Rod bolts

[tanny]

I have a 1973 240 and am rebuilding the engine. When I measured the rod bolt threads to determine whether I have 8 or 9 mm bolts, I came up with 8mm. From what I read the 1973 is supposed to have the 9mm bolts(I think). Any ideas as to what happened and should I torque these to the lower value as specified for the 8mm bolts. Are the threads where I am supposed to measure? Thanks, Vic.

[Phred]

Tanny,

I have built several L-24's and have seen both 8mm & 9mm bolts in that year. It seems they just used up their bolt stock, and then switched over to 9mm at some unknown (to me) eng. #. The bolt is measured at the thread. If you have 8mm bolts and are rebuilding, replace the bolts with ARP #202-6002 8mm bolts. They are actually stronger ( in tensile strength) than a stock 9mm bolt. The torque for the ARP bolts is 30 lbs. with Moly lube. When replacing rod bolts, The big ends should be checked for cap shift, (ID roundness and taper) and proper brg. clr. with the caps torqued to spec. About 90% of the time they require resizing. Wherein a few thousanths are ground off the mating surfaces of the rod and cap, the caps are then torqued to spec, and then honed back out to the proper size, which makes them perfectly round, with the correct brg. clr. All this can only be done by a quality eng. rebuilding shop. Prefeably a race eng. shop. This can be done with the pistons attached. If you are also replacing pistons, you could also balance rods and pistons at this time if your budget allows. Hope this helps.

Phred

www.arp-bolts.com

[tanny]

Thanks for responding. I was able to get in touch with the guy I bought it from and found out that he did replace the 73 engine with a 71(I don't recall him telling me that at time of purchase, but he may have). So I guess that explains the 8mm bolts. Will never race or really stress out the engine, so I'm not worried about the weaker bolts. At least I now know the torque setting(glad I checked the bolt size instead of just going with the higher torque settings for the 9mm bolts). Thanks again.

[Phred]

Tanny,

I should clairify, and note the official Nissan communist Party Line on replacing rod bolts. These were designed as a one time stretch

bolt. They recommend replacement at each rebuild.

General Info: Rod bolts 101

A rod bolt maintains its torque through tensile strength. This is measured as elongation in the bolt when torque is applied. Typical

bolt stretch is from .0055 to .0065 depending on the bolt type. When torque is removed, the bolt will "relax", and return to its original length. If too much torque is applied, the bolt will yield, or deform to a longer length than it was originally. when this happens, the clamping force is reduced or lost.

The Nissan bolt will not return to its original length after being stretched. Therefor the second time the bolt is stretched, it will not create the same clamping force as it did originally. A poor design for sure. but thats the fact jack.

Having said all that, I have used 9mm bolts over with no disaster taking place. But since the engines I've built have been for performance applications, I have never reused a stock 8mm bolt.

Note: do not exceed 28lbs. with a stock 8mm bolt.

Phred

[tanny]

Did not realize these were throwaway bolts. Who has these bolts you're talking about? Is there any source for the stock bolts? Thanks, Vic.