I need some new main and big end bolts for my 1100 rebuild... I've found what I need for the big ends ---



..but I'm not sure what I need for the mains?

Thread on mains bolts is 7/16" UNF.
Standard main bolts are fine if they are Grade 8. These have 6 slots cut in then, like a castellated nut.
Just check with a magnifying glass that the threads are not stretched or damaged.

If they are damaged I buy new ones, or buy Grade 8 bolts (6 marks on head) and cut to length.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks Doc. Yeah, a few of the main and big end bolts are buggered so I'm just going to replace the lot.

So I need ---
Big Ends: Unbrako 3/8" UNF Socket Head Cap Screws
Mains: 7/16" UNF Grade 8 Bolts

Take one of the mains bolts with you if buying bolts from a fastener place. They are an odd length, you have to buy longer ones and cut them off. And they MUST be Grade 8. Or get Unbrakos, (they are higher grade) if you can find them.
Easier to buy new mains bolts from Karcraft, if they have them.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I was just about to this silly question...

Karcraft have the main bolts listed as:
BOLT - MAIN BRG CAP - MINI 1275 (NOT S)

These are fine for a 1098 right? They're all the same apart from the 'S' that had 2" mains(?)

Cooper S all had 6 main studs & nuts, not bolts (except early 1071S in UK).
I'm pretty sure the 1275 bolts fit a smallbore OK, ask em or check length.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks for the help Doc, much appreciated

And those bolts in the early 1071S can not be replaced with the later S studs as the holes in the caps and block are a different (smaller) diameter.

Just a bit of trivia for a Tuesday night

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Steve

You should run a 7/16" UNF bottoming tap into the block, to ensure there is no crud and the threads are AOK.
Before bolting the caps on, run the bolts in by hand, check that the heads are 1mm or so below the cap height. ie not bottoming out. Shorten a little if needed.
Oil the threads and bolt head face when assembling.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.