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broken main bearing end cap


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2 hours ago, hot-growler said:

what about getting a replacement block and reboring to fit my pistons? Are there any differences in 2.5 blocks or are they all the same? my cp is recessed and flat piston faces. Just had head rebuilt too with a light skim as gasket had been blowing slightly.

You have a known quantity with your block and it's block numbers match (I presume) your reg doc and Heritage sheet if you have one. I'd prefer a cap repair (remade cap) every time.

Mick Richards

Edited by Motorsport Mickey
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I'm still baffled as to why it broke, and I don't see how the bearing got misshapen. Is there an explanation?

I have some spare bearing caps should you wish to investigate that route, but as Mick rightly points out will still need a good engineering shop to verify.

There are flat and recessed blocks. Any recessed block in 2 or 2.5 form will interchange. The recessed block has additional casting ribs so is stronger.

Jerry

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I considered just fitting and hoping for the best so i refitted the broken cap and torqued it up and pieces fitted together well. added engineers blue and seemed to turn very easily. shell was fine, no obvious rubbing of the crank

Not going to go down that road cos if it fails under load there'll be a mess. 

Just had crank ground to 10 thou and correct bearings fitted.

 

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Neil may be hitting the nail on the head. If you have installed new shells that are too thick (like 1st under on a std crank, it will put a bending moment on the cap and explains the damage you see on the shell.

Waldi

 

PS: I could buy a very cheap block bored to 2.7 ltr including pistons. It hD no bearing caps. I declined. Not even for free.

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Hardly dare ask...have you fitted these size bearings in the other mains caps ? If so does the crankshaft turn over...at all ?.

Mick Richards 

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Another option: did the thin wall bushes that align cap and block properly fit, no dirt in there?

Probably ok, based on bearing damage. 

Definitely then if the journals are correct diameter.

The crankshaft should rotate freely in oiled shells, without the caps installed,  and gradually get more resistance (but not much) as you turn the 1st, 2nd etc cap. Keep testing and comparing during torqueing. 

Best if you can find the cause first, before any further work or spending starts.

Waldi

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you must find the cause of the bearing misshape before you go in any direction . As asked , just one cap or all ?

Cap round the wrong way ???

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Could it be that the thrust washer, possibly being too tight, sat proud of the mating surface, and when tightening the cap, applied a reverse force into the cap and fractured it?

PS It looks like the jammed thrust washer has created a step for the cap end to break over ? Just a thought 

Another angle, was perhaps the shell was not seated correctly in the cap and was left proud one end. Then maybe the opposing bolt was tightened too far down first not allowing the protruding bearing to seat and jamming it. When the second bolt was tightened the cap cracked over the shell step. This might also account for the severe compression of the bearing shell which could not move?

Over to you my dear Watson!

 

Kevin

Edited by boxofbits
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2 hours ago, hot-growler said:

standards before, 10 thou after. not measured. will get my micrometer out to be sure.

 

How do you plan to measure the bearings ? there is obviously the STD  -10 -20 etc marks on the back of the bearing but trying to measure their thickness with a micrometre is crude and because you are trying to measure differences within 1 thou unlikely to give repeatable figures. Really you need to remove the crank and fit the bearings into the main caps and torque the caps down to the manual figures and then measure the inner dia formed by the bearings.

Mick Richards

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16 minutes ago, Motorsport Mickey said:

How do you plan to measure the bearings ? there is obviously the STD  -10 -20 etc marks on the back of the bearing but trying to measure their thickness with a micrometre is crude and because you are trying to measure differences within 1 thou unlikely to give repeatable figures. Really you need to remove the crank and fit the bearings into the main caps and torque the caps down to the manual figures and then measure the inner dia formed by the bearings.

Mick Richards

Would it not be easier to measure the crank journals with a micrometer to determine their size and then compare ( assuming they are marked correctly) the size marked on the shells?

Would you not also need rounded internal micrometer tips to account for the circular shape of the bearing to get a really accurate internal ID reading ?

Kevin

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1 hour ago, boxofbits said:

Would it not be easier to measure the crank journals with a micrometer to determine their size and then compare ( assuming they are marked correctly) the size marked on the shells?

Would you not also need rounded internal micrometer tips to account for the circular shape of the bearing to get a really accurate internal ID reading ?

Kevin

 Kevin you use a small ball bearing (of known dimension .250 say) on the micrometre anvil (tips) inside radii of the bearing (subtract the amount from the thickness) and the outside anvil fits just fine on the outside radii of the bearing. If you've had a crank regrind it's customary to mike the journals and check them ...NEVER trust a machinist, and compare against workshop manual figures.

Again as outlined above fitting the supplied bearings into the block caps and block itself and torquing them up without a crank in the way not only allows checking the fitted dimension but also allows checking of the "crush " of the bearing into the mains curve of the block, you can also check for out of roundness at the same time.  

Mick Richards

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Kevin,

I did as follows:

1) Measure crank journals with micrometer. Compare with info from bearing supplier.

2) Measure bearing bore without shells installed with bore gauge, fully torqued, which is calibrated on micrometer. They are not very expensive, like 70 euros (Dasqua). Compare with BB values.

