Exhaust Valve Guide Seal Question

cliffa said:

He, who never made a mistake, never learned anything.

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I make mistakes all the time . Daily .

cliffa said:

He, who never made a mistake, never learned anything.

Click to expand...

If thats the case… I should be a freakin genius by now…

If you never try, you never discover. There are several things about Commandos engines and gear boxes which are only discovered by making changes e.g. If you achieve an increase in torque, the way to find out you have it is to raise the overall gearing. If you have poor throttle response you need to change a couple of other things. In all of these cases, it might always be two steps forward and one step backwards.
When Japanese twostrokes came along, they had 18 inch tyres and greater angles of lean. So I fitted 18 inch rims and tryes to my Triton it did not corner faster and whenever I got off the bike after racing, I was always exhausted. - An expensive mistake and I lived with it.

Here are a couple of pictures of my pistons and rings. I regret that at this time I am not really qualified to diagnose their condition / orientation. That said, on the left side, (the one that was smoking) the ring gaps were right on top of one other, (as pictured) which I assume is a bad thing! Any comments welcomed. A mechanic friend fitted the rings for me, on Tuesday I will go and have a chat with him to see what he thinks.

I'm going to go away now and and do some research. Seems like the "Uh-oh" thread continues to have a lot of pertinent information.....

Cheers,

James

Britstuff said:

Here are a couple of pictures of my pistons and rings. I regret that at this time I am not really qualified to diagnose their condition / orientation. That said, on the left side, (the one that was smoking) the ring gaps were right on top of one other, (as pictured) which I assume is a bad thing! Any comments welcomed. A mechanic friend fitted the rings for me, on Tuesday I will go and have a chat with him to see what he thinks.

I'm going to go away and do some research now. Seems like the "Uh-oh" thread continues to have a lot of pertinent information.....

Cheers,

James

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Ring gaps lined up not ideal but not causing your problem. In fact, he may have installed them offset and they moved. You need to take the top two rings off - keep them oriented the same and look for a dot or ohter mark near the gap on the top - if none, look on hte bottom which would indicate upside down. If there are no marks, then look at the bevel in the inside of the ring and see if it is up or down.

The picture of the right looks good for the oil ring best I can tell. Need a picture of the left showing the red and green marking.

The gaps lining up happens as the rings rotate, this is normal and they would not be lining up within a short time. If you look at the 2nd ring down on the second pic ie the right piston you can see some odd waviness in the silver to black line as the tapered ring is starting to wear in. This shows at some points the silver is none existent so ring cannot be sealing at those points. Your left pistons 2nd ring has a much more consistent wear pattern, the silver is where the taper has worn against the honing ie its normal bedding in behaviour.

Hi Marshg246:

Thank you for your comments. You got me looking closer at the red and green markings on the oil control rings. Referencing the "UH-Oh" thread they should look similar to the following:




Not:



I think the left piston oil control ring may be installed incorrectly as above? Please see pictures below. Note the green portion is not visible as it is presumably beneath the red. The overall circumference of the left oil control ring seems to be less than the right. I wonder if this is the core of my issue?

Dear Kommando:

Thank you for your observations. That makes a lot of sense. Whatever I do I will not be reusing these rings.

Cheers,

James

Thanks for posting this stuff about piston rings. I would have fitted new rings when I rebuilt my 850 motor. Relatively speaking my motor has barely been used, but I have never thought about the rings not sealing properly. The gapless rings sound interesting. My motor is quick enough so I have not looked for more go, but if there might be more there to be had for almost nothing, I will seek it. Even if the gapless rings do not improve performance, they would probably not be a backwards step.

There is a lot of info on line re gapless rings - some pro, some con. Well, not so much "con," more as "they don't make any difference so why spend the money." Most competition engine builders I stay in touch with from my building days prefer standard-type rings that are produced slightly longer than normal to ensure their is sufficient ring to be able to be filed to whatever gap the builder prefers - which is based on how the engine will be used and whether it is naturally aspirated or forced induction. On a 4" bore, for example, the top ring gap might be anything from .014" (very tight!) to .027" Gapless rings do not have that sort of flexibility.

