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broken main bearing end cap


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Help.

Think i've seroiusly messed up. decided to fill the crankshaft oilway with as i thought it would ease oil pressure build up but when i tightened the cap down i must have had a hydraulic lock. Thoughjt damage was just to bearing but i have just seen a crack in cap #4.

any advice please. Has anyone got a spare cap they are not using? will it need to be line bored?

bit upset... SteveDSC_0191.thumb.JPG.15c925de92a3e4e9c37c40e6f6deca62.JPG

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That's unusual, on the outside edge of the casting. Are you sure it wasn't there before you tried refitting it ? are there any signs of the crack across the bearing surface or on the other side ? 

I can't decide where you think the hydraulic lock might have been, under the bearing itself ? or oil trapped under the cap bolt when tightening ? neither of them would have caused that stress to cause the crack to form. Roger H will be along in a minute and as an ex aircraft Non destructive tester "he da man" when cracks are to be discussed. 

I suspect that crack may have been there some while and trying to get around it will cause stress in it's own right and not a little cost. 

Option 1) Ignore it

I think the crack was there years ago and likely hasn't moved since. As long as the crank cap torques down correctly the engine will run fine, and if the worst happen you'll have plenty of warning with a large drop in oil pressure, stop and get recovered and then do option 2.

Option 2) Have a steel cap remade and then align bore the bearing housing to suit the block.

Costly £250 - £350 area maybe and requiring an engine out full strip down.  

Mick Richards

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thus is what the shell looks like.

I put a 5 thou o/s thrust washer in and decided i han no end float, so i replaced it with a std one andbolted it down. tried totorque it up but struggled,. was a noise i think that is when it gave way. DSC_0189.thumb.JPG.365f992020388b640fc35ca8e2cfc95b.JPG

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18 minutes ago, hot-growler said:

i may have misaligned something when putting it back together???DSC_0196.thumb.JPG.121136033ed189741ec83ae583912fa4.JPG

Hi Steve,

is that the crack at the 9-o-clock position on the right hand hole.

I take it that the crack did not allow the parts to fall in half.

Could the crack have happened this way - Something pushed the shell further in/around than ideal. This cause the cap to grip it and then nip it tight. 

As you torqued the cap down an unequal force pushed on one side of the bolt head/washer and caused the cracking. Not hydraulics. (perhaps it was DOT5)

Ideally you need a new cap but they look to be 'not available'. Would a 2nd hand cap line-bore OK.?

If the cap is still in one piece then you could simply refit and keep your fingers crossed.  With it torqued down where will it wander off to 

Roger

 

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The cap when bolted up will close all those gaps.
There is a small ‘nip’ across the cap in the block, side to side which locates the caps positively, try fitting the cap alone, no bearing and tighten up 2 pulls a side ... no more on the cap until torqued up. if it torques ok I think it will accept a new bearing ( try swapping one of the others) and retorque it then ...same process.

Mick Richards

Edited by Motorsport Mickey
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No, now I think you are back into option 1... sorry it’s aggravation but I’ve broken many more TR bits. Resign yourself to doing it correctly now as suggested by Neil.

Mick Richards

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You need a good quality engineering firm. Even better if they’ve done it before with auto connections. A steel cap needs making up the same size as the one broken, outside dimensions the same to allow it to ‘nip’ into the block, copy the broken cap. Then they’ll put in a jig borer and align bore it ( alignment bore) to accurately give you a new steel cap that fits into place the same as the others and will carry the bearing.

I see you are in Lancashire but that covers a lot of area, can you give us a more Specific area ? The local TR group will be a good ask first to tell you who can do and if trusted.

Mick Richards

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I understand it is tempting to simply install the cap “as is” because, as Mick says, it will close up. If I were stranded in the middle of nowhere I certainly would and it would not surprise me if it run ok for many years. But given all the effort involve, I would source another cap, have it milled down a bit and then line-bored to the correct diameter. 

Waldi

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East Lancashire, but can travel

 

 

 

14 minutes ago, Motorsport Mickey said:

You need a good quality engineering firm. Even better if they’ve done it before with auto connections. A steel cap needs making up the same size as the one broken, outside dimensions the same to allow it to ‘nip’ into the block, copy the broken cap. Then they’ll put in a jig borer and align bore it ( alignment bore) to accurately give you a new steel cap that fits into place the same as the others and will carry the bearing.

I see you are in Lancashire but that covers a lot of area, can you give us a more Specific area ? The local TR group will be a good ask first to tell you who can do and if trusted.

Mick Richards

 

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Hi Growler, check out your messages, there’s info there for you.

