Cylinders are off . . .

[IanDMacDonald]

And, going to the machine shop to check out-of-roundness and taper. I'm praying that they're within spec. I really do not want to have them bored-over.

I was surprised how cruddy those cylinder studs were! The base gasket is a complete mess! The head gasket was a little messed-up by the front and rear bolt holes that are upside-down.

So, onto my questions . . . :

Should I be checking anything else? The head is good. Had the valve seals done three years ago.

I'm not experienced enough regarding measuring con-rod clearances, etc. Any tell-tale way to check to see if the pistons and cob-rods are in good shape without removing them?

The plastic sleeves that broke-off on every stud . . . Can those be replaced? I have a new base gasket. Looks like I should buy another gasket kit.

When I take the cylinders to the machine shop, I'll report back on what they found, and go from there.

The plan is to get all of this done now, put it away, and it's ready to go in the Spring. I have new tires and steering head bearings that have to be done as-well.

[Radioguylogs]

My Approach

The plastic sleeves that broke-off on every stud . . . Can those be replaced?

I think the purpose of the plastic sleeves was to mitigate rust.

I couldn't find any suitable material, so I wire-wheeled the rust off of them and slathered them in grease. Made me feel better anyway.

[DiverRay]

For the bottom end, just go with how many miles are on the engine. Less than 100K, I would not worry about it. I've been through three engines so far, and the only one I put bearings in was Special Ed's, and it had about 130K on it, and was getting a very hot top end setup with big bore pistons.
Use fogging oil or synthetic to cover EVERYTHING when you put the parts away. It's easier to clean dirty oil off as opposed to rust. Synthetic oil will always stick, regular motor oil will migrate and leave the steel to rust after a short while.

[IanDMacDonald]

Mike & Ray- Thank you for the advice. Yeah, those studs are nasty!

[IanDMacDonald]

Machine shop just called . . .

Asked when I was bringing the pistons in. Huh? I'm not taking the pistons off the crank! He asked how he was supposed to get the piston to cylinder clearance. I said "you're doing out-of-roundness & cylinder taper, nothing more". He was confused, as he thought he was honing the cylinders as-well (we talked about that on the phone as-far-as cost, nothing more).

Anywho, I gave him the 71.5mm dimension for standard ring size. He said he would check the cylinders using that dimension.

Should I be worried? This shop has good ratings. Am I the ignorant one, or are they pushing for more work besides simple measuring?

[DiverRay]

A good shop will try to be SURE of things. They would need the pistons, but you just want to know what is the spec on the cyl now.

[IanDMacDonald]

Right. So, if they say it's out-of-spec, it's a definite bore job?

[IanDMacDonald]

Also, can those eBay big bore pistons be used in an earlier engine? I know most had the later heads that used them.

[IanDMacDonald]

One more question, in the event I have to have the cylinders bored, should I go next size up (72mm)? Or, go bigger?

[3Phase]

Ian, it's going to depend on the size of the piston dome. I don't remember the dimensions on those eBay pistons but if they're flat top, they'll work fine with the older head if the shop can bore the holes straight. Obviously, they need the pistons. A mild dome will work too but the valves will be a little to a lot close; performance boost or a dead engine if you miss a shift.

[IanDMacDonald]

Machine shop called back. Cylinders are out of spec. I'm thinking I'll goto 72mm on the pistons?

Anybody else with opinions?

[MPittma100]

First Over Bore

Do the smaller over bore first. Leaves room in the cylinder for future repair.

[TopCatGr58]

Hey Ian,

Unless you've already been able to find the 1st oversize pistons and rings, GOOD LUCK. They are NO LONGER available from Yamaha anymore, that's why folks are doing the big bores because that's essentially their only choice.

Now, I did the smaller version that Wiseco offered, the 1179, but they were a ~$500.00 kit! The Japanese 1196 generic big bore kit is/was only $150 for pistons, rings, wrist pins, keepers, and gasket IIRC. You'll be spending a good $50.00 per hole boring. SO the generic kit is a considerable savings.

ViperRon installed it on his 80G.

Well, a quick check on eBay revealed something new!

http://www.ebay.com/itm/78-79-YAMAHA...2/142059811845

They are listed as from JAPAN, same seller is also offering the 1196 kit as well, but they've gone up to $170.00. But they are listed for only the 80-81 model??

http://www.ebay.com/itm/80-81-YAMAHA...-/142242677316

So...it looks like you do have a choice in going with the smaller standard type oversize kit.

BTW, I estimated that I had about 50k miles on my bottom end when I did my top end rebuild. That was some 25+ k miles ago, and it's still going strong.

Other's will say to get some Plastigauge and take the crank and con rods out to check. I say, if it's not broke, don't fix it! YMMV.

ALso found this, actual WISECO pistons/sets, it's one piston/ring/wrist pin/keeper/and spark plug, for $104 bucks with ~$9.00 shipping, so a kit of 4 would be ~$416 plus S&H, and they show that they will fit 78-81. It's the smaller 1179 cc version(74.0mm).

http://www.ebay.com/itm/74mm-Piston-...-/391190736809
T.C.

[red bandit]

It looks like we have some nice choices these days. If you are on a budget you can get a cylinder/piston set used. Of course you might end up with what you already have, needing a bore. But if you buy one with low mileage chances are it will be good. Good luck.

[IanDMacDonald]

Hi TC & everybody else-

Thank you for the recommendations. I actually found this overbore kit similar to what you found already, except, it's 72mm, instead of the 72.5m:

http://www.ebay.com/itm/78-79-YAMAHA....c100005.m1851

If you guys are curious, here is the website of the shop I'll be using, and their price list: http://www.automachshop.com/?q=node/...3%3Fq%3Dnode/3

So, it looks like this will cost me a few hundred dollars. I would certainly be interested in using those domed cylinders of the 1196cc Japanese kit, however, I know nothing about the internals of these engines, and whether those pistons can be used on the earlier engines.

I have a few other engines I could pull from, but I'd rather try to put new life into this engine, rather than go with the unknown and be right back to this point in another year or two. The Yamaha will definitely get rode more once I have new steering hear bearings on her. It's just too scary right now at higher speeds.

I guess I'll order the 72mm kit, and get that to the machine shop. I'll, of course, ask them if I need to go bigger than 72mm, or if it'll suffice. I'll keep you guys in the loof.

Thank you as always.