Just finished rebuilding my engine- little question.

[Math]

Hey, I'm done.

Couldn't start it though because I installed a new fuel tank and the petcock was leaking... a lot. I'll try a new OEM ring/gasket...

I have a question, as I was trying to push the kickstarter down with my hand, I noticed that there is more friction in the engine than last fall. I don't really know where it comes from. There is no weird sounds that would make me panic but the kick just does not go down easily even on decomp.

Here is a list of things I've done to the engine

Emptied the oil

Let it rest for the winter

Removed everything to the piston

Replaced rings (brand new, yes the orientation of the rings is OK)

Adjusted valves

Installed cylinder and cylinder head with new gaskets

YZ timed

Put the chain tensioner back to its place without playing with the adjustment

Replaced the spark plug

I think the problem might come from friction at the cams because when I was trying to put the engine at TDC to install them, the piston was mooving very smoothly in the cylinder even with the new rings. Another clue is that when the head was on my bench, cams installed and the caps torqued, it was quite difficult to make them rotate. Yet, I had previously lubricated them with molybdenum oil just like the service manual explains....

Any idea why there seems to be friction like that?

Hopefully, once the engine starts, oil is going to be shooted with pressure on the cams and things will get back to normal.

Thanks for your input

[new2blu]

If you just rebuilt the engine and had the cylinder honed---this would create more friction in the engine. It will go away after it is broken it.

[Wayward Son]

did you take the spring out of the tensioner and retract it before installing it?

if not,your cam chain is about 10 times to tight.

if the cams do not move freely in the head you either over torqued the cam caps or you have another problem there.

[Rip Wheeler]

...if the cams do not move freely in the head you either over torqued the cam caps...

And not to mention, maybe you have the caps swapped from one spot to another They MUST be in the exact spot they came from and in the same direction also, no exceptions.

[WheelsUp]

Ditto the tensioner... I'm not sure which bike you have, but the WR/YZ250F does NOT work the same way as a car's tensioner works, where it kinda floats in and out maintaining what's needed.

On the 250F, once the tensioner extends, it WILL NOT retract on it's own. It ratchets out to take up slop as the chain stretches over time, but it will not loosen.

You have to FULLY retract the tensioner, put it back into place, then release it. It'll put the proper amount of tension on the chain.

[Sylvain]

did you take the spring out of the tensioner and retract it before installing it? or caps swapped from one spot to another .

Math

The piston of the chain tensioner has to be retracted when you install it. Once it comes out it will not go in unless you use a thin flat screw driver to unwind the piston while you install the tensionner on the cylinder head.

What torque did you apply on the cam caps ? If you need it I got a 1/4 inch torque wrench for low torque setting.

I just got the missing part and the shims to get the proper clearance for my YZ cam. I hope to be able to finish the bike during the week. I'll let you know. We should get together to try out our reborn bikes

See you

[scott_h]

The tensioner is a good place to start as mention by all the folks above. Remove the tensioner; apply a little pressure with your finger and using a thin flat blade screw driver wind up the spring to retract the plunger. Apply a little more torque with screw driver to latch it in place (plunger will not move when you let go of it with your finger). When you install the tensioner, make sure you have right side up with the "up" marking oriented such that you can read it. Once it's bolted to the cylinder, use the screw driver to release the plunger and you should be set.

Don't worry about possibly swapping the cam caps since they are different on these Yamahas (six bolts on intake cam cap and four on the exhaust cap). Good luck and let us know how it runs.

[Frostbite]

Hey, I'm done.

Put the chain tensioner back to its place without playing with the adjustment

There seem to be 2 possibilities here.

1 - If the cams were difficult to turn while the head was off, then it wouldn’t have anything to do with the tensioner. I’m assuming that you realize that the cams would be hard to turn when the lobe hits the bucket, since you have to overcome the valve spring pressure. If you found that the cams were hard to turn when the lobes were pointed away from the buckets it may be wrong caps or over torquing like the boys said, or you may have warped one or both cams. I warped an intake cam a few years ago. I removed the caps when the intake valves were partially opened and the uneven pressure from the valve springs slightly bent the hollow cam.

2 – If you “Put the chain tensioner back to its place without playing with the adjustment” then you definitely could have a tight chain. When you remove the tensioner from the back of the cylinder it automatically moves to full adjustment, and it’s a one way trip, it can’t move backwards unless you wind it up manually. If you didn’t wind it up before you installed it then it’s at max tightness. Unless your chain is very stretched, I don’t see how you could have even installed the tensioner without winding it up. When it’s wound up you can push it right against the cylinder by hand and then install the bolts. Was this the case or did you have to pull it into the cylinder with the bolts?

Hopefully, once the engine starts, oil is going to be shooted with pressure on the cams and things will get back to normal.

Danger Bay - Do not rely on this. The cams should not be this tight.

[Math]

You guys have many good ideas and it would be too long to review everything so let's summarize.

1) I definitely have the tensioner problem. I'll have to readjust. I'll pull it back completely but then, how do I readjust from 0? Is it mentioned in the manual?

