I have acquired an O.S. Max-III .15. It was missing the prop drive washer. It has a "D" shaped shaft where the washer fits. A friend of mine sent me prop drive washer of unknown origin that has very close to the right dimensions & I think would work except for two things- the drive washer "looks" to large in diameter at the rear, like maybe it was for an engine with a larger crank housing and, it has a counterbalance affair cast into the rear of it. About two thirds is hollow & the other third is solid aluminum. The counterbalance is the part that bothers me, if it's not supposed to be there I'm afraid it's going to vibrate like crazy. I just found a few pictures of one of these engines on ebay & it looks like maybe the large washer is the right part after all. I can't tell for sure from the pix. Do any of you know what this thing is supposed to look like? If I emailed you a close up picture of the engine & washer could you tell me if it's the right part?
TIA,
My recollection (I had two) is that the correct prop driver does look quite large for the .15, maybe because it was common for the .19. If the counterbalance is clocked to match the crank counter weight, I'd at least give it a try. Picture would be welcome, I can visualize the OEM part ok. Steve
Nils,
It sounds like the right part. I'm looking at an OS Max-III 15 I got new in the early 70's. The prop drive washer is as you described, and it matches the picture in the instructions.
Randy
It is the right part the 15 and 19 had same part , also the old 20 and 25 series - pre FSR that is
It's the correct part. It probably has "PAT PEND" and a "I" cast into the rear inside too. There should also be a small spring steel shim washer with the set, which keeps the drive washer pushed away from the crankcase a hair.
JK
It does have PAT PEND cast into the rear but I don't see an "I". I don't have the spring steel washer either, or a prop nut. Will it be OK without the washer? Any idea what thread the prop nut is? I'm having trouble finding anything to fit. My pitch gauge with my metric taps says it's a .8 pitch. I can find 5X.8 but they're too small. I can find a 6X1.0 but they're to course of thread. It's also bigger than a 10-32. I'm going to take it to a hardware store today & see if I can match something up. Thanks guys,
Nils
Nils: THe "I" will be over to the right, in another section, if it is there at all. The thin spring steel washer is really sort of overkill, the main purpose (according to GMA) was as a buffer so that if you used the engine as a pusher, the drive washer wouldn't gall the front of the case and bearing. It should be ok as is. Darned if I know on the prop nut size and all! Been fortunate enough not to lose mine so far!
Thanks Jake, I won't worry about the washer then. I'm off to the hardware store this afternoon in search of the elusive nut.....
Nutless Nils
Nils: I think you will find yourself highly pleased with this little motor. It has excellent power for a baffle .15 coupled with light weight and a durable and tractable nature. You will probably want another after you try this one, I know I did.
A pity they are no longer made.