ATC90 Engine Rebuild Question

[Frankencelery]

Last year I bought a '72 ATC90 for my son to ride. It had very low compression so I had the cylinder bored and the head redone. It also needed a chain and sprockets, so when I got the top end parts back I took the left side cover off and found that the case is broken around the sprocket area. So I purchased another engine. This one is a '78, and I just assumed that my cylinder jug and head would fit. I haven't started on it yet, but I thought I'd better ask...will it? I just assumed they were the same, but any advice from those more exprienced would be appreciated.

[MTS]

Last year I bought a '72 ATC90 for my son to ride. It had very low compression so I had the cylinder bored and the head redone. It also needed a chain and sprockets, so when I got the top end parts back I took the left side cover off and found that the case is broken around the sprocket area. So I purchased another engine. This one is a '78, and I just assumed that my cylinder jug and head would fit. I haven't started on it yet, but I thought I'd better ask...will it? I just assumed they were the same, but any advice from those more exprienced would be appreciated.
im 99% sure they should fit....they also swap out with most CT90 internals too.

[Frankencelery]

Yeah, I'm right in that 99% range too. I guess I'll just have to try it and find out! While I'm at it, should I replace the cam chain when doing a top-end rebuild? What about the sprockets? I had everything else, but I didn't bother with that.

[Vealmonkey]

All those items are good to replace. Pay close attention to the chain adjuster roller assembly that takes the slack out of the chain and make sure the rear bearings are good, bad bearings will prematurely wear out your engine really fast. Don't forget to look at your clutches, you have to get all that new found power to the ground.