TLC for my GTD (rebuild), IT RUNS!

[Toby]

Ok. The I just checked, and the cap is definately on the right way round. I can see the tang marks from its original position. The cap is the only main no4 bearing cap I have so unless the machine shop somehow mixed them up with another block.
Unfortunately I haven't got a plastigauge kit (yes stupid) I can try and find one here in the uk.
I pulled the crank and all bearings and fitted the no4 cap, it seems to fit in a number of positions. I can see the original position of the cap, shown here



It seems that when the cap is torqued down it pushes the crank down on to all the upper bearings.

Plastigauge does not usually come in a kit. It is just a long, thin envelope with a green wax thread inside. You will only need one. It comes in red as well for .002-.006" but you want the green.

What do you mean "it seems to fit in a number of positions"?

If a machine shop had the block, it is possible that they mixed the caps from 2 different blocks. Let then know now since you won't get the cap back if its on another running motor. It is possible that the motor has been line bored sometime in the past with one cap backwards or in the wrong position. I have seen that.

You did not say anything about the parting line with the bearings out. Try swapping the cap 180* and see if it gets better.

[wil892]

Well the cap can sit slightly either side of where it should sit.
I'm not certain, but here in the uk we usually would just find another engine if one required line boring, so I'm pretty sure this is the first time the engine has been open.
The parting line is very minimal I will get a picture as soon as I can tomorrow. Good idea about swapping them over, though I'm starting to think that a trip back to the machine shop is in order. Nothing is ever simple!

[kevinm]

i think line hone cost me 150cdn.. i had the same issue when i got to around 40ftlbs on one of the caps...  and by measuring with an inside mic i was able to tell that a few areas had gone oval... so it does happen. but rare im told.

[Toby]

I think it is more likely that the block is warped. It does not have to be much to bind the crank. I might be tempted to scrape the bearing to get a good fit. I had to do that on a Peugeot diesel I rebuilt. It turned out that one of the caps had been machine backward, so it bound up in the "correct" position.

Try installing the #4 cap on backward and see if the fit is better. You should not be able to catch a fingernail in either direction at the parting line on either side.

[wil892]

I think I might have found the problem. Looks like the cap may have been banged slightly when on the block. One side of the cap seat seems to be indented and I think when the cap gets torqued down it cocks and presses the bearing down to the left. Which the lower bearing would indicate.

Now. Does this scrap the block or could it be repaired? I'm not wanting to place any blame for this as it was probably my fault for keeping the caps screwed into the block.

[Mark(The Miser)UK]

I'll just get in before someone screams scrap the block...

I'd be tempted to use an old fashoned razorblade as a shim

[Toby]

It would be silly to scrap the block when all that it needs is a line bore. It is hard to tell from the picture but it looks like that end of the cap was loose and worked back and forth against the block, wearing both slightly. If I were you (and I am hyper cheap) I might just get that bearing scraped to fit. It is the kind of job old time machinists did all of the time when fitting shafts to babbit bearings. It might be best if you could find a retire machinist to do it for you.

You could theoretically shim the cap but finding shim stock in the sub .003" range might be difficult. The other issue is that if you go even slightly too large you lose the "crush" on the bearing shell and then it will spin under a heavy load destroying the motor.

I think you need to mic the bore with a .0001" inside mic to see how much it is out of round. If it is too small it might be putting too much "crush" on the bearing shell and causing it to ripple and pull away from the bore. One could, given sufficient skill, trim the edge of the bearing at the parting line to gain clearance. BUT you won't have any idea what is happeing until you mic the bores.

[Mark(The Miser)UK]

It would be silly to scrap the block when all that it needs is a line bore. It is hard to tell from the picture but it looks like that end of the cap was loose and worked back and forth against the block, wearing both slightly. If I were you (and I am hyper cheap) I might just get that bearing scraped to fit. It is the kind of job old time machinists did all of the time when fitting shafts to babbit bearings. It might be best if you could find a retire machinist to do it for you.

