I have an older OS 40SR engine and am looking for the bolts that attach the muffler. The housing of the engine is tapped to accept the bolts rather than having the bolt go through with a nut on the back. I no do not have the original bolts so I have no sample to take to the store. It is about a size 6 but a 6/32 is not correct. I wonder if it is a 6/40 but I cannot find that size. And metric sizes do not seem to fit.

Thanking in advance,

Laurence

There is always the choice to drill it out and use a bolt and a nylock or a nut with a lock washer.. and of course, with some locktite.

CGr.

Try using a 3mm bolt. The OS 46 use that size.

Unfortunately if you cannot source originals (my apoligies I do not know the size) through drilling and nutting is not an option. There is no exit and its a blind thread hole. If one were to drill on through, the exit hole would be on large curve with no land for a nut rest on.

These engines were produced in that ackward era between when OS first started including strapons and only a short time later when they got smart and cast in through holes in the cases and threaded the mufflers themselves

As a last resort drilling and rethreading the blind holes for SAE sizes may be an option.

John

I would have sworn it was a 3mm, but I just checked my .40 FSR and I can confirm that it is not. According to my bolt guage, it appears to be an SAE 6. As you have already found, it is not a 6-32. My guess would be either a 5-40 or 6-40. You can get either at [link=http://www.mcmaster.com/#socket-cap-screws/=81s4se]McMaster Carr[/link].

Just found a Slimline muffler for the FSR and it has 3.4mm bolts. Don't know where you can get that.

I just checked my 40SR, and it's 6-40 as you guessed.

Many thanks for your replies.
Now the problem is where to get just a few of the 6-40. McMaster Carr does have them but with a 100min. Guess it depends on how badly I need them.

Laurence

Have you tried an auto parts store? One with Dorman drawers might have what you're looking for.