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mrfirepro

Big End Bearing - Is This A Problem?

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mrfirepro

The Haynes rebuild manual says that no actual values are given but they suggest 0.025 - 0.050mm

 

1,2 & 4 are all around 0.038mm

 

but No. 3 is 0.076mm

 

Is No. 3 acceptable?

 

If not, do I just use oversized shells is No. 3 bearing & are shells available in such small increments?

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mrfirepro

Just read my post, sorry it didn't make sense should have said what the measurements were for.

 

Those measurements are the clearance tolerances.

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welshpug

is that on a new bearing and does the crank still look good?

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mrfirepro

new bearings and the crank looks really good.

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mrfirepro

Been giving this some thought and have decided on the following actions.

 

I'm not happy with it outside the tolerance ranges so decided to

 

Move the piston to another location on the crank and see if the out of tolerance moves with the piston which if it does will show it's the conrod and if it doesn't will show it's the crank.

 

Does this seem sensible or am I missing something.

 

If it ens up being the conrod, I can get a new piston/Conrod, if it ends up being the cranks I can either change it or get a regrind.

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Tom Fenton

OK moving the rod may prove that is the problem but you'd be better off to measure the crank journals as well to see what is what. You will need a micrometer to do that, forget vernier calipers they don't have the resolution required.

If it is the rod you can have it resized at a decent machine shop, personally I prefer this approach as it means you keep the rods as a matched set rather than introducing an oddball.

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mrfirepro

Tom - good advice, will get hold of a micometer.

 

Going into the garage to take it all apart AGAIN :angry:

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mrfirepro

Moved pistons around, and the problem stayed in the same place. So (I think) this proves it's the crank

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Tom Fenton

Did you have the crank checked by a machine shop?

 

Also it would be better if you kept your progress all in one thread as you have started bloody loads but there is no progression through any of them.

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mrfirepro

Yes & No, the chap I bought the block from said he had it balanced & checked and it was all OK, perhaps I should be so trusting.

 

I agree I have posted lots of threads but they all relate to problems I am having with my build, looking at the structure of the site, engines, bodywork, ice , suspension etc etc, it felt to me that questions on these particular topics should be asked in the correct section, if this is wrong I am more than willing to be educated and pointed in the right direction.

 

I have also reviewed a few of my threads and it does seem to me that they have all come to a natural conclusion one way or another, however if there were any threads that were of particular concern, point them out and I will finish them accordingly.

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Tom Fenton

You misunderstand what I am saying, if you keep it all in one place it makes the progress easy for everyone to follow, that is all.

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mrfirepro

Borrowed a micrometer, checked all journals, which all seemed correct.

 

Just for a sanity check I did the following.

 

on each journal I set the micrometer between 3 and 9 o'clock and checked this reading every 45 degrees. all journals were almost identical.

 

Can anyone offer any further suggestions, as I must be doing something fundamentally wrong.

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allanallen

'Almost' identical?? You're looking for 1-2 thousandth of an inch difference between journals.

 

You need to be very careful to get exactly the same feel with the mic, the difference between a heavy and a light feel can be 2 thou/0.05mm.

 

Swapping the rod does sort of confirm that it's a problem with the crank, I take it you used a different bearing when you swapped the rod too?

If in doubt I'd get it to a machine shop and have it checked over for size and straightness.

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Tom Fenton

As Al says using a mic is very much down to the skill of the operator. Within reason you can make the mic tell you any size you want plus or minus half a mm.

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mrfirepro

Thought I would give it another try this evening with the new block, same result.

 

Allan - the shells are all new, kept the same shells with the rods.

 

Thanks for advice, going to machine shop tomorrow, will let you know how I get on.

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mrfirepro

Just to close this out, Crank and pistons went to the machine shop a few days ago and one of the piston big ends was knackered.

 

he fitted a new con rod and now I have the block rebuilt and all clearances are within spec.

 

Thanks everyone for your help and support.

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