16 replies to this topic

[m1n1]

Reground crank and bearings bought from med in 2005.
20 000 miles covered since then
no noises from the engine, just a stripped for a gearbox rebuild and check-over.



can anyone shed light into why one of the shells from each rod is worn down to the copper on one side? the shell was the bottom one. Crank seems unworn and smooth, the shell is smooth also i.e. no scoring.
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[MRA]

incorrectly sized thrusts is normally the cause of this one

I would also say that the worn one is normally the top shell, and that opposite opposed is also worn to a lesser state, this is caused by the crank moving along the block and the conrods having to "tip" over to carry on working, canting over on the big end journal

[m1n1]

thrusts. ok will get measuring with the dti.

[alexcrosse]

yep, i agree with martin, thrusts you running helical drop gears?

how did your movie plans pan out?

Edited by alexcrosse, 20 July 2010 - 10:24 PM.

[m1n1]

Yes helical std A+ drops. The idler was rattling as the thrust washers were incorrect, new roller bearings and thincker washer has cured that. I also have a new primary gear coming in the post, and a set of rings.
will measure up tomorrow and order new shells and prob next size up c shape crank thrusts as i was supplied std ones 5 years ago.

[Dan]

One size up? There are only 2 sizes, to make an in between set use one size on one side and the other on the other. Measure it well and make sure you get them in the right way around.

[R1minimagic]

Would also be worth checking the pistons, rings, and bores for wear as that area could be affected too.

[MRA]

I would also check the crank thrust faces.........

If in good condition then I would check how much end float and set it from there.

[Sprocket]

Has anyone realised how much slop there is in an A series bottom end? how would a slightly larger thrust clearnce cause this type of wear on the big ends? Dont forget that two of the big ends are oposites, so the wear patch on at least two of the bearings would be on the oposite sides to the way they are shown in the picture. If it was thrusts that caused this, you might expect to see the wear patch in the same orientation on all big ends

Plastigauge all the bearing clearances.

[Sprocket]

One size up? There are only 2 sizes, to make an in between set use one size on one side and the other on the other. Measure it well and make sure you get them in the right way around.

Dan there are infact four sizes available, those being STD, +0.003", +0.005" and lastly +0.030". The 0.030" thrusts are used in such a way that you measure your thrust clearance using a standard set of thrusts, then have the +0.030" thrusts surface ground to the correct thickness.

You are correct however in the way you can achieve more than just the four stated sizes by mixing and matching different sets, per side. If going to the trouble to have a set of the 0.030 thrusts ground, consider using a standard set on the thrust side, and the ground 0.030 on the non thrust side, that way if you rebuild the engine, you can slip in new pair of standard thrusts without having to go to all the trouble of getting another set of 0.030 thrusts ground down.

[m1n1]

im not an expert. i seem to learn from my mistakes but after 10 years am getting there! not yet cleaned up the block and put my dti on the crank but if i push/pull on it i can feel a tiny bit of movement. (But not enough to slow down the engine when clutch was depressed) which happened to me once ages ago.

[m1n1]

okay, i have 5 thou movement when i pull it back and forwards.

this is to much yes?

[R1minimagic]

Did you check the pistons?

[Sprocket]

okay, i have 5 thou movement when i pull it back and forwards.

this is to much yes?

0.005" is fine, its at the upper limit, but fine. If you are that concerned about it, I would buy some +0.003" thrusts and use just half of that set on the non thrust side, then recheck that the clearance is 0.0035"

As I said, I doubt the thrusts have anything to do with the wear on the big end bearings.

What do the Main bearing shells look like?

Plastigauge all bearing clearancies

[m1n1]

hmm. my pistons are in good condition - a few marks in front and behind but not side to side but im happy with them.

the mains are the same, in that the bottom half is wearing worn to the copper.

i will have to mail order a plastigauge, cant think where to get it round here.
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do you think that the crankshaft has not been ground to size correctly?