View Full Version : TR 3 Propellor Mounting Bolts Gr. 5 or Gr. 8

08-30-2008, 02:27 PM
Finishing the refurbishing of the propellor shaft this weekend and will be mounting it to the Differential. Should I use grade 8 bolts or Grade 5? Or does it really matter?

Your thoughts appreciated, Tinkerman

Don Elliott
08-30-2008, 04:55 PM
Eighteen years ago, during my full body-off restoration, I changed the drive sgaft bolts at each end for stainless steel bolts. I assume these were Grade 5. I used new stainless nylocs. They have been fine for 100,000 miles since 1990. I check them once a year for tightness and they have always been tight.

08-30-2008, 07:02 PM
I first used grade 8 but the length was a little long since all I could find were 1/4" longer than original length. It's a tight squeeze for the nylocs anyway and the extra 1/4" made it very hard to snug he nylocs. ISTR that the originals were a 1/4" increment in length - which is nearly impossible to find in your local hardware store.

Standard bolts follow a calculation for the amount of unthreaded shank versus threaded, based on overall length of the bolt. In shorter length bolts, this calculation often results and totally threaded bolts. I was told that this is NG and prop-shaft, flywheel, rear shock mounts, etc should have the proper unthreaded portion for strength. I ended up sourcing new bolts that have the proper unthreaded shank portion.

These particular bolts originally had an unthreaded portion equal to the two thicknesses of flange material, done for increased strength/decreased sheer at the threads.

08-31-2008, 02:43 AM
In other words, just buy the right bolts and be done with it. Yes, they are expensive, but lots cheaper than ruining the flanges.

08-31-2008, 05:35 AM
If they are similar to the later cars, the diameter of the unthreaded part is slightly larger than the threaded bit.

09-01-2008, 11:48 AM
I was able to source them out at Aircraft Spruce. They call the unthreaded length the "grip length". I bought 10 at .54 ea. They are grade eight, shipping was $4.80 for priority mail. Same place I got my ring gear bolts. I thank and credit someone on the forum for putting me onto that company. I am geting very forgetful in my advance age but I'm thinking that it was FJA or perhaps you Peter. Anyhow my thanks!!!!


09-01-2008, 06:54 PM
Good decision although it wasn't me that recommended Aircraft Spruce.