Some of the engine builds I have read say to not use the locking tabs but a washer of the same thickness. If this is correct what grade do they have to be - something like a grade 8 high tensile?

Cheers - the engine building noob

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Dave K.
1979 Moke Californian + 1981 'Coke' Moke

Use NO lock tabs on the mains. Or washers either. The steel the tabs are made from these days is too soft.
But do screw each bolt into the block without the cap, measure up to the head and make sure this dimension is less than the cap thickness.
Clean the threads out with a 7/16" UNF tap if you have one.
If necessary, shorten the bolts by 1mm or so.
Don't Loctite the bolts- just oil the threads and under the heads.

re the big ends, I (and GR) don't use lock tabs there either. If they are ARP bolts I use their moly lube supplied, otherwise engine oil.

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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 wouldn't think this be a "safe" idea. It may be practical on race motors where they are being pulled down on a very regular basis so not dealing with the tabs would save some time. Their designed to prevent bolts and nuts from coming loose.

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Respect mine and I'll respect yours.

I bin the lock tabs, no washers and use a bit of left over ARP thread lube from my rod bolts

one of the properties of loctite is that it is actually a thread lubricant until it sets, so theoretically it'd be the thing to use for main cap bolts - lubricate as they're screwed in, then hold them in once set. But I've never had an issue.

Yes they were, but back then they were made from real aussie or UK steel, not made in PRC from magnetic cheese.
If you give it a good rev (miss a gear) the tabs collapse, you then have lost bolt tension on the assembly.
Most 1275s had no main bearing locktabs anyway. Or rod bolt ones.

ARP fasteners recommend use their moly lube and torque to give a bolt stretch dimension (on their rod bolts). It is the elastic stretch of the bolt when torqued up that keeps it tight, not a cheesy lock tab.
They recommend use this moly on their main bolts too.

[edit] The problem with using Loctite is the heat from torquing them up can hasten it setting, so the actual torque is not correct. I used to use it but not any more.

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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.

More importantly, make sure the spot facings are 100% perfect.

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....and there is a chamfer in the hole to clear the radius under the bolt head.

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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.

Is that the same when using ARP Main Studs? Bin the washers they came with or use them?

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1962 850

If they came with hardened ARP washers I'd use them, I was talking about the stock 998/1098 & 1275 bolts in my post above.

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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.

The ARP washers are proper high tensile steel like the bolts/studs themselves so you want to use them unless there is a height/clearance issue with the g'box that precludes this. (Which can be an issue).

cheers

Kevin

edit - The good doctor beat me to it!