bent valve and rebuild

[pac00t]

Hey dudes,

I let the darn chain slip and bent a valve. I took the head off and can see daylight looking into the exhaust port. While it's off I'm going to clean it out and such. When I did a compression check before messing up the valve it was all good. But I'm still wondering if I should take the cylinders off and clean them. The tops of the pistons have quite a bit of carbon.

Should I just measure the cylinder walls with the pistons at bottom dead center? Or is it worth it to take the cylinders off.

And where could I get a single valve and a head gasket?

Thanks

[pac00t]

oh, and what method do you guys suggest getting carbon off of the aluminum?

[xssiveone]

If the compression was good, why mess with it? You can't find original rings for these bikes. The only source seems to be the aftermarket large bore kit. If you take the cyl off, you risk breaking a ring or scoring the cylinder wall. If it ain't broke....

As for the carbon on the pistons, a soft bristled brush in your drill should work fine. Or a gentle scraping. Move each piston to TDC and then remove the carbon. Be careful not to disturbe the gasket at the base of the cylinders.

As for a head gasket, I don't think you will find one outside of purchasing a complete kit, usually around $60 or so on Ebay. I haven't looked for a while so the price may have gone up. As for the valve, no idea but I'm sure somone else does.

One note on the head gasket. The original head gasket had a rubber insert around the cam chain cavity. The new replacement does not use the insert. DO NOT try to put it in or you risk serious damage to the head.

[trbig]

Pac,

I've had the head off of mine a couple times now, and I just re-use it. If I was doing a rebuild, I'd replace it, but it only costs a little more for the WHOLE gasket kit than just the head gasket. Actually... my local shop wanted $100 for JUST the head gasket, but it's cheaper here online. On Partsnmore.com, it's $77 for a complete set. But.. like I said.. if you took it off carefully, I would re-use it.
As for the base gasket... take it easy, just in case, but in most cases, it takes dang near a stick of dynomite to get that thing off after your head removal. I was reading in my book when I was just doing this recently and it says, "It may be necessary to tap the cylinder lightly to loosen it from the base gasket" I was like... lightly with what??? A wrecking ball?? lol.

Are you simply replacing the one valve?


Tod

[skids]

The carbon ring on the cylinder walls near the top of the piston's travel should not be disturbed, according to the info I have read. Also, you risk getting a wire bristle or other crap where it shouldn't belong. While the head is off, tip it and pour some solvent (ie kerosine) onto the valve to check for the rate of leakage. That can help you spot other valves trouble. If I take a head off, I lap the valves to help recondition the valve seat.valve contact. Cheap, but effective. Also, before to saturate everything with solvent, look for oil soaking around valve seals to see if that job is also needed. Shoot, you may as well do the cam chain while you are in there if it is time...

[pac00t]

yeah, I'm replacing the cam chain. And yes, I think I only need one valve.

But wow, yeah thanks for the info, I won't mess with taking the cylinders off. I'll have to look at the head gasket again, but it looked to me like some coating or thin layer was coming of in parts.

Anyone here got a valve they'd let go

[trbig]

They'll need to know what kind/ year of motor the head is from. '80's and later have bigger valves... also whether it's an intake or exhaust. You might try to PM Andreaswise. Whatever price he gives you includes shipping, and his prices are hard to beat if he has what you want. If you do get a used one, the book says to make sure and use an oil stone and remove any burrs or deformations on the stem end to keep from messing up your valve guide.

Tod

[trbig]

Also.. here's a link with some info if buying new. Like I said, I don't know what year motor you have, so these part numbers may not apply, but at least it's a few sites that actually have them.

Link

Here's a link to the Yamaha parts website. Just put in your info, and it will show you a parts fiche so you can see what the numbers are that you need. Just click the "Proceed to parts catalog" button.. you don't have to sign up.

Yamaha


Tod

[pac00t]

Thanks.. the head is off of a 79sf. And it's an exhaust valve

[TopCatGr58]

Hey Pac,

New valves from YAMAHA run around $35.00 EACH ! I had to replace a couple myself, but only a couple. BUT while I had the head off, since I was doing a topend rebuild, I pulled all valves, and seals, and lapped them all, put in all new seals.

Tod must have forgotten, but when he was doing his engine work, I had found a site that had the head gasket for around $35.00!!! I think I used the YAMAHA official part # and googled it, and found it that way!

Wish I had had this site to refer to 5 years ago, but I didn't and so I didn't replace my cam chain.
T.C.

PS, search Ebay for this item: 300018067288
From ATVUnlimited, Composite Head Gasket....like from Cometic brand (same as Graphite one for my big bore) but for STOCK size cylinders!! $39.99 + $6.50 S&H!!!