just to say I don't think the valves were floating as the engine used to pull really well above 4000 rpm but was quite smokey.
So because the engine pulls well above 4000 RPM means the valves weren't floating at 5000 RPM? I'm just suggesting ideas here, but you've pretty much shot everything down without even checking. It sounds like you're looking for a silver bullet, but I think if there was one, someone would have suggested it by now. Figuring out why your valves made contact with your pistons is going to take some time, and require that you check a few things.
I would suggest removing the cam and lifters to make sure both sets of springs are there. How hard are they to press down? It should be pretty hard. Make sure the valves are actually opening when you do this, and that it's not just the lifters giving. Have you checked the length of the valves?
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So you've taken the engine apart now, probably needlessly. Those impressions are historic, and likely trivial, although naturally alarming to many. The reason I cn say they are historic, is because of the carbon granules and the lack of concentric circles.
Here is a picture of on going clash:
http://imageshack.us/photo/my-images/844/imgp9926.jpg/
& one of its sisters
http://imageshack.us/photo/my-images/26/imgp9923.jpg/
Note those circles I mentioned. They are there because 1000's of hits by the corroded exhaust valve as it rotates.
Also note the shadow of the inlet valve on the second piston. Meaning I have nowhere to go.
This is my engine, and it is still running and getting 50 to 60 mpg [uk] 8)
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Mark thanks for the info about the concentric circles, that makes sense to me.
I really don't think I took the engine apart needlessly though. There is some conserable wear on the connecting rod bearings and compression is low on number three cylinder (hence me taking the thing apart). There is oil everywhere from failing seals (crankshaft). I was getting 40-45 mpg.
I can only think number three has low compression due to a slight valve leak caused by piston contact. I can see an oil trail coming from the guide in the exhaust port on number three as well.
Rabbid, sorry if you think i'm dismissing everything, I have simply answered all the questions accurately with the procedure I took. I didnt mean to sound like I dismissed your suggestion because I haven't. This new head cost me a lot of money a couple of years ago and to find it needs looking at and probably the exhaust valves replacing already, is quite annoying, as I did everything exactly to the book and bought all the correct tooling.
I will check the valves when I can get the head dismantled (I have no valve compressor), but I did try and push the lifters down but couldn't with any of them, even with a lot of force.
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"Needlessly" was a little excessive ;D
Looking at the carbon swirls across the pistons, I'd say that the injectors were very well matched. I'd also say that compression was good too, or at least doing an 'equal job'.
The shell bearings are not bad either :o I know they have, a few burnish markings, and one has a minor flake of something. However, I don't suppose their depth/thickness has changed, and they are merely reflecting slight imperfections in con rods etc; and are simply snuggling themselves into their location.
Possibly the best pictures of shell bearing wear and it's causes can be found on the 'Clevite' site.
As long as you give the oil pump an overhaul, I'd leave those bearings alone. A new bearing still has to bed in, if there are any slight anomalies and engines do have plenty of those.
Much variation in compression ratio can be down to differing levels of ring gap alignment.
Best initial setting for ring gaps is not the 120 deg apart put in books but 180 degrees for the top two rings and about 175 degrees for the oil ring.
As you have ther head off, to check the seating of the valves, invert the head and pour some kerosine onto the closed valve heads...Oops paraffin ;D
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Ok, I had a chance to compare this head with my old head (which is genuine). It looks like the exhaust valves are a lot closer to the cylinder head face than my old genuine head. They really are almost level with the face of the head whereas the old genuine head has its exhaust valves sunken further into the head with a greater distance between the face.
I think i'm going to take the head to where I got it to have it checked out and just see what they say about it. I have no technical experience with cylinder head building so not really in the best of positions to point the finger.
While the head has worked, I think i'm going to try and find a decent genuine one that I can get built up, as this has kind of shown me why these "chinese" cylinder heads haven't the best name.
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Ok, spoke to the place who originally built the head. They are very helpful but are blaming it on incorrect timing, which is fair enough as it must happen quite a lot.
HOWEVER, I know for a fact this engine has always had correct timing, so I believe the head is still to blame.
Is there a minimum valve recession spec that is required in these engines? Doing a search I have found there is obviously a maximum, but no minimum.