You could theoretically shim the cap but finding shim stock in the sub .003" range might be difficult. The other issue is that if you go even slightly too large you lose the "crush" on the bearing shell and then it will spin under a heavy load destroying the motor.I think you need to mic the bore with a .0001" inside mic to see how much it is out of round. If it is too small it might be putting too much "crush" on the bearing shell and causing it to ripple and pull away from the bore. One could, given sufficient skill, trim the edge of the bearing at the parting line to gain clearance. BUT you won't have any idea what is happeing until you mic the bores.

I think you are over worrying...
From the Bentley rag mag:
Main bearing clearance: As new 0.6 to 3 thou. Wear limit 6 thou!
Big end from new: 0.6 to 2 thou. Wear limit 5 thou.

Thus with a bearing with no clearance, a razor blade being 2 thou would be perfect. High carbon steel etc...
Interestingly oil flow rate range is up to 10x that of a tight fit engine, on an engine reaching allowable limit. That must give a wide range on oil pressures and so a low tolerance engine also has cooler bearings, and hence can run like an old banger, but keep going

[Toby]

I think you are over worrying...
From the Bentley rag mag:
Main bearing clearance: As new 0.6 to 3 thou. Wear limit 6 thou!
Big end from new: 0.6 to 2 thou. Wear limit 5 thou.

Thus with a bearing with no clearance, a razor blade being 2 thou would be perfect. High carbon steel etc...
Interestingly oil flow rate range is up to 10x that of a tight fit engine, on an engine reaching allowable limit. That must give a wide range on oil pressures and so a low tolerance engine also has cooler bearings, and hence can run like an old banger, but keep going.

I think you need to get your mic calibrated. A razor blade is more like .010" or better. That is a huge amount to add to a bearing bore and you will end up with "full floating" mains.

At .006" bottom end clearance you will end up with audible main knocks. That is way too much clearance to run on a street car. Keeping sufficient oil pressure will also be a problem with a warm engine. At .005" clearance on a rod you will also get a rap big time on start up until the oil pressure comes up and a rap while lifting off of the loud pedal. Oil pressure will also be low.
You can run these kinds of clearances for a while, but probably not long term. The longest I have ever run a motor that loose was about 3000 miles. After that they were someone elses problem.

He needs to mic the bores with a .0001 mic so he knows what is wrong. It takes almost no twist in the block to make your stock clearances go away. A line bore is cheap if that or cap wear are the issues. Scraping the mains is even cheaper. BUT first you need to know what the problem is.

[Mark(The Miser)UK]

I think you are over worrying...
From the Bentley rag mag:
Main bearing clearance: As new 0.6 to 3 thou. Wear limit 6 thou!
Big end from new: 0.6 to 2 thou. Wear limit 5 thou.

Thus with a bearing with no clearance, a razor blade being 2 thou would be perfect. High carbon steel etc...
Interestingly oil flow rate range is up to 10x that of a tight fit engine, on an engine reaching allowable limit. That must give a wide range on oil pressures and so a low tolerance engine also has cooler bearings, and hence can run like an old banger, but keep going.

I think you need to get your mic calibrated. A razor blade is more like .010" or better. That is a huge amount to add to a bearing bore and you will end up with "full floating" mains.

At .006" bottom end clearance you will end up with audible main knocks. That is way too much clearance to run on a street car. Keeping sufficient oil pressure will also be a problem with a warm engine. At .005" clearance on a rod you will also get a rap big time on start up until the oil pressure comes up and a rap while lifting off of the loud pedal. Oil pressure will also be low.
You can run these kinds of clearances for a while, but probably not long term. The longest I have ever run a motor that loose was about 3000 miles. After that they were someone elses problem.

