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Engine Specific Info and Questions => IDI Engine => Topic started by: belchfire on August 25, 2008, 09:32:56 am
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The bypass hose blew on my 1.6 TD and I fried the head into oblivion.
Bought a new one and used my old valves (ground and checked for concentricity), and cam. I installed new hydraulic lifters as the old ones clattered a bit. Timed everything and fired it up. Ran kind of funky due to air & veg oil but then cleared up. All of a sudden an unhappy sound appeared and I shut it down. Inspection revealed that 7 out of 8 lifters had shattered. I could not get the cam gear off so I had to cut the belt cover plate and pull it out. It seems that the gear had slipped on the taper and threw out the timing causing the pistons to smack the valves and break the lifters. I removed the broken ones and was able to salvage the bores with a bearing scraper. I used a puller to remove the pulley and it came off with a bang. It appears that they had friction welded themselves together. I reassembled everything and timed the cam. I then disassembled it removing the cam through the slot I cut. I carefully removed the bolt and installed a dutch key between the shaft and gear. Everything is back together and seems to be working. I've got smoke issues so I think that's IP timing.
So here's the deal. Has anyone had this problem? I do not like the idea of a gear being held in position merely by a taper especially when there's a key slot in the shaft. Is the timing that critical that it has to be within a half of a degree? Seems that every other engine runs perfectly fine being within a degree or two. Yes, I did tighten the bolt to 33 ft/lb and I have done cam timing on race engines. It seems that the valves are ok, I hope.
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My experience has been that when you install a new belt, you are looking at up to half a tooth - that's more than a degree.
Here's the rhetorical question back - The crank cog is the only one with a fixed location. The IP and cam cogs were designed to be adjustable. So, if you wanted to fix the cam, where would you fix it? Also, have you tried to slip a new belt on with the cog not loose and the cam locked into position ? It puts quite a bit of stress on things.
On the other hand, I had a 1.6 blow a cheap Miejer's oil filter and the idiot light was out.... it stopped running, but when I put a new filter on and new oil, it ran for another 50K miles ! Sorry about you luck.
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So did you pull the head a second time and make sure the valves weren't bent?
Did you clean the taper on the cam and gear? I usually overtighten that bolt on purpose, 33 sems to low
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I never have had a problem with the taper holding the cam gear. Never.
There is a little punch hole in the back cover. Your supposed to put a small drift through the hole and smack it sharply with a hammer. On the older ones with out the back cover, its a good wack with a copper mallet, and off it comes. Maybe the uneven sudden pressure distorts the whole pully enough to make it release. But I've never had a problem getting a pulley off that way.
Make sure the taper in the pully and on the cam are squeky clean and torq it tight.
If you haven't pulled the head after the lifters were broken, you have to pull the head to see how many valves bent.
How do you fry the head by blowing the bypass hose?
What is a Dutch key?
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I believe that running with a key on the cam will earn you the ability to buy much more replacement parts than just the valves, guides, and stem seals.
The interference fit has provided literally millions of miles of travel in many of these engines. I'm thinkng there was some other problem which contributed to the demise.
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My opinion would be that the IP and the cam sprocket have to be very closely aligned... to within one tooth... when the belt is at the exact right tension. In order for this to happen something else has to be slightly movable.... namely the cam sprocket.
At least for me, I find that I can't get the timing belt aligned to the right teeth *and* the right tension without the cam sprocket being free to rotate.
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Let me try to work through your replies one at a time. First, when the bypass hose blew, the coolant went bye bye and it turned into a very inefficient air cooled motor. I was doing 80 at the time. Second, a dutch key is created by drilling and tapping a hole where 1/2 is in the shaft and 1/2 is in the gear. A set screw is inserted and viola, a key.
It fired up after installing the old lifters and polishing a few dings on the cam. I fought with the timing for an hour and got it dead nuts.
I took it on the road and the cloud of smoke is still there. I think that my injectors have died. I did a compression test with a home made tester and it said 175-200 psi. I' not sure that my gauge is good. anyway, I pulled the head. There are no marks on any piston!! I will pull the valves and check them but they look good.
I know that VW has logged millions of miles with a tapered fit but the tell tale gall on the gear leads me to believe that there was slippage. 33 ft/lb was straight from the book. Might have gotten some grease from the seal on it.
