Hey All,
I'm getting ready to put my 1800 into my 74 camper but have been held up by a problem. I have got 7mm 1.0mm thread Grade 8 high tensile bolts and when I try to tighten them up to 24ft/lb they will snap a few mm down from the head. What am I doing wrong?

The ones on the clutch beforehand were done up without washers so I have tried both with and without washers. I have tried lubricating the underside of the heads on the bolts with oil to reduce friction but no success. I am tightening the bolts bit by bit from side to opposite side but still manage to break at least one if not more. I have tried this with 2 different clutches also. The bolts will screw all the way into the flywheel without the clutch but break once they get some pressure on them. I have removed the burrs on the clutch bolt holes as well.

Any help is appreciated. I've never come across this before.

Steven

Only thing I can think of is check the torque is correct? (can you cross check with other books, or check your torque wrench?).
The only book I have handy covers the 1700 motor and calls for 18ft/lb.

Secondly high tensile bolts generally come in grade from 8 to 12, so perhaps try a stronger bolt. Just don't strip the flywheel.

Hi

I cant find any data on the 7mm bolts, but the 8mm ones that were used on 1700 & 2 litres only needed 2.5 mkg or 18 ft. lb.

Steve

they should be 8mm x 1.5 thread same as on a stock Beetle 1600
use the washer as it spread the load and acts as a locking mechanism as well

the heads of the bolts should have the number 8 or similar stamped on them

For M7 x 1 fasteners:

8.8 grade should not exceed 11 ft.lbs with a drop of oil on the thread.

I would estimate:

10.9 grade 14 ft.lbs

12.9 grade 18 ft.lbs

If you use ANY lube you must REDUCE the torque or the bolt will stretch or break.

Any excess lube should be removed, I like brake Kleen.

Even on 10.9 grade 8mm bolts I would be scared to use 24 ft.lbs.
...perhaps with 12.9 grade, but never with 7mm diameter.

Are they too long perhaps?

Interesting, thanks for the replies. The bolts aren't too long as they will screw all the way into the flywheel without the clutch attached. Can someone please have a look in their manual to check torque settings definitely for me. I may have misread it. I considered grade 12 bolts but qustioned whether or not this was necessary due to the old bolts being grade 8 also.

Cheers

Steven

Hi

I have Bentley Kombi manual, it doesn't list the 7mm bolts, only the 8mm ones. I always used 18ft. lb. on the ones on my old bug, which used a 215mm 1800 flywheel.

Steve

11 ft lbs is what I found for grade 8.8 as posted above.
this is for 7mm x 1mm pitch.

That came from a workshop manual.

Ok i now have got the Gregorys in front of me and can see where I went wrong. 18ft lb is 24Nm. Don't i feel like a dumbass..

Thanks for the help

Steven

yeah i can never remember the pitch on metric threads

A good chart to have hanging in the workshop! Below is the ISO coarse. The link to the ISO fine is at the bottom of the page.

DH

http://www.newmantools.com/tech/threadm.htm 

http://dodgeram.org/tech/specs/bolts/M_bolts.html 

good work charts

Ive got a thread gauge around here somewhere

i proberly have been overtightening them for years just do them up with a socket n bar never broken one yet I have broken a flywheel bolt must have been a weak spot LOL