Basically the exhaust valves are showing next to no recession from the cylinder head surface, while the inlets show visible recession as on my old head.
There is no camshaft installed so all valves are fully seated.
I have not had the chance to measure the recession but I'm not joking, the exhaust valves can practically be seen if i look at the head surface horizontally, which just doesnt seem right.
If I can sort out some information and measure the recessions I will get in touch with the shop again to see what they say.
Would this minimal amount of recession lead to valve piston contact at higher rpm?
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The valves are recessed some as you suggest. I do remember reading somewhere that if machining of the head surface is needed, a max of .005" can be taken off. So the valves will still be recessed. Can you measure the depth of recess and see if a 3 notch mls gasket will make up the difference? If the head has been working fine otherwise can you makeup the difference with a thicker head gasket? If not a vw head is the only option...$.02
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sounds like they shaved it too much.
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The valves are recessed some as you suggest. I do remember reading somewhere that if machining of the head surface is needed, a max of .005" can be taken off. So the valves will still be recessed. Can you measure the depth of recess and see if a 3 notch mls gasket will make up the difference? If the head has been working fine otherwise can you makeup the difference with a thicker head gasket? If not a vw head is the only option...$.02
Measure yours against specification.
IME thicker gasket just doesn't run the same.
You can get the seats and or valves cut down on any head.
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The valves are recessed some as you suggest. I do remember reading somewhere that if machining of the head surface is needed, a max of .005" can be taken off. So the valves will still be recessed. Can you measure the depth of recess and see if a 3 notch mls gasket will make up the difference? If the head has been working fine otherwise can you makeup the difference with a thicker head gasket? If not a vw head is the only option...$.02
Measure yours against specification.
IME thicker gasket just doesn't run the same.
You can get the seats and or valves cut down on any head.
that is the best solution, shouldn't cost much either, well a new head is the best option.
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From the bentley: surface of head to valve face, Maximum = 1.5mm and minimum = .5mm.
Sounds like they have to redo it. Everyone knows that on these engines the valves get close to the pistons all the time, having the valves start out even closer is a really good way to make it interfere during operation.
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i guess they shaved the head even tho it was brand new? a lot of machine shops will skim every head that comes in, which is fine on gas engines where they just straighten them up to make sure the customer doesn't come back to them, but on these engines, it really should only be done out of necessity, i had an excellent condition used head, it doesn't even have cracks between the valves, i didn't tell the machine shop i had rebuild it not to shave they head, and they did, this head was so straight it was crazy... ugh i know for next time tho to tell them not to.
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i guess they shaved the head even tho it was brand new?
I'd not be surprised if ChinaHead didn't put the seats at the right depth to start, or got a batch of thicker valves.
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From the bentley: surface of head to valve face, Maximum = 1.5mm and minimum = .5mm.Sounds like they have to redo it. Everyone knows that on these engines the valves get close to the pistons all the time, having the valves start out even closer is a really good way to make it interfere during operation.
Are you sure your Bentley says that? Read again, and I think that youwill find that the 'd' =0.5mm is for a different diagram.
That is how it is for my 1985 Quantum Bentley. As far as I'm concerned that 'maximum' is an error, or at least it should also be linked to a minimum.
The 0.5mm is referring to the minimum thickness of the edge of the valve.
It is typical of the Bentley 'rag-mags'. They merely copied the same omission from the VAG. official mag. A lesson in plagerism if ever there was one ::)
VAG was only interested in the 1980's in the sale of new heads, hence the "Heads cannot be skimmed" proclamation.
It was of course a lie. Bulletin #4 in the VAG mag may contain ther truth, but alas someone took the info out of my copy before selling me it! My engine is living proof of the ability to skim and of going beyond the limit. ;D
However, assuming the valve seat hasn't sunk into the head, then if someone has the thickness of a new valve, the original depth can be found,; eg if original valves are 2mm thick, then they are flush :o
If aftermarket valves are thicker than true OEM, then skimming valve face is in order. This is my next move when I take the head off, Not doing it until I need to though
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i guess they shaved the head even tho it was brand new?
I'd not be surprised if ChinaHead didn't put the seats at the right depth to start, or got a batch of thicker valves.