As for the timing, if the crank and IP are locked, then slack will be taken up by cam gear rotation (no locking bar). the groove looks reasonably horizontal so it's not off that much. 1 tooth is about 13 deg and that can throw things off quite a bit but I don't think that this slight of adjustment isn't that critical. If so, I can remove the key and go back to the taper. Maybe lock tite.
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OK, I was thinking the bypass hose was the hose that went from the god auwful blow off valve to intake. 'I blew a coolant hose' would have been clearer. Which one is the 'bypass hose'?
I'm with libbybapa, 33 ftlbs is not enough, and probably twice that is ok. I'm predisposed to reach for a torque wrench. But on the cam pully, I'm more concerned with the sprocket not moving while its being tightened so I focus more on the wrenches. I'm also a two feeler gauges under the cam lock proponent.
I snug the cam bolt with the cam lock plate and feeler gauges in, then pull them out and go for the big reef. I use a sprocket holder and short breaker bar and reef on it till I'm fairly tensed up. (I'm probably over 66 ftlbs.) Twice around with the crank, then back in with the cam lock and feeler gauges again. If its right, cool. If it off, off comes the cam sprocket and start over.
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Even at 66 ft lb I doun't think I'd be happy if there was grease between the cog and the cam tapper.
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Squeeky clean, bone dry, with brake clean, both the taper on the cam, and the inside of the pully
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more than likely the cam slipped on the sprocket when the lifters self destructed .
i've never seen a stock engine with a tapered cam / sprocket slip if it was put together right ...... ( dodge uses a similar setup on many of it's engines . )
that said i wipe everything down with laquer thinner , then i use a few drops of red locktite on the taper , and bolt holding the sprocket ......
the problem with a dutch key is , what if it doesn't line up the next time the engine is taken apart / worked on ... this is very possible , and more than likely the reason vw didn't use a keyway on the cam on most of it's diesel engines .
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I wouldn`t use locktite on the taper. Just metal on metal.
It`s all every big drill press uses, and they have a hell of a lot more torque than what is being transfered to the cam pulley
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I wouldn`t use locktite on the taper. Just metal on metal.
It`s all every big drill press uses, and they have a hell of a lot more torque than what is being transfered to the cam pulley
i agree
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This country was built on Bridgeports with the Morse taper. I trust a clean tapered fitting any day.
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Never had a sprocket slip either. Always dry surfaces. Sometimes use scouring powder to clean. I can tell if things are right by a gentle nipping up of the bolt and checking to see how well the sprocket begins to adhere. I have a beautiful Snapon torque wrench, but admittedly I've never used it on those bolts. I probably get it somewhere close to the book spec.
What is the strength of a bolt that allows twice spec to be applied?
[Andrew restate that hammer tap procedure. It just struck me that if the bolt is tapped then theory makes me wonder that if the bolt was a tight fit then it is moving the cam away from sprocket...Nah I'll leave that thought in, but the ability to tighten bolts with fingers straight away disproves my idea.]
It IMO will never slip unless it comes across a problem. Ie cam seized due to oil starvation. or crank pulley slippage. Maybe if the cam wedges due to lifter-valve- piston marrage then belt would snap first? Very hard to say. I think unless bolt undoes itself; catastrophic slippage is always a secondary event.
What is the best kind of failure to have??
Ie whose engine rises out of the ashes?
I guess one that only kills one piston's worth of machinery...
At #1 TDC only one valve open, and only partly. would a clash push cam round slightly and then back with the other pistons and so on until engine quickly stoppped?
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Hmm, never thought of that..
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Exactly... nice attempt at a pic, but couldnt you have made it slightly 3 dimensional with a semi translucent rear area depicting the first lobe on the cam rather than the blue crocodile eating a swivvle chair. :shock: :mrgreen:
[Andrew restate that hammer tap procedure. It just struck me that if the bolt is tapped then theory makes me wonder that if the bolt was a tight fit then it is moving the cam away from sprocket...Nah I'll leave that thought in, but the ability to tighten bolts with fingers straight away disproves my idea.]
When a bolt is tightened, the threads of the bolt are not a perfect fit to the threads of the hole. Once the bolt head comes into contact with something, in this case the cam, that something pushes the bolt away from the hole it is threading into. The slight difference in thread sizes, between the bolt and hole, means that there will be a sight space between each of the threads, in the direction of the hole:
(http://i13.photobucket.com/albums/a269/libbybapa/Taper_0001.jpg)
Tapping the bolt will apply force to move the sprocket further onto the shaft. It works for me.
