WHERE DID IT GO , IM AM WORRIED

To answer your question on pistons and gaskets, Funky, stock head gaskets can be used with pistons up to 77.5 mm. in diameter. (Note to readers: The preceding is based on experience. If you wish to call attention to lack of same, go ahead and contradict it.) Re. valve guide seals, the only seal other than the stem seal is the O-ring at the base of the guide, which can't be seen without removing the guide from the head. I've never seen one of those fail and I can assure you that even leaving the O-rings out entirely wouldn't cause nearly the kind of oil consumption you've experienced.

Anyway, while you're into the motor be sure to check guide to valve stem clearance; I've seen quite a few that were worn out. When there's too much slop between valve stem and guide, the stem seals get wallowed out and fail prematurely.
 
gggGary I think my cylinder head has that "Odd notch "over both cylinders too... so I don't think that is an indicator of anything...
j.s.y.k.......
Bob.........
 
Beg to differ, Mr. Kelly. I can tell you from looking at a whole bunch of XS650 heads over a whole bunch of years that the nasty ding in the squish band should not be there, and I'd suspect that something nasty happened to that motor at some point.
 
hay Griz.....well that is possable Lord knows my memory ain't like it used to be ! LOL
I could'a swore though that it had notches about 1" long on each side of the head just like Twitches !
but maybe it's not...... looked like a machineing mark like perhaps it was out of adjustment on the CNC but sense it didn't effect anything they just used them anyway...that would be my guess.... thanks TM i'll get to reading !
Bob...........
 
Hi every one Thanks for the responses to my issue.
The brown ring at the top of the bores are not ridges just discolouration from carbon diposit as ggg mentioned.
I cleaned and rebuilt the head popped in new valve stem oil seals so thats all ready to go.Valve guides are good where changed during rebuild by SmedSpeed and are made of some space age metal that conducts heat and does not wear very much,, its like Kryptonite but not green more of a golden brown ,,,like the song lol (see picture) DSCN2021.JPG DSCN2018.JPG

I spoke with Smedspeed today after sending an E-mail with photos of the strip down top end prior to cleaning and he was very helpull and like most of us was rather quized about my misfortune.
Possible causation are,,, I washed the bores out when messing with the carbs, the breather system caused combustion threshold to reduce due to oil contamination. He did explain this but it went over my head, verious other theories were put forward by him and myself which would produce excesive wear ending along with defective rings ... The outcome was that the piston rings where the issue after measuring tolerances whilst on the phone, sooo Mr Smedspeed is sending me a new copper head gasket re-usable and Made in the USA and new over sized rings made in japan for me to fit.
The plan is to rebuild top end run the bike in as before, but to disconnect the breather pipes to the air box and run a single pipe to a small receptical of some description to collect any oil if any this stops one possible cause.
He took may mobile and will have further discussions with me and offer further support. what we call in the UK a " Dimond Geezer" im glad i pulled the engine as it all cleaned, de carbonised, lapped, and ready for rebuilding.
So while i am waiting for parts i will be playing with my more modern bike .....

SAY HELLO TO MY LITTLE FRIEND
DSCN2022.JPG
All the best
 
Last edited:
grizld1 said:
To answer your question on pistons and gaskets, Funky, stock head gaskets can be used with pistons up to 77.5 mm. in diameter. (Note to readers: The preceding is based on experience. If you wish to call attention to lack of same, go ahead and contradict it.) Re. valve guide seals, the only seal other than the stem seal is the O-ring at the base of the guide, which can't be seen without removing the guide from the head. I've never seen one of those fail and I can assure you that even leaving the O-rings out entirely wouldn't cause nearly the kind of oil consumption you've experienced.

Anyway, while you're into the motor be sure to check guide to valve stem clearance; I've seen quite a few that were worn out. When there's too much slop between valve stem and guide, the stem seals get wallowed out and fail prematurely.
Click to expand...

