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**cywelchjr** · 08-30-2011, 01:09 PM

Do NOT rotate the engine without the cam chain tensioner!

That is just asking for bent valves. Get the engine to TDC before you remove the tensioner and do NOT rotate the engine with the head still on and the cams still in place after that point.

**GLoweVA** · 08-30-2011, 01:21 PM

One of the manuals say to rotate 180 to get the other 2 cam sproket bolts out.
Can I get to these other 2 bolts with out rotating?

**cywelchjr** · 08-30-2011, 01:27 PM

I wouldn't pull the tensioner until after rotating the cams 180 (which is 360 on the crank, so it's the same position as far as removing the tensioner is concerned).

**GLoweVA** · 08-30-2011, 01:33 PM

Thanks Cy,
I'll start 180 out from TDC, take out 2 of the cam bolts, 'carefully' rotate 180 back to TDC, then take the tensioner out, then the last 2 cam bolts, then remove cam.

Does that sound like the safest way to go?

**cywelchjr** · 08-30-2011, 01:38 PM

Originally posted by GLoweVA View Post

Thanks Cy,
I'll start 180 out from TDC, take out 2 of the cam bolts, 'carefully' rotate 180 back to TDC, then take the tensioner out, then the last 2 cam bolts, then remove cam.

Does that sound like the safest way to go?

Either way would work, as normally if your doing the adjustment or removing you don't have the cover off, so you can't tell if your at TDC or 180 off, so as far as chain tension (which is the point here) it's the same thing. Once the cams are loose and not holding the valves down it doesn't matter anymore, cause turning the crankshaft is safe at that point.

**crazy steve** · 08-30-2011, 02:29 PM

Originally posted by GLoweVA View Post

So, if my piston is holed, can I get a 'used' piston and put it in there?
Or would it be better to get a set of pistons and the matching Jug and put those on? (Saw one of those on fleabay)
I kinda want to keep the engine with the bike. (Matching VINs)

Just replacing a piston, sometimes, sometimes not. If you do find a hole or any pieces missing off the piston, you really want to pull the motor and split the cases to make sure those bits didn't go somewhere they shouldn't have and make sure they're all out. Failing to do so can convert a repairable motor into scrap metal pretty fast....

**cywelchjr** · 08-30-2011, 05:09 PM

Originally posted by crazy steve View Post

Just replacing a piston, sometimes, sometimes not. If you do find a hole or any pieces missing off the piston, you really want to pull the motor and split the cases to make sure those bits didn't go somewhere they shouldn't have and make sure they're all out. Failing to do so can convert a repairable motor into scrap metal pretty fast....

+1 on what Steve said there. If there is a hole in the piston, the likelyhood of pieces down below is high enough that you would at that point want to pull the engine and go all the way through it. IMHO at that point, it MIGHT be easier to find a replacement engine. That said, I would keep the original and take your time and go through it to see if it's salvageable and if so rebuild it, it's always good to have a spare

, I do, plus I still have the original sitting there that I may well go through and see if I can rebuild as well. It did really have too much top end chatter, so I may be able to just rebuild the bottom end on it.

**GLoweVA** · 08-30-2011, 07:58 PM

I didn't think about the 'pieces/part' that might have come off the piston.
Thanks to all your help, I got the head off in under an hour.
Snapped a couple of pics:
http://s1197.photobucket.com/albums/aa422/gloweva/
The one with the hole is #4 and the other one is #1. They were at TDC after pulling the head off.

so, I'm thinking, with such a small hole, the material just got melted/burnt up.
I have had it running for some time since the hole had appeared. If there was anything down in the case wouldn't it have made itself known by now?
I could replace the jugs and pistons:
http://cgi.ebay.com/ebaymotors/Yamah...item53e7006b91
Or, I could just replace just the pistons:
http://cgi.ebay.com/ebaymotors/1978-...item48407ec831

**crazy steve** · 08-30-2011, 09:02 PM

Originally posted by GLoweVA View Post

...so, I'm thinking, with such a small hole, the material just got melted/burnt up.

Yep, that's a 'too lean' hole, so I doubt that anything nasty got in the crankcase.

If replacing just a piston, you'll need to replace all the rings with new; trying to run a used ring set in another bore, the ring set won't last long. It may be cheaper to replace the whole cylinder/piston set, but make sure the pistons are identified as to which hole they go in or you'll have the same problem.

Also be aware that there's two different piston types; the '78-79 match, and the '80-81 do too. You don't want to swap one for the other due to differences in piston domes and valve reliefs. I'd also lap the valves, as that one cylinder obviously got hot and may have damaged the valves.

You do need to find out what caused this; I suspect it was a intake leak, but could be a malfunctioning carb also.

**Barnfresh** · 08-31-2011, 05:36 AM

http://a2.sphotos.ak.fbcdn.net/hphot..._5040005_n.jpg

Your's looks a lot better than mine. I am also thinking about splitting the cases and doing a fix. I will need to replace the connecting rod. Just wondering - had your engine sat for a long time - perhaps stored outside? I think the cause is a sticky valve caused by a rusty valve stem when the valve sits open exposed to atmosphere... Just thinking...

**GLoweVA** · 08-31-2011, 08:31 AM

So you all were wondering what caused it?
One day while riding home from work in the rain, 2 cyclinders cut out.
I thought it was electircal (due to the rain).
Come to find out it was those blasted vac advance wires. ARGH
Well, after fixing that, it ran like crap and started leaking oil. (hole in piston and pressure build up in case)
So, after the fact (hind sight being 20/20 and all) I figured, by running home (30 miles) and near wide open throttle on 2 cylinders (just to maintain 55mph) #4 just got a little too hot.
Now for the really bad one that you all are going to yell at me for:
Since owning this bike (7yrs now), Not once have I vacuum sync'd the carbs.

I've had them off quite a few time to triple clean them and did the bread tie bench sync thing, but now knowing what I know about too lean conditions, I'm definitely getting a sync set up and maybe even a colortune.
Oh and I'm going to pay a little more attention to what my bike is telling me. (like not running it on 2 cylinders anymore)

I read somewhere on here that we can use the oversize rings and cut them down to fit the stock pistons. Is that correct? That way I don't have to get the overbore bigger pistons and bore out the jugs. (way too much work)

**natemoen** · 08-31-2011, 08:45 AM

Originally posted by GLoweVA View Post

I read somewhere on here that we can use the oversize rings and cut them down to fit the stock pistons. Is that correct? That way I don't have to get the overbore bigger pistons and bore out the jugs. (way too much work)

That is correct, you can used 1st oversized rings.

**GLoweVA** · 08-31-2011, 09:33 AM

How about the oil rings, can I cut those down too?

I'm leaning towards getting a set of jugs and the matching pistons that go with it.
No sense in fixing just one piston on a motor that has over 79K on it.
This way I'll have 4 newish pistons (w/ new rings) and it should be able to last a long while.
What about the piston pins? Should I get new ones, or reuse the old ones with new clips?

**natemoen** · 08-31-2011, 09:58 AM

You won't be able to use the 1st over wavy separator ring, gotta reuse the old one, but the 4 other rings can be filed down.

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