Engine identification question's...

Alright so I have an 82 750 Maxim, it came with a Replacement Engine installed + the Original Engine.. Recently I've noticed some subtle difference's between the 2, and I'm starting to think my current engine is actually a later model YICS 700 from 85 or 86. There's a small Philips head screw/Bolt to the upper left of the Plug on the side of the Head that the 750 that originally came with the Bike doesn't have. I can't find this Bolt on any of the 750's so far, only the 700's. Are there any other notable difference's between the YICS 700 and the 750 that would be a give away for the Engine I'm currently Running?

 

The ID stamped in the casing will tell you definitively what engine you are looking at.

 

Engine ID starts on page 4:

http://www.xj4ever.com/catalog/frame-engine-id.pdf

 

The front of the cylinder block is also embossed with the displacement, right between 2/3 cylinders

 

Thanks for the info Guy's, It is a 750 Block.. This is the Bolt I'm talking about not sure why it's missing on the Original Motor's Head. As I said, the only Motor's I can find online that have it is the Later Model 700's. Just weird I guess.

 

I seem to recall that the question has come up before - and the answer is known only to Yamaha, but most likely long forgotten even there. Some have it some don’t. If you can discern a pattern then you win.

 

That screw/plug comes on all of the "later" 650/750 engines; earlier models did not have the screw, they had a lead (?) plug pressed into an unthreaded hole in the same position(s)....there are at least 4 per head. I believe it is a port to allow cleaning out of internal cavities after head casting/machining There are similar "lead plugs" on the other end of the head, and around each intake port (on YICS heads).

 

Ok, that makes sense. Appreciate the Help..