Thanks for answering my question Grilzd my bore mesurement is 77.68 what else could i do while waiting for parts, what about polishing the piston heads to minimise carbon deposit has anyone done this????
 
yes it works a treet ! ...
just don't round over the edge of the piston near the rings.
....
Bob........
 
Just want to pass this E-mail I got from Smedspeed after further thoughts and discussion it re affirms that fueling and carboration is so critical .
Many thanks to Smedspeed and great customer support .

i think your main jet is too small, not by much though. maybe one size maybe two . IF it was wildly out when you caned it you would have holed a piston, but just far enough out to make it run hot and to overheat the rings which have gone soft.

i thought about this for ages and its the only thing i can think has occurred

i have emailed my Japanese vendor to request rings and a gasket

Thanks SmedSpeed What a fella
 
Hmmmm, I'd take that with a grain of salt...sorry it's not what you want to hear. Mr Smed might just be recovering ground, from the pictures I've seen it's not been that hot...

Mick
 
Fare enough maybe i just dont know enogh about this sort of stuff . I will keep going lol
 
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+1 re. the salt, Mick; but a grain? I'd take the whole box full! Funky, three points. 1. If the mains were so lean that the motor was overheating till the rings went soft, the motor would have fallen on its face every time you whacked the throttle open. 2. If the motor was getting hot enough to soften the rings, there'd be evidence of at least partial seizure in the bores. 3. Your guy said it himself: heat that high would have caused preignition, and you'd have ventilated a piston. My guess is much simpler, but it takes you where your guy doesn't want to go: oil seep past the head gasket into the combustion chambers due to assembly error.
 
The more i read about this stuff and look into these matters the more I understand. What your saying is probably right. and I appreciate all comments on this forum Thanks.
I have new Pistons,Piston Rings,Gaskets,Gudgeon pins, Clips. Comming from Japan. I have spoken to local Yamaha engineering shop and he said that he will measure my sleeves and pistons,To check the clearance and tolerance which has to be 2 to 2.5 thou I am going to rebuild my Engine best I can thats all I can do.
In for a penny, in for a pound as they say.

I hope with all the forums advise and expertise I will do a better job, No one will be touching my engine bar me from now on.
I cant point the finger as I am not an engineer.But somthing went wrong because my engine developed an issue.
The help and advise received from SmedSpeed is greatly accepted and if he did mess up as suggested, thats something for him to contemplate.

All I want is my bike back up and running and it will be.
What i can say is that I have learnt alot over the last few days about these engines, and that can only be a good thing. Will keep you posted :D
All the best Funky
 
With that great attitude you will win this Funky! Good thing you will soon be able to put that darned Honda back in the shed!
 
Its a sad statement on the integrity of business owners. A "professional" engine builder does a poor job of engine assembly; then blames the owner for using the wrong jets and maybe the quality of the rings as they went soft.
These old bikes should only be worked on by the person that cares....................the owner!
A costly lesson learned.
 
And then, some owners shouldn't even touch their own bikes. The quality of the steel of those rings....now, that could be suspect too. Makes me think of Old Man Honda, one of his first attempts at manufacturing was making piston rings and that failed because of poor quality.

Scott
 
I can't agree with that. Anyone buying motorcycles (or cars and trucks) that are 34 to 47 years old, better have a working knowledge of engines and electrics. If you have to hire people to work on your bike, it will become very expensive, and even so called "professional" mechanics can cause a re-built engine to fail. If you don't have the skills, then you are better to buy a bike that is less than 10 years old, which has a good chance of running reliably, without spending time in a repair shop.

The engine re-builder in this thread, almost certainly used, off the shelf, standard quality rings, that every other shop used for a re-build. The fact that Honda had development, engineering problems when learning to manufacture rings is in no way related to this thread.
 
Thanks gggGary
Some of the reaction from people make feel humble. look people dont worry about others if there good or bad engineers. What matters is what you do, because its you that you see in the mirror. Thats all I know.
All The best
 

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