Centre main strap/cap/bolt thread engagement
Turbo Mini Forums

I've been looking closely at my block of late as im approaching the last stages of the build (rods/crank/flywheel/damper/sprocket balancing, painting components red/yellow for extra bhp etc).

When removing the crank after a dry build of the timing gear I suddenly realised that the bolts for the center main strap only engage around 10mm into the threads in the block

Is this going to be a problem? I've just measured another cap/bolt to be around 18mm bolt thread going into the block.

I've seen the future and tbh its Pie

If it was a Stud, you could probably 'just' get away with 1x the diameter thread engagement length.
As you're using a bolt, in Grey iron, I'm thinking you want to be 1.5x the diamter, for thread engagement. That said, 2x the diamter would be better....

Edited by turbodave16v on 24th Mar, 2006.

just looked at mine, ther's at least 20mm of thread into th block.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Not really Pete - It's more to do with the stud being fitted loose, and tensioned statically; that is by winding a nut onto the other end of it...

I'd love to give a real interesting and detailed explanation, but I don't think there is much more to it. If there is - I'm unaware, and have generally followed the traditional 'rules' without questioning further.

from what i understand it is as dave said, its to do with ensuring the stud only sees clamping load , not additional load through nipping up to the bottom of the hole/threads, as this is the general design method used in determining strength of the fasteners used in the joint

also not sure if many people know but as a rule most torque figures relate to torquing the nut end as opposed to the bolt end, you probably guess this is due to the bolt having a much higher friction level when tightening

hope that makes sense

cheers guys, im gonne try and get some 90-100mm bolts to get the engagement over 20mm.

Would this extra thread in the block effect torque ratings? Maybe i should measure the cap for roundness again.

I've seen the future and tbh its Pie

didnt you get new longer bolts with your center main strap, the one i got had longer bolts in it and i thought this was the norm?

no longer a series, but still 1.3 turbo.

yep they were longer, just not long enough.
Might try giving simon a ring as he did the fitting.

I've seen the future and tbh its Pie

Sorry to resurrect an old threat, but I was wandering if you managed to find so longer main bolts, if so where dis you get them?

I ask as I'm on the look out for a pair, since the chap who built my donor engine used grade 5 bolts which I'm not over impressed with.

Are you sure they are grade "5"? As they could be grade "S" which is something very different?

Most numbers on the end of bolts suggest a metric bolt e.g. 8.8 grade bolts. On an imperial bolt i have only ever found letters, but some people may have had other experiences.

i havent got round to getting any, but will stock up when i do. If your still struggling gimme a shout.

I've seen the future and tbh its Pie

Just had a quick search of the net and Minispares sell them. As an aside I noticed that MS centre straps are less than half the price of the Avonbar ones, which makes me wander if there's a difference in the metal used or are they both the same.