I didn't see this post as I started writing my post 7 hours ago and got called away ;D
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Are you sure your Bentley says that? Read again, and I think that you will find that the 'd' =0.5mm is for a different diagram.
I just checked again and I'm 100% sure that what it means.
I'll take a picture of the diagram and wording and post it in the next day or two.
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This is what I have:
1982 to 1985 Quantum Bentley both 'd's on one page but under 2 diagrams
(http://img198.imageshack.us/img198/8040/96722856.jpg) (http://imageshack.us/photo/my-images/198/96722856.jpg/)
Source of depth 'd' Golf 1.6TD VAG manual 1982.
(http://img546.imageshack.us/img546/7805/vag1982maximumdepthofva.jpg) (http://imageshack.us/photo/my-images/546/vag1982maximumdepthofva.jpg/)
Source of valve thickness 'd' Golf1.6TD VAG manual 1982.(http://img849.imageshack.us/img849/7471/21894863.jpg) (http://imageshack.us/photo/my-images/849/21894863.jpg/)
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Sorry those pictures aren't the best and the Image Host is not giving me the usual A3 sized picture.
Useing 'control and scroll' on your mouse together should enlarge the pics enough to see[color] that fig 17 and 16 in the Quantum Bentley are merely reversed order Fig6 and Fig7 in the earlier Golf VAG workshop mag, but each still has it's own 'd'
If the Golf Bentley omits the valve edge photo but still prints the quote, then it's another nail in the coffin of your Bentley bibles ::)
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If it were me, i'd probably replace those rode bearings and forget about the valve marks.... seen a lot worse :-)
Sadly, i think i've only ever seen one IDI diesel without some valve marks in the pistons!
As has been covered, the big thing if the head has been skimmed is to make sure the valve seat is cut and that the valve is cut back also (i think it was 'b' in those scans). The valve length should be cut back the same amount as the valve seat, otherwise the valve lift will be more than it should be, at all cam positions, hence the marks in the pistons.
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If it were me, i'd probably replace those rode bearings and forget about the valve marks.... seen a lot worse :-)
Sadly, i think i've only ever seen one IDI diesel without some valve marks in the pistons!
As has been covered, the big thing if the head has been skimmed is to make sure the valve seat is cut and that the valve is cut back also (i think it was 'b' in those scans). The valve length should be cut back the same amount as the valve seat, otherwise the valve lift will be more than it should be, at all cam positions, hence the marks in the pistons.
Same amount off the valve stems assuming shim gaps correct in the first place and not near bottoming out
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Sick and tired of trying to silence the apparent piston to valve tick from the last 3 years or so. Reset the cam to standard, and measured cam advance, using the 'recommended by Fatmobile' technique of locking cam and reading off flywheel error...
I have been running my cam advanced by3 1/2 teeth on the flywheel, or 2.73deg x 3 1/2 or advanced by 9.5 degrees of crank :o4 3/4 degrees on cam!
Ticking still there but engine now running smoother which is partly down to injectors settling in after a rebuild. Ticking still there with engine switched off and going down an incline in gear. Any ideas what it could be?
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Sick and tired of trying to silence the apparent piston to valve tick from the last 3 years or so. Reset the cam to standard, and measured cam advance, using the 'recommended by Fatmobile' technique of locking cam and reading off flywheel error...
I have been running my cam advanced by3 1/2 teeth on the flywheel, or 2.73deg x 3 1/2 or advanced by 9.5 degrees of crank :o4 3/4 degrees on cam!
Ticking still there but engine now running smoother which is partly down to injectors settling in after a rebuild. Ticking still there with engine switched off and going down an incline in gear. Any ideas what it could be?
Man that's messed up!! What was the cause of this?
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Sick and tired of trying to silence the apparent piston to valve tick from the last 3 years or so. Reset the cam to standard, and measured cam advance, using the 'recommended by Fatmobile' technique of locking cam and reading off flywheel error...
I have been running my cam advanced by3 1/2 teeth on the flywheel, or 2.73deg x 3 1/2 or advanced by 9.5 degrees of crank :o4 3/4 degrees on cam!
Ticking still there but engine now running smoother which is partly down to injectors settling in after a rebuild. Ticking still there with engine switched off and going down an incline in gear. Any ideas what it could be?
