Torque Setting Centre Main Bearing Cap

[Jamie]

I am just doing up the centre main end cap studs. Does 25lb/ft sound right? I have read this figure as being used on one engine on this forum, but I have seen 50 elsewhere.

Regards,

Jamie.

[David Grear]

I do them up to 60 LBS.
I do not install the shells.
I white metal the old shells then. I bolt the block to the crankcase and get the centre main line bored with the two bolts torqued to 60 LBS.
During final assembly it all feels too tight until the centre main is torqued up then all is well.
This way you know that front ,rear and centre bearings are all in line.

[Speedex750]

Hi Jamie,

I use 35ft.lbs I'm sure the studs are capable of more but I do wonder that more would start crushing the aluminium crankcase where the narrow shoulder bears. Anything more than 25ft.lbs should be OK, but be consistent and make sure everything always goes together the right way round.

Dave

[Jamie]

Thank you for the replies, which are really helpful.

Dave: a daft question, but how can you tell which is the correct way around for the top and bottom caps? Mine go in either way around and I can detect no discernible difference in the fit.

Regards,

Jamie

[Speedex750]

Hi Jamie,

You're right they will go in either way round. I've never seen any guidance on this but I think the tags on the shells should be resisting being rotated by the crank pulling them round by butting up against the other half. The two half housings do go together just one way so the tag recesses align. These half housings strangely aren't split across the centre diameter, one is deeper than the other such that the shell edges protrude, perhaps a crude way of centralising them?

Dave

[Jamie]

Thank you,, Dave, for the extra details. I shall follow your suggestions for the orientation of the halves.

Regards,

Jamie.

[Chris KC]

Jamie,

It probably makes little odds which way you install the housing unless you've done something to assure its alignment with the front and rear bearings. I recommend a read of grey mag 1985D (I can share the relevant pages if you don't have it) on this topic.

I have used 3/8" bolt fixings with 30lbft without trouble for several decades. Once the housing is properly sorted stamp alignment marks and torque figures on it indelibly.

I have never understood why people line bore the shells/ linings. Sort out the alignment of the housing and there will never be any further need to do so. But also appreciate that to line bore the housing you need to make at least a new upper half or there will be no metal to bore; and that it must be bored with the block bolted firmly in place.

Best of luck!

[Jamie]

Thank you for the reassurance about your experience using 30lb/ft, Chris. I would appreciate seeing the article, if possible. Although I have done a couple of test fits, I would be interested in reading the article. All seems well at 30lb/ft. It all spins freely. I used Plastigauge to ensure that there is a clearance all around the journal, which there is. I now need to see whether or not the crankshaft deflects when I tighten it up. Marking it permanently makes sense. Thank you for the suggestion.

Regards,

Jamie.

[Chris KC]

Sorry Jamie I missed your reply. pm me your e-mail address and I'll send you a scan of the article.

Yes, definitely check all is free when tightened up. If the block's not in place check again with that bolted on as it can heave things out of line.

An old-school bit of advice is to get the bearing bolts 'hand tight' and give the housing a gentle tap or two with a ball pein hammer to pop it into line.

[Jamie]

Thank, Chris.