3) Measure bore again with shells installed, fully torqued. Mark shells and note their orientation.

4) Deducted 1) from 3) which was an indication if the clearance was in correct area.

5) Installed crack shaft and caps w. shells according BB, using Plastigauge to confirm I had not made an error. Plastigauge readings were very close to calculated clearances. 

6) Out of curiosity I measured the shells to compare to each other. I found the King trimetal were 0.01 mm thinner than Glyco and would result in more than needed radial clearance, so installed Glyco. Bore measurements of all 6 confirmed this (as an average). Best done with a large steel bal to avoid indents in the soft shell (I found un-deep scratches from the bore gauge)

Waldi
 

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5 hours ago, Waldi said:

Kevin,

I did as follows:

1) Measure crank journals with micrometer. Compare with info from bearing supplier.

2) Measure bearing bore without shells installed with bore gauge, fully torqued, which is calibrated on micrometer. They are not very expensive, like 70 euros (Dasqua). Compare with BB values.

3) Measure bore again with shells installed, fully torqued. Mark shells and note their orientation.

4) Deducted 1) from 3) which was an indication if the clearance was in correct area.

5) Installed crack shaft and caps w. shells according BB, using Plastigauge to confirm I had not made an error. Plastigauge readings were very close to calculated clearances. 

6) Out of curiosity I measured the shells to compare to each other. I found the King trimetal were 0.01 mm thinner than Glyco and would result in more than needed radial clearance, so installed Glyco. Bore measurements of all 6 confirmed this (as an average). Best done with a large steel bal to avoid indents in the soft shell (I found un-deep scratches from the bore gauge)

Waldi
 

Morning

I do have a Moore & Wright internal micrometer, but when I checked it doesn't appear to have a balled end on any of the anvils, so I don't see how mine can be used to measure internal radii with accuracy. The above method as followed by Waldi does seem good and watertight without any room for error.

With regard to the original post subject, my point about measuring the journals is that it has not been established whether they are in fact 10 thou undersized, though they probably are. with regard to the bearing measurement, Steve may as well scrap the shell set anyway as they have been subject to damage, so surely no point in measuring them now?

I do think its likely to be an assembly error however in my opinion ( but not necessarily correct). I think the shell was protruding from the block and the cap was bolted down unevenly to one side which jammed the shell in the block and the protrusion both cracked the cap and compressed the shell into the cap when tightened, hence the bellowed effect at its weakest area around the oil hole. More to the point, although the cap could be secured in place in two parts, which carries a risk in itself, without crack testing it's impossible to say whether there are not other hairline cracks within the cap?

I would suggest that the whole block might have to be scrapped unless a new cap is made as per Mick's suggestion.

 

Kevin

Micro 1.JPG

Micro 2.JPG

Edited by boxofbits
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This is the set I have:

https://www.dasqua.co.uk/product/dasqua-precision-dial-bore-gauge-35-160-mm-55100005/

Regarding finding the root cause:

If you measure the old shells you at least know this is or isn’t the problem. 

It takes 1 hr at most to check all 4 installed in the block.

I would buy a new set anyway, unless you have glyco or similar which can be bought per pair.

Waldi

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3 hours ago, Waldi said:

This is the set I have:

https://www.dasqua.co.uk/product/dasqua-precision-dial-bore-gauge-35-160-mm-55100005/

Regarding finding the root cause:

If you measure the old shells you at least know this is or isn’t the problem. 

It takes 1 hr at most to check all 4 installed in the block.

I would buy a new set anyway, unless you have glyco or similar which can be bought per pair.

Waldi

Hi Waldi

The Dasqua set look fine and also have correct tips for measuring bores.

Yes agreed I suppose it’s not going to take long to assemble and check that out in the scheme of things to rule them in or out as the cause.

Hopefully Steve will find a way forward with it!

Regards 

Kevin

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Hi Kevin,

If you can find a bearing cap that has a tight fit after removing say 1,0 mm in the block I would be tempted to use that and machine the bore subsequently.
But it is better t first assess the entire  block condition:
First measure your cylinder bores and bearings bores (including camshaft), if more remedial work is needed consider replacing it.
Good luck,

Waldi

 

 

 

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How strange to read of this mysterious event, in that I've also been suffering from a No.4 main crank bearing  problem.   But different.

I rebuilt the engine, carefully measured the endfloat and fitted thrust washers.    Once back in the car and  attempting to start it, after some turn overs, it refused to turn any more.     A socket on the nose found that it would turn, freely, but only in an arc of about 20 degrees.

Stripping it again, I found the rear thrust washer had escaped around the bearing and jammed in the space between it and the crank collar.      Examining the bearing cap, there was a small, about 4mm chip in the edge which confines the end of the thrust washer, which had allowed the washer to spin.      I'm a pretty careful engine builder and I think I would have spotted that beforehand, so did it happen after I assembled the bearing?   No idea.   The actual main bearing seems unconcerned!

A local workshop has cleaned up the crank, and had the chip welded up, but the post-weld work wasn't very good, and I've been plying fine needle files to get the repair flush.   Reassembly will follow, difficult with fingers crossed!

John

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