2) Regarding the cams, I'd be very surprised to have a bent (warped) cam. Good god Frosbite, what are your valve springs made of to be strong enough to bend a cam? Or did I get you wrong? Probably. The cap issue does not hold because the caps are different. But they might be torqued too much because I was at the limit with the wrench I used. I'll have to borrow Sylvain's torque wrench and check the valves again. Hopefully they will just get a little more loose (but still in the specs)which should not be a problem since they tend to tighten up with time.

Looks like I'm not done yet don't you think?

Many thanks for your precious help!

Oh! and for those of you who helped me last week, I succeeded to put the front chain slide to its place It's been really easy finally.

[Frostbite]

Math, you don’t have to adjust the tensioner, it’s automatic. You just wind up the spring, install it on the back of the cylinder and release the spring. Hard to believe but the stock springs are strong enough to warp the hollow cam.

[Math]

OK, I'll check this out. As for the warped cams, do you have a trick to check if they are slightly bent? I guess I could see it by putting them on a very flat surface. I'd bet my shirt they are not because I was at tdc when I removed the caps. But I probably have to check because there is so much pressure on the chain.. .I guess this could bend the cams too...

[WheelsUp]

AT THE LIMIT OF YOUR TORQUE WRENCH????!!!!???!!!

What wrench were you using? Those caps should only be getting 75 INCH pounds, not foot pounds! It's closer to 6 foot pounds. That is barely hand tight. You can exceed that easily with a 6" long 1/4" drive ratchet!

If the caps were overtorqued, especially by that amount, they are likely smashed out of round and require reboring. IIRC, Wrooster has posted links to a shop that can do the job properly.

[Math]

Wo Wo Wo Everybody stay calm

I'm talking about the lower limit.

The proper torque is 7.2 foot x pound and the range of the torque wrench I've used is 10 foot x pound up to the hundreds with a lower accuracy between 5 and 10.

Nothing is broken.. .not yet

Thanks for the suggestion of having it done by a shop but I've wanted to learn how to mess with these things all my life. I just want to do it myself to learn how. I probably look as somebody who doesn't know where he is going at all but in fact, I'd say it's not that bad with you guys helping and some other friends. I'm taking my time and I ask questions everytime something suspicious occurs.

Except making it for a living, I think it's the best way to learn. Just requires that I put my self pride aside for a while, patience, a full load of forgiveness for my own mistakes, service manual, good friends and TT of course .

Thanks again.

[Frostbite]

OK, I'll check this out. As for the warped cams, do you have a trick to check if they are slightly bent?

Take the cam chain off, re-install the cams and caps and turn the cam sprockets by hand. You should be able to spin them easily until the lobe contacts the bucket. Before I bent mine it would turn easily when setting up for cam timing. After I bent it it would turn but with difficulty and was obviously binding. hen I installed the new cam it spun freely. Since the intake is longer it may be more prone to warping. I'm not talking a big bend, just a thou or two, enough to knock it out of alignment with the bores.

[Math]

Thanks Frostbite , I'll have a look at that during the week. I hope that they're not bent and that setting the torque with a more precise wrench will be enough to cure the problem...

[Rip Wheeler]

... The cap issue does not hold because the caps are different...

Ah, not so fast. They are different from the drive end (sprocket) as it uses a bearing, what I meant was flipped over, even if its in the original end of the cam, it may be swapped from the same spot, but intake on exhaust and exhaust on intake. The same can be said for the other end where there is no bearing, just a babbit or oil clearance only.

[Math]

Ah, not so fast. They are different from the drive end (sprocket) as it uses a bearing, what I meant was flipped over, even if its in the original end of the cam, it may be swapped from the same spot, but intake on exhaust and exhaust on intake. The same can be said for the other end where there is no bearing, just a babbit or oil clearance only.

I'm sure that what you are trying to explain is important but I don't get it.

I know caps can't be installed on the wrong side because the drive end is different and made to match and cover the bearings.

I'm pretty sure you are trying to tell me that I could have installed the exhaust cam cap on the intake cam and vice versa. If this is what you are trying to tell me, it does not hold. The exhaust cam cap has four bolts and the intake one has six bolts. Have a look . It is impossible to swap them.

If I still haven't get what you mean, I'm very sorry... Please keep trying

[WheelsUp]

It is impossible to swap them.

There's a couple of shaved monkeys at my local Ford dealer that could do it.

[Rip Wheeler]

I'm sure that what you are trying to explain is important but I don't get it.

OK, my bad, I dont know why I was thinking it was seperate caps? I see now, this is impossible to get wrong. I had my 426 apart, its been quite some time, and didnt recall this set up. I must have been thinking of another model . Must be old age! We covered the torque already.

[WheelsUp]

It's the Toyota thang.

I had the caps off of both of my buddy's cams when we checked the clearances so we could document the stock shim sizes.

3 weeks later we returned with new shims for the intake and a YZ cam for the exhaust... I was going over the procedure in my mind on the road out....

including laying each individual cap on newspaper arranged exactly as it came out of the engine.