Mick Richards

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Why not a 2nd hand cap? Should be plenty of old 2500 engines about.

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4 minutes ago, John McCormack said:

Why not a 2nd hand cap? Should be plenty of old 2500 engines about.

Second hand caps are a lottery.
Got to be the correct size to fit the machined registers in the block ( they have to ‘nip’ into the correct position, sometimes they’re slightly different), you are not supposed to mix up the original caps or their orientation from original positions because of this. 
Then have to be machined on the mating faces and bore to allow the crank bore diameter to be reclaimed from out of the meat of the existing material.

A steel cap is more easily and reliably made using the existing cap as the template. It has spare material in whatever plane or dia you want to put into it.

Mick Richards

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7 minutes ago, Motorsport Mickey said:

Second hand caps are a lottery.
Got to be the correct size to fit the machined registers in the block ( they have to ‘nip’ into the correct position, sometimes they’re slightly different), you are not supposed to mix up the original caps or their orientation from original positions because of this. 
Then have to be machined on the mating faces and bore to allow the crank bore diameter to be reclaimed from out of the meat of the existing material.

A steel cap is more easily and reliably made using the existing cap as the template. It has spare material in whatever plane or dia you want to put into it.

Mick Richards

Thanks Mick. A good explanation.

Would it be easier to 'fix' a 2nd hand cap to make it fit than make a new one?

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There is a slit in the block that holts the bracket perfect in position.

I call this the register. Many cars have problems there, for example the

2.2 litre Lotus 4 cylinder 4 valve or the Rover V8 and recently I had a TR6

with problems. It seems there occure heavy forces when crank is rotating.

 

I would expect they made the bracket break and so this bracket can not be used any more

although the slit is prefectly pressed together.

 

In Germany Stefan Schamschulla did the job of making a new bracket and line boring.

 

As I heard of several of these repairs failed you should buy a measuring device from China

to check the out of round condition of the hole after repair.

 

Anyway I would do that job before sending the block for expensive repair to check all the bearings first.

And why not, if you can get a block for free, test all the brackets you have to see if you are lucky and one fits.

I would say max tolerance is 3/100mm, what is already pretty close to the play in the bearing, so that will be

the absolute limit.

 

I had a problem with the bolt in that area and material was pressed out 5/100mm in the thread area. I could cure that prefectly with Dremel and a rubber sanding grinder. Ended up at 1/100mm and engine is running strong since years.

 

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There are "pros" and "cons" for a new steel bracket instead using the cast.

As Waldi said the cast one is milled down a little bit to get material to bore out at line broring.

Typical procedure to repair big ends of con rods. They become out of round often.

The disadvantage is that it is still that weak material that broke before.

 

The Rover V8 has steel caps and often problems with the register. They changed to a register at the the full heigt of the bracket and additionally bolt the bracket from the side to press the register together. And from there I heard about the problems line boring when half is aluminium and half is steel.

Steel and cast iron are closer together but there is still a difference. Needs good equipment, patience and skill to end up with a precise round hole there. Question remains is that necessary for a street engine.

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2 hours ago, Motorsport Mickey said:

Second hand caps are a lottery.
Got to be the correct size to fit the machined registers in the block ( they have to ‘nip’ into the correct position, sometimes they’re slightly different), you are not supposed to mix up the original caps or their orientation from original positions because of this. 
Then have to be machined on the mating faces and bore to allow the crank bore diameter to be reclaimed from out of the meat of the existing material.

A steel cap is more easily and reliably made using the existing cap as the template. It has spare material in whatever plane or dia you want to put into it.

Mick Richards

Hi Steve!

There is a company near me that makes crank shaft main bearing end caps for the Bentley boys new and re-con engines, If interested I can supply details? I live near Slough Berks?

Bruce,

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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.

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54 minutes ago, John McCormack said:

Thanks Mick. A good explanation.

Would it be easier to 'fix' a 2nd hand cap to make it fit than make a new one?

No, making a new cap from a billet steel is a known quantity. A good engineering firm will make it and align bore the block all operations are normal engineering practice...meat and drink.

Whereas a second hand cap, could be cracked itself, sometimes only revealed after work has been done on it.

It may not be an acceptable fit inside the block registers...too big no problem...small it's scrap.

The crankshaft half bore may not be placed accurately within the cap...it may be reclaimable ...it may not.

The cap split line may not be at 90 deg to the bore and need remachining to make it so.

The half bore will need dropping back into the cap meat area further weakening the original design of the cap, a new steel cap you can leave extra material there.

etc etc.

A new steel cap well engineered should be indiscernible in engineering performance to the original apart from being obviously a replacement steel cap.

Mick Richards  

 

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