9 replies to this topic

[HarrysMini]

I saw this asked on here recently, but I can't find the thread anywhere. And I don't think the question was answered anyway. 

 

I have bought some main and big end bearings for my engine rebuild. I went ahead and bought the 10 thou oversize ones however, in hindsight, I probably should have waited until my crank was back from the machine shop.

 

On the box, on the Minispares sticker, they both say 10 thou oversize. However for the mains, the manufacturer's sticker says 3M2205-.25, also, they each have 0.25 stamped in them (the big ends have 0.10 stamped). Does this mean that Minispares have supplied me with 25 thou oversize mains? If so, they are also labelled wrong by them, as they say 10 thou.

 

The bearings are ACL. 

[ACDodd]

No. 0.25 refers to the metric size. 0.010" is the imperial equivalent.

Ac

[minimadles]

1mm is 40 thou as near as so like ac says .25mm is 10 thou so as long as your crank has been ground 10 thou you will be ok you can't get a .25 thou shell anyways so it must be the metric equivalent

[HarrysMini]

Okay thanks for that, I was hoping it would be a simple answer. I'll make sure the machine shop take 10 thou off of what ever it was originally.

[minimadles]

Have the crank measured first just to be sure it hasn't been ground already or check the old shells I go the other way measure,grind , check remeasure polish then get bearings to suit just in case

[HarrysMini]

I'm fairly sure, judging by the state of the shells, it hasn't been ground before. 

 

The machine shop is measuring everything at the moment to determine what actually needs doing. I've asked them to do a 10 thou regrind on the crank journals as they were quite scored and on one journal there had been some kind of bearing failure. 

[Vipernoir]

A 10 thou grind isn't a great deal off the surface of the crank (it's only 5 thou off all the way round) so you may find that after a bearing failure you need to go to 20 thou to clean it up.

 

After we spun a bearing and trashed a rod, the crank needed 30 thou taken off to clean it up.

[Cooperman]

Yes, I've had that a number of times and needed to go straight from standard to 0.020" undersize.

[minimadles]

My sentiments exactly pointless going 10 thou if it doesn't clean the crank journals up at that .like you say if it spun a shell or had a bearing fail 10 thou doesn't always do it that said your machine shop will advise you what's required once work has commenced

[HarrysMini]

Well it wasn't a particularly catastrophic failure, I think it had just over heated. See pictures below. 

 

 

I don't have any pictures of the actual journal, but you can feel a kind of 'step', almost as if a section has come away. The machine shop said that a 10 thou grind will probably be OK but they will measure it.