Andrew
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My perception of bolt torque was that it was the tightest that a fastener could be tweaked before it reached the yield point. In theory, if you torque the cam bolt past 33 ft/lb then it would stretch and actually be weaker. The only way to increase the torque is to use a larger bolt or a higher grade. Still, the cam does have a keyway...
Turns out that I did bend one of the intake valves and doncha know, It's apparently a rare gold plated titanium 3 groove type that had to be ordered.
Cost $31 bucks! Glad it's only one. Hope to have it running next weekend.
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My perception of bolt torque was that it was the tightest that a fastener could be tweaked before it reached the yield point. In theory, if you torque the cam bolt past 33 ft/lb then it would stretch and actually be weaker. The only way to increase the torque is to use a larger bolt or a higher grade. Still, the cam does have a keyway...
Sure... except that the same grade bolts can be used for a variety of torques.
My donor-Rabbit's oil pan had grade 12 bolts all the way around, but I can guarantee that they weren't anywhere close to their yield strength even if overtorqued.
Fastener torque specs simply indicate the amount of turning force necessary to put the desired preload on the bolt, to give a desired amount of clamping force.
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It's true that you could tighten a high grade bolt to a lesser value and thus achieve a certain clamping force but why spend the extra money for a better bolt than you need? While engineers will err on the side of a higher safety margin, the bean counters will cut wherever they can. I've gone round and round on the subaru forum as to why my impreza takes 4 1/2 quarts of oil leaving me with a 1/2 quart on the shelf instead of making a slightly bigger oil filter that it so desperately needs. Bean counters figured that saving 1/2 quart per car would add up to millions in their pockets.
I would surmise that the choice of fastener is dependent upon space considerations, number required, and clamping force needed. If a grade 3 is sufficient for an oil pan, then 12's are a waste of money. I wonder if someone replaced your bolts either because they were available or the originals snapped when someone was trying to get a leak stopped.
:arrow: Back to the subject:
The engine is back together and I took it for a run. Seems to be OK other than the old lifters rattling until warm like they did before.
Replaced the injectors and it starts a little harder. I think pump timing will be next.
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I am going to post this reply on the other topic "new cylinder head" as well. libbybapa was right. After checking that the IP wasn't 180 deg out I pulled the head. I could see where bad IP timing would cause it to run poorly but it has nothing to do with compression. Both heads appear identical so I installed an injector and glow plug in the old one and CC'd the pre-chambers. Original german head = 11cc. New head = 13.5cc. Hammered out the inserts. Maybe not the best idea, but I was pissed.
The new insert is about .020" larger in dia. and .007 longer than OEM.
I cc'd them both and amazingly, they were 3cc's each. I then cc'd the spherical chamber up to the edge of the insert boss and that's where the difference was.
How to fix this: I could calculate the volume of the head gasket and get a thinner one. Problem is that I'm already using a 1 notch gasket.
(B) Can't mill the head as the valves are flat on the surface and the chamber's opening would be altered.
(C) Mill the block (also known as a complete tear down) to raise the piston height, however, the amount milled might make the pistons hit the head/valves.
So my real choices are to (A) spend another $500 on a non Chinese head after dumping a grand and a month's worth of work on it or (B)-
Sell the whole thing as-is and get something else non VW. :cry: :cry: :cry:
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you got 265psi consistently across cylinders?
can you measure piston protrusion?
that is very weird, guys that make the 1.6/1.9 franken should have the same problems because of the low compression, but they don't. why?
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I don't know about the 1.6/1.9 franken engines, but if it's a 1.9 block then the larger displacement would take care of a larger chamber volume.
Come to think of it, maybe that's what's going on. If I got a 1.9 short block then maybe this head would work.
As for starting. I can get it started but I have to put the pedal down and let it smoke to high heaven then go. It runs rough & dirty until I get into a good boost then it clears out. It's clearly a compression thing.
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My car has 250 psi and starts up great everytime, even now that it is getting close to freezing. I doubt it will last me the winter, but I'm too broke to buy a new motor right now so I have to keep milking this one.
I think you have a different problem then compression
My starter is not very healthy, battery is fair. Pump is freshly rebuilt and so are the injectors.