Engine Rebuild - any advice?

Thanks. That's next. Moving slow, though. Lots of work, and Chicago winters are making it unpleasant to spend too much time in the garage.

 

THAT'S an easy one: http://www.northerntool.com/webapp/wcs/ ... _200307957
Toasty! I wall-mounted mine and parked a propane bottle outside the garage, ran a line inside.

 

You mentioned the propane heater before. Someday I'll have some extra moola to afford one but right now I'm making due w a couple of electric heaters that I was given (I dont pay for the electricity in my garage).

 

Alright. It's warm out and I finally got the head over to Champion Cycle at Western and Addison. Paul took a look at the ring of rust around the cylinder and told me that it was shot. I'm pretty sure it would cost me more to get oversized pistons than to buy a new engine. Paul also tried to sell me an '83 Maxim.

So, a few questions:
1. What do I do with the old engine? Part it out? Sell the aluminum parts?
2. Do any of you know of a 650 or 750 engine near Illinois that I could get for cheap... REAL cheap?

 

Buy a replacement set of cylinder jugs...........might be the cheapest solution!

 

Help me out with a quick vocab lesson.

The part that is rusted on my bike is one of the four cylinders that the pistons travel in. The upper part of the head.

"cylinder jugs" - are you suggesting I purchase a new set of pistons, or do you know of a place where I can get a head?

 

From your description of the problem, it's not the cylinder head that needs replacing, it's the "jugs"....the actual cylinders that the pistons slide up-and-down within. The cylinders ("JUGS") and the cylinder HEAD are two separate parts.

And those JUGS are actually made up of two components, the cast aluminum, finned cylinder "shell", and four cast iron, replacable cylinder LINERS. It is actually those liners that wear, since it is the liners that the pistons and their rings actually ride up-and-down upon. Howeverm the cost and effort involved with replacing individual liners is usually not worth the effort.

The cylinder HEAD is where the valves and the camshafts live.

Depending on their condition, you may or may not need a new or used set of pistons (but probably will need/should replace the piston RINGS).


Of course, any used set of cylinders may need to be honed, or even bored out to an oversize to get the walls smooth. Minor rust on the ylinder walls can normally be cleaned up with a minor hone, which will not require new pistons. You can't really tell until you have them in your hands (or buy from a trusted seller) and measure the cylinder bores and their taper (besides the visual inspection for rust, scratches, etc.).

For your info, the cylinders for a 750 engine are:

65.00mm diameter, with a service limit of 65.10mm (before requiring an oversize bore).
Taper limit: 0.05mm
Ovality limit: 0.01mm
Piston-bore clearance: 0.030 - 0.050mm, with a service limit of 0.1mm


Further information on how to measure and determine wear parameters will require that you, or the machinist, have a factory Yamaha service manual or Haynes workshop manual for that engine.

However, if you take the above specs to your shop, and they get kind of a blank look in their eyes or try to blow off your desire to see that the measurements are done, then I would thank them for their time and take the work elsewhere.

 

For example...
This is not good
http://cgi.ebay.com/ebaymotors/1982-Yam ... ccessories

This is much prettier WITH pistons and rings.
http://cgi.ebay.com/ebaymotors/1982-Yam ... ccessories

Or get really spiffy. (they sure are pretty) but no pistons or rings
http://cgi.ebay.com/ebaymotors/1982-Yam ... ccessories

OH...wait, did you say it was a maxim or seca?

And then you'll need to buy a head gasket from Chacal!! ...hmm that reminds me.

 

Thanks, guys. It is the HEAD, not the JUGS. Sorry about the confusion.

Thanks for the ebay links, too, although I'll need it for a 650, not a 750. I probably led to that confusion. I was thinking that if I'm going to have to buy a whole new motor for the bike, it might as well be a 750 which fits into the same frame.

That said, it looks like I will not have to buy a whole new motor. Just the head. Anyone around Chicago have a 650 head?

 

Okay, but now that leads to another question, why would rust on the cylinder head disqualify it from further use (at worst, it would need a valve job and valve guides).............

But, if you do go head shopping, make sure it's off a 1980-81 650 engine, "non-YICS". The later 650 engines use a YICS head which won't be the same for your engine.

By the way, the 750 engines are not quite direct drop-in swaps for the 650's, so if you do decide to go that way, give us a shout so you can be prepared for what you'll run up against.

 

What he said >>

And if you have the head off, you probably should check the pistons and rings. You'd be bumming if you spend money on a head and have bad rings and she still wont run.

 

I think we still have a terminology disconnect here; the HEAD is made of alloy and cannot rust.

 

My bad, guys. THIS is the part that is rusted:



Not the PISTON inside (despite the appearance in this picture, all of that rust came off the top of it). The housing:



Bear with me. I'll get it.

 

So, the question is: Where can I get this cylinder block cheap?

 

Ebay is your friend!

There are a lot of them out there.
Shop carefully and make sure you get lots of good pics of the inside.
It would be nice to get a set of pistons and rings with it.

You should be able to get something for less than $75 but DON'T be a penny pincher if there is one that looks good for a couple bucks more.
You'll have a lot of time invested along with $ for gaskets to skimp on parts now.
Regardless you'll want to run a hone down the holes to clean them and true them as much as possible. You can get a cylinder hone at most autoparts stores