starting trouble...

[GLoweVA]

no change, and the piston has no holes, had the head off recently. on to parting it out...

NOOOO!!!, DOn't give up that easily. If the frame has a title, then sell the whole bugger together.

[natemoen]

yeah i am heading out to do a wet test now, valves are all shimmed up coreectly, they were a little out of spec initaially, but i can't imagine enough to bend them ill re-post in a few

I am not saying you did it wrong, but you explaining what you did and how you did it can help us to help you. Just sat they are shimmer up correctly doesn't me anything. I have "done things correctly" and ended up with bent valves, so that is why I ask for explanations.

So please, elaborat.

[Nick7777]

well i just bought the head off greg a week or so ago, got it, shimmed everything up, installed the head and torqued everything in sequence according to the manual. had the crank at TDC and the camshafts were placed in the head with the dots aligned to their respective place to the cam caps. i intaleed the chain and ACCT then rotated the crankshaft clockwise by hand 6 full revolutions to ensure my timing marks were all still in line. they were dead nuts. i put the carbs and coils on and proceeded to tunr the bike ignition and kill swithch to ON and RUN. after cranking for about ten seconds i stopped, and then procedded to check spark, fuel and then compression. and here i sit :\

[natemoen]

Did you shim the head off the bike?

Did you shim the head with it sitting on a table?

Did you have both cams in when you were doing the shims?

All of those have a high potential to bend valves.

[Nick7777]

yeah the head was on my bench. i did them one at a time so as to not run into issues.

[natemoen]

yeah the head was on my bench. i did them one at a time so as to not run into issues.

It doesn't take much more than a light hit against the bench to bend a valve.

I would say check you clearances again, I bet you will have a large gap on that dead cylinder.

[BA80]

The bench probably won't bend one but if you turned the cams one at a time with both cams installed it pretty likely that's how it got bent if that's the problem.

The valves will hit each other since Intake and exhaust are angled towards each other.

If that IS the case you should be able to rob the valve(s) you need from your old head.

Just clean them up and lap them in.

[Nick7777]

i am gonna pull the head off tomorrow. i can imagine it would be pretty noticeable. also have to rig up a valve spring compressor, as the one i have is for cars... if the PO didn't live three hours away he would be getting an ear full. last time i get a bike off of craigslist.

[TopCatGr58]

Hey there Nick,

Several of us have been there, I bent 2 valves doing the shims with the head off the bike because I didn't realize I couldn't have both cams in at the same time! The other bent valve wasn't noticeable, like George's, just slightly bent, but enough to cause no compression. Once I tore the head off again, pulled the suspect valves/springs, and spun the valve in the head/seat, I could THEN see the wobble!!!

There is a tech tip about being able to make a compressor from a simple large "C" clamp and some piece of PVC or steel tubing with slots cut in the side to allow access to the keepers!

T.C.

[BA80]

Sorry nick, I should have said something. You can adjust the valves pretty easily off the bike but just have one cam in at a time.

Also, When you install the cams after installing the head have all the timing marks, engine and cams, lined up as closely as possible.

You'll get it man.

[ViperRon]

One other thing to look for is a sticking Valves. When they sit it is possible to get some rust build up and if carbon has built up on the stem you can have a valve that sticks. If it sticks it is possible for the valve to either hit another valve in rotation or hit the piston. While you have the head off and are checking the valve for a bend or a wobble check to make sure it slides back and forth. Some slight resistance just shows the guide is tight but if it takes a hard push find out why. Check to see that the valves rotate also. The cam lifter valve design provides a little turn of the valve in every cycle to help valves wear even and not build up carbon. Another thing to make sure of is that the washers are under the springs in the head and that the springs are good. You should have good tension on all the springs. Once everything is back together before the cams are put in put the head flat on a bench and put some carb cleaner or paint thinner in the intake and exaust ports. If a valve is not seating correctly the fluid will leak threw. I am not saying any of these are problems with your buke but since you have the head appart they are simple things to look for and the more info you have the better off you will be.

[ViperRon]

One more sugestion is to not put the head on with the cams on it. You will need to route them thew the chain anyway and having valves down when putting on the head is always a risk of bumping them. Do like BA80 said and get everything in timming lined up correctly before you try to bolt the cams down.

[CaptonZap]

One other little detail, the springs should be installed with the spirals going in the right direction. Consult the service manual (Yamaha) for an illistration as to the correct direction. CZ

[BA80]

This head is off of a running bike Ron. It's only been laying in my garage wrapped in plasic for a short while.

No stcky valves.

[GLoweVA]

Something I just thought of,
If the head checks out okay, then the problem may be with the rings.
You say the piston tops all looked okay.
How about when the head is off, with that piston at bottom dead center, put a measured amount of 20-50 oil into that cylinder and its twin (also at BDC) and see which one the oil drains from first. This will be a "leak by test" past the rings.
Make sure you check your oil level in the sump and maybe drain some out if need be before you run it with too much oil in the sump.

If it is the rings, then pulling the jugs isn't that much more effort since you've got the head off already.