He needs to mic the bores with a .0001 mic so he knows what is wrong. It takes almost no twist in the block to make your stock clearances go away. A line bore is cheap if that or cap wear are the issues. Scraping the mains is even cheaper. BUT first you need to know what the problem is.

Forget line boring.
Toby you're on fire but when you go up against me get your facts right.

Scroll down the page of this link until you find double edged razor blades. Then read off the thickness. I've never shaved with a single edged craft blade, but perhaps you have! I'm willing to bet that full torque will loose another thou or two also...

http://www.emsdiasum.com/microscopy/products/preparation/blades.aspx

[Toby]

Don't be changing your story now: You said a razor blade is .002". Your interwebs site says .004". If you actually mic one it will be bigger than that. They are saying single edge razor blades are .009" which is about 1/2 of what they really are.

[Mark(The Miser)UK]

Don't be changing your story now: You said a razor blade is .002". Your interwebs site says .004". If you actually mic one it will be bigger than that. They are saying single edge razor blades are .009" which is about 1/2 of what they really are.

Looks like you better get a better mic if it always reads high
 Haveing said that, different makers probably use different spec sheeting, which may be useful, see below last para.
 My 'off the head' error, means that the double edged blade is better than I thought. The binding cap may not just be zero, but could possibly be negative. 

All said and done, the proof in the pudding is in the eating, so for the sake of a few penny's [cents] trying a double edged razor as a shim, will either work or not.

They do make good additional shims for injectors, along with pieces of tape measure spring, so they will remain in my toolbox.

[BigVWman]

You could give the razor blades a whirl and plastigauge it, would only cost a few cents as noted above! They also make a product called locksmith shim stock that comes as thin as .001 if you find razor blades are too large. You should be able to find a combo that works.

[Toby]

You are barking up the wrong tree here. Until you know WHY it is binding taking any course of action is likely to result in disaster. Just shimming the cap with a razor blade will result in 2 things: 1) It will likely get the crank to turn freely, and 2) increase the bore size to the point where all of the "crush" that holds the main bearing in the journal will be lost. There will be NOTHING to keep the main bearing from spinning, destroying the block and the crank. Only the "crush" hold an insert bearing, The tab is just to locate the bearing; nothing more.

There are at least 6 possible reasons why the crank binds.
1) the crank itself is bent,
2) the block is twisted a very small amount,
3) the main bearing bore is too small, (possibly due to wear at the parting line)
4) the cap is not seating correctly,
5) the cap is on backward, (I have seen a cap that was marked on the wrong side)
6) the main bearing is is incorrectly sized.

Shimming the cap will cure none of these. What it may well do is to convince you that you have fixed the problem. Then when you put the motor together and in a car, it will last from minutes to hours before it is rendered useless.

Now on the other hand if you fix the problem, (whatever that may be), you should be able to get 100k miles out of that same motor. Take the block and crank to the machine shop and have them figure out the problem. They will have the mics and the know how to FIX the problem.

[Mark(The Miser)UK]

All this doom ad gloom .  The bearing won't spin if the bearing is acting as it should and not binding. Bearing will only spin if it is binding/seizing onto the crank.
It will only do this if it is 1) starved of oil, or
2) not starved of oil supply but too tight to allow enough oil to flow, or
 3) In an extreme case, starvation has led to shell wear to the point that it can fold under the other half, or
4) anything else forgotten.

 If the 'shim' reaches part way into bearing edge, then any crushing by the cap onto the bearing will continue.

Why would it need line boring?
I can't imagine how much that would cost here in the UK, then the bore will be oval, or special components required.

This is not a new engine, so what had the engine been doing previously, other than running? This is surely a recently  introduced problem.
If it was a preexisting issue that was overcome somehow, by some P.O. then again there has been something introduced, possibly by mixing components, or someones overzealous use of an air hammer ratchet thingy.


I would try a paper shim under the one side you believe to be overtightened. Just to see if it works. A dial gauge to check for a bent crank might help reassure you, but I don't think it's the issue