Man that's messed up!! What was the cause of this?
I'd just like to add, that it was me who created that humungus timing anomaly. I had done it in about 3 stages in an attempt to alleviate my perceived piston to valve kissing.
My results were somewhat inconclusive, which is disappointing >:(.
Now I've just this week gone back to cam locked at TDC, ticking still there but engine running slightly smoother.
It's not excessive shim gaps, as they are mostly tighter than spec, or in lower region of the range. Oil supply squelches out onto cam with mere hand cranking.
On doing a rering last year, I could not find any play in small ends or big ends.[I'd actually bought new bearings for the purpose.]
I didn't check crank bearings other than side to side float, which was minimal.
I'll just live with it until a problem develops. ;D
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Are you sure your Bentley says that? Read again, and I think that you will find that the 'd' =0.5mm is for a different diagram.
I just checked again and I'm 100% sure that what it means.
I'll take a picture of the diagram and wording and post it in the next day or two.
Candyman, Candyman where are you?
Oops I mean Rabbitman ;D
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Oops, it's kinda rare for me, the bentley, my camera, the camera cord and a computer to all be in the same place at once.
From the '85-'92 Bentley Manual.
(http://i249.photobucket.com/albums/gg218/rabbitdude82/P1010699.jpg)
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Thats just what I'm looking for, thanks rabbitman. I will measure the current distance, which I am almost certain is less than 0.5mm and will post the findings here. If it is less than 0.5mm surely the shop who built the head has something to answer for. I will tackle that when I have some hard evidence though!
Thanks
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in that case, you should get a new head or head rebuild out of them, new pistons, new rod bearings, rodbearings, head gasket, head bolts. but if the valves are already level with the deck, the head has probably been skimmed too far and they owe you a new one.
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Oops, it's kinda rare for me, the bentley, my camera, the camera cord and a computer to all be in the same place at once.
From the '85-'92 Bentley Manual.
(http://i249.photobucket.com/albums/gg218/rabbitdude82/P1010699.jpg)
Excellent, that kind of makes sense.
Did Bentley drop the next picture of the 'd' on the valve thickness?
Does your copy cover the last of the mechanical heads too, which is what my manuals are covering?Bentley have earned themselves a Ranger badge
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Hi
Got an update on this. I checked my Bentley and sure enough it specs the minimum recession of the valve face from cylinder head face as 0.5mm.
So I cleaned up the head and measured the distances of all the valves with the dial gauge.
Inlet valves are recessed between 0.5mm and 0.6mm
Exhaust valves are recessed between 0.15mm and 0.21mm!!!
The head was a new cast and was sold to me as brand new with new valve train parts, so surely this head has been sold with a fairly major flaw. Would these measurements indicate that valve contact could have occured due to mis preparation of the cylinder head?
On another note, one of my prechambers has a crack after 18,000 miles, and the prechambers have created a pretty big ridge in the combustion chamber as if they are pushing their way out.
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I'd bring it back to the guy and tell him you want a new head. To be a sold an out of spec NEW head is pretty low.
I doubt you can get anything done about the prechambers though, they'd say you timed it wrong or something but I'd sure try.
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sounds like a crap head all around. definitely the heads fault :o :o :o
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One more update, and a question!
After seeing the state of the non genuine head I decided to buy a genuine one. Today it turned up, no cracks between valves but same cracks in pre chambers that prompted me to buy a new head a couple of years ago. I've taken some close up shots, do these look in pretty poor shape or is that what happens to these heads? It seems both GTD heads I have had now had these cracks in.
Cylinder 1:
(http://i260.photobucket.com/albums/ii36/wil892/4cadc0ee.jpg)
Cylinder 2:
(http://i260.photobucket.com/albums/ii36/wil892/7bc52ace.jpg)
Cylinder 3:
(http://i260.photobucket.com/albums/ii36/wil892/e7f17759.jpg)
Cylinder 4:
(http://i260.photobucket.com/albums/ii36/wil892/5e763b25.jpg)
I don't seem to have much luck with these 1.6td heads, but luckily this one was too cheap to miss.
Will
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I don't think I'd run it like that, too big of risk.