Note that the "longer" ring sets I refer to, above, are exactly that -the rings are longer but with the same diameter as a standard ring for the bore size. They are NOT oversize rings - ie rings for an .020 oversize bore used in a standard size bore. Such rings will not seal properly; the rings must be correct for the bore size - .020 over, 030 over...whatever.

If you are really interested in accurate info re gapless vs standard rings, do some searching on unbiased sites - those that have no interest in whether you buy that type of ring or not. Note that most magazines (real or on-line) are biased toward any product they advertise. I have seen and (sadly) participated in dyno testing that, in a magazine ad was, if not exactly lyin', it sure wasn't truthin'

Britstuff said:

Hi Marshg246:

Thank you for your comments. You got me looking closer at the red and green markings on the oil control rings. Referencing the "UH-Oh" thread they should look similar to the following:

Not:

I think the left piston oil control ring may be installed incorrectly as above? Please see pictures below. Note the green portion is not visible as it is presumably beneath the red. The overall circumference of the left oil control ring seems to be less than the right. I wonder if this is the core of my issue?

Click to expand...

Your left piston pic is a little fuzzy to be sure, but it certainly looks to me like the spacer ends are overlapped, and not correctly fitted. You should be able to see the difference by eye when comparing the two pistons. If that is the case, it's not the rings' fault that the mechanic installed them incorrectly. If that's the case, all you need to do is remove the rings and re-install them with the oil ring spacer properly aligned. No need for new rings. Running them this way shouldn't have damaged them.

Installing the spacer with the ends overlapped instead of properly butted together is pretty easy to do. I've installed a lot of ring sets, and it's a mistake I've made a couple of times. Fortunately for me, I only installed a piston that way once. After that, I always checked oil rings with this style of expanders again after installing the rings, and was able to correct any mistakes before installing the pistons. It's a mistake that's pretty obvious if you look at it closely.

Ken

@Britstuff , I agree with Ken. From the pictures you posted it can be seen that you have the type of ring shown in the second image below..



Now compare that to the picture of the suspect ring in your picture (rotated for clarity), and you can plainly see the abutment on the red side, but the "hump" (for want of a better word) on the green side is right up against it. So either it is simply overlapped, or the end of the green side is not there for whatever reason. I would inspect it, and if it is there do as Ken suggests.

Looks like you have a good suspect. Was going to state my 850 smoke for first few hundred miles after rebore to 20th over. So your issue at only 100 mile might just need more bedding it time. My bike now has some 5k more miles, no smoking.

Thank you all for your comments.

I apologize for the poor quality photos. I thought they were O.K. but of course I had already looked closely at the pistons and should not have assumed everyone could see what I had already seen first hand!

The pistons are as suggested by "Cliffa" above. Looks like the right hand one was correct but the left hand piston the oil control ring is overlapped at the end.

I did wonder if I needed to run the bike a bit more for the rings to fully bed in. However, I was worried a wrist pin circlip had come loose and was scoring the left hand bore. In the absence of a borescope or similar to check, I decided to pull the head and have a look.

I am rather looking forward to having a chat about it with my mechanic friend. He is a top notch old time engineer who has, (as the old saying goes) probably forgotten more than I will ever know. Delighted I might actually have one over him for a change!

Cheers,

James

Britstuff said:

Thank you all for your comments.

I apologize for the poor quality photos. I thought they were O.K. but of course I had already looked closely at the pistons and should not have assumed everyone could see what I had already seen first hand!

The pistons are as suggested by "Cliffa" above. Looks like the right hand one was correct but the left hand piston the oil control ring is overlapped at the end.

I did wonder if I needed to run the bike a bit more for the rings to fully bed in. However, I was worried a wrist pin circlip had come loose and was scoring the left hand bore. In the absence of a borescope or similar to check, I decided to pull the head and have a look.

I am rather looking forward to having a chat about it with my mechanic friend. He is a top notch old time engineer who has, (as the old saying goes) probably forgotten more than I will ever know. Delighted I might actually have one over him for a change!

Cheers,

James

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He might be red/green colour blind and missed the overlap.