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**Ken Talbot** · 11-22-2005, 07:45 PM

Before you get too far along, you'll want to get a Clymers or Yamaha manual to read up on checking the pistons and cylinder bores. If the combination is out of spec, you'll be looking for oversize pistons and rings and will need to bore the cylinders. If you're going that way, you'll probably want to look into a Wiseco kit which will add considerably to the project cost.

A leakdown test before you go any further will tell you where your lost compression is going. If it's going back out the intake or exhaust valves, you may only need to do the top end which will subtract considerably from the project cost.

With just the head off, you may also find that most of your oil consumption is from tired valve stem seals.

Once you open it up, you're going to need at least a gasket kit and some crush washers for the headers. The gasket kit will give you a valve cover gasket, head gasket, valve stem seals, half moon rubber seals, crush washers, cylinder base gasket, and gaskets for the oil pan, alternator, and timing cover.

Some will probably say that if you're going in to do the top end, you might as well do the pistons and rings while you're at it. Of course, that only leaves the bottom end to complete the job. Let's wait for some of the real mechanics to log in for their advice on whether to go all the way.

**don07tncav** · 11-22-2005, 08:01 PM

Thanks Ken, I've got the Clymers and it's the reason I'm hesitant to tackle the job myself!! Plus there is no tech tips on this one like the Tranny fix for 2nd gear. Here's a list that I've got so far....

GASKET, CYLINDER 2H7-11351-01-00

O-RING 93210-77363-00

GASKET, CYLINDER 2H7-11181-02-00

PISTON RING SET(STD) 3J2-11610-00-00

GASKET, HEAD COVER 2H7-11193-00-00

Got a source for a gasket kit? Is this it??

3H5-W0001-00-XX TOP END GASKET KIT

**motoman** · 11-22-2005, 08:06 PM

I see there Don that Ken has given the same look-see tear down that I had said. Definitely valve guide seals, and am betting that just a top-end tear down will do fine, unless you see something unusual, would'nt go any farther, as I'm bettin the bike doesn't hav ethe miles to warrant it, unless money is no object, and wanna do bottem end just 'cause'.

**Ken Talbot** · 11-22-2005, 09:04 PM

Originally posted by don07tncav
Got a source for a gasket kit? Is this it??

There's a kit on Ebay now that is the same as the kit I have on hand for the project I started about this time last year. It doesn't actually have valve guides - it has valve stem seals. There's also a few individual gaskets.

**TopCatGr58** · 11-22-2005, 09:48 PM

Hey Don,

Sorry to see that you already spent $$ for some used cylinders and pistons, with just the description "Great Shape"? No mention as to the miles the engine had on it before it was torn down. The cylinders may have gotten worn fairly far out of round, and so a mere "honing" and going back with new OEM sized rings may not be enough to get it to seal properly!? I recently saw a set of oversize pistons on Ebay, but don't think it will be easy getting the standard oversize rings!? And, if you have to go to the oversize, you'd have to spend the $$ to bore the cylinders anyways, around $40.00 per hole! The head gasket runs $75.00 by itself, you get one as part of a Big Bore kit, since the piston holes need to be larger, can't use the OEM gasket with the big bore!

There are rubber seals around the Valve guides, but these are more rare and less likely to leak, vs. the valve stem seals which wear from the up/down action of the valve stem within the seal!

Pulling the head allows you access to replace the valve stem seals x8, and at least lap the valves and seats! You don't need the large bottom cylinder O-rings, just the head gasket.

AS for a timing light, not really needed with the 81, cause all you use it for is to "check" to see if the timing is correct, but there's NO ADJUSTMENT, the timing is controlled mostly by the TCI and the pickup coils.

My 81SH had an estimated 50K miles, I did the topend big bore, but didn't crack the cases, just put new pistons on the existing connecting rods, since most of my damage was top end rust in the cylinders, no problems with bottom end!! That was 5 years ago.

SO...hopefully you haven't pissed away your $$ on those used cylinders and pistons, you'll want to have them measures/mic'd for wear, out of round, piston clearance before ordering rings, cause if they are too worn, well, you've got a nice anchor!

Chalk it up to experience, and then order your big bore kit!
Good Luck!

**prometheus578** · 11-22-2005, 11:50 PM

Two problems to address first. Where's the compression going and where's the oil going. Could be two separate probs, or one contributing to the other. Need to do a leak-down test before tearing it apart. This will show if the compression is shooting past a bad valve(but wont pinpoint the oil prob), or if the compression is shooting down past the rings, which surely would also account for the oil loss.
If it's a bad valve, replace and lap in all the valves; new valve seals and you could be done. With the head off to do the valves you can check the cylinder walls for scratches, etc. With the pistons down, you can also measure most of the bore for wear. If it looks fairly good, you might consider leaving it alone.
If the valves are good and you're losing compression past the rings, then the cylinder must come off and check to see what the prob is.
Follow the manual when you have the head off and check the valve's "play" in the valve guide and measure the valve stems.
Really can't diagnose without seeing the parts involved but doing the leakdown test is a must, I feel. Just to get a better idea of what's going on.
In the last month, have had two bikes with almost identical symptoms. One was just a bad valve and the other had a broken piston ring. (Leakdown test sent me in the right direction)

**LoserShoes** · 11-23-2005, 08:22 AM

Quick and dirty diagnosis, have some one follow you and get on the gas hard and then let off. If it smokes while it's accelerating, its rings, when decelerating its valve stems.

Also check that the crankcase breather is not plugged, excess crankcase pressure can force oil past the rings.

Good Luck

Steve

**randy** · 11-23-2005, 08:39 AM

Sorry, Steve, you got that backwards.

The closing of the throttle on deceleration creates a vacuum spike that will suck oil past tired rings.

Smoke with WOT is oil getting past valve seals.

**don07tncav** · 11-23-2005, 03:30 PM

Aww awwwww, a delemma here. Do I take the side of the Guru or Truely Xsessive....

**motoman** · 11-23-2005, 03:33 PM

Guru....yeppersn that one Don

**flb_78** · 11-23-2005, 07:30 PM

you could just put 60 psi air pressure into the cylinder and try to listen where the air comes out. carb, bad intake valve, exhaust, bad exhaust valve, crankcase vent, bad rings...

**Ken Talbot** · 11-23-2005, 10:20 PM

Originally posted by flb_78
you could just put 60 psi air pressure into the cylinder and try to listen where the air comes out. carb, bad intake valve, exhaust, bad exhaust valve, crankcase vent, bad rings...

Do this at TDC for each cylinder in turn, and you've got a poor man's leakdown tester! Just a note for reference, if you put 60 psi into a cylinder that is a bit one way or the other from TDC, it will soon be at BDC.

**flb_78** · 11-23-2005, 10:23 PM

Yep, shoulda mentioned the TDC (top dead center part)...That coulda turned into alot false readings...

**GNEPIG** · 11-23-2005, 10:28 PM

.. the transmision shifted into 5th gear and the rear brake applied also helps keep the motor from turning over also

Announcement

What parts do I need now? Replacing the cylinders...

What parts do I need now? Replacing the cylinders...

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