My 3AJ rebuild

[steveloomis]

Check your compression. Should be 150 psi or more. Oil could be getting by your rings. Did you hone cylinder with new rings and check piston to cylinder clearance? Check for oval cylinder? My 1986 usa xt checks at 170 lbs psi. Stock original engine, never apart aside from rocker box reseal and side covers reseal.

I have an 84 xt that smoked after new rings and hone. I pulled it down again and cylinder to piston had too much clearance. Rebored to .5mm, new OEM piston and rings. Now perfect, no smoke and runs great!

[keny72]

Thanks for the tip. I have not honed the cylinder or put new rings as rings where inside tolerance and the cylinder was in really good condition. The head that the engine had had a valve guard loose and smoked as cold but did stop as engine heated up. The head I now have on I did buy from a braker, taken of a running bike. I did have the valves out, clean them and did install new seals, looked OK to me. Now engine smoked as the oil got to the top, so myself I´m thinking the head has some problem, but don´t know. Guess I have to open up and check again. I have a third head from the Tenere #2, it did not smoke oil at all, but had high pressure in the breather tube, pistons rings worn, and valves has bad surface so will need to be replaced.

Have to say this project is feeling a bit ...........But I still wait for the day I will on the road/dirt

[keny72]

To show how much it smokes I did make a small vid clip.

phpBB [video]

I wounder if a bad oil seal betwen head/cylinder can make this? This becorce the smoking seem to start as the bike has run for about 30 sec, as it starts no smoke, and no smoke before it got oil pressure to the head after the rebuild.

[Mezo]

Whoaa, that's not right.

M.

[steveloomis]

Do a compression test. Pressure should be around 150psi or more. Other than valve seals, I do not see how a head can make any difference in oil burning. Always use a new OEM head gasket. If you pull the top end off again, have the piston to cylinder clearance checked. If it is in tolerance then have the cylinder professionally honed to provide a good cross hatch pattern, put in new rings that match the piston, such as OEM piston, OEM rings. I think you will cure the smoke by doing this.

If the piston to cylinder clearance is too great, only choice is to have it bored to fit a new piston. OEM is good, next size over standard is .50mm or 2nd oversize. I have not seen a 1st oversize for the 600's. I just recently did just exactly this and the smoking, oil consumption is gone. Bike is running very strong now.

[keny72]

Ok, folks I will do a compression test, even I do feel the piston/rings/cylinder should be fine.
As I buoght this bike it did smoke som as cold (not close as much as now!) and as warm nearly zero. I suspected worn piston rings then, but eventually found the piston rings was in as new spec (thicknes as gap when in cylinder) and cylinder looked it had have a hone not long ago. Piston was not new, but did look OK, bike has ~70k kms on the clock (73k if I recall correct). Seller did have the bike for about 10 year, did ride around 10k kms whit it and had done nothing aside normal service. The owners before I don`t know of, but after it was imported from Germany, it had change owners fairly fast during a year and a half before the one I did buy it from did buy it. The reason for the oil smoke then was that the intake valve guides had come loose, and been for a while so even the ower size ones was to small. Thats why I got a second head. It seemd OK, but we have to see. I will first do the compression check, the open the engine up again to messuer all. I have a second engine in parts (top only apart) and can also see what mesurments they have. The cylinder do have some scratches and the piston rings seem worn and it has high pressure as some smoke from the breather tube while it was running, but did not smoke from exhaust. Also its valves in the head are bad looking. So I do have options.... I let you know, and toughts are still welcome.

One thing I do wounder a bit, why is all suggesting using OEM bits? Whats wrong whit Prox/Wiseco/Wössner pistons for example? Or Athena gaskets? They are far cheaper than OEM, fits my wallet better. even I have to say I did cheap out maybe to much whit the gasketkit for this rebuild, the cheap ebay gaskets from Poland.

[steveloomis]

My "use OEM" is from experience and from reading of others experience. I am sure there are other quality products out there, but how do you know in advance. I know the OEM are good and strive to use them when ever possible. Use what you can afford. We have an advantage in the USA of buying from Partzilla. Much cheaper OEM than buying from a local dealer and his excessive profit. (I know they have to stay in business and I buy little things from them from time to time and use them for boring and head work).

[scottieh]

Ok, folks I will do a compression test, even I do feel the piston/rings/cylinder should be fine.
As I buoght this bike it did smoke som as cold (not close as much as now!) and as warm nearly zero. I suspected worn piston rings then, but eventually found the piston rings was in as new spec (thicknes as gap when in cylinder) and cylinder looked it had have a hone not long ago. Piston was not new, but did look OK, bike has ~70k kms on the clock (73k if I recall correct). Seller did have the bike for about 10 year, did ride around 10k kms whit it and had done nothing aside normal service. The owners before I don`t know of, but after it was imported from Germany, it had change owners fairly fast during a year and a half before the one I did buy it from did buy it. The reason for the oil smoke then was that the intake valve guides had come loose, and been for a while so even the ower size ones was to small. Thats why I got a second head. It seemd OK, but we have to see. I will first do the compression check, the open the engine up again to messuer all. I have a second engine in parts (top only apart) and can also see what mesurments they have. The cylinder do have some scratches and the piston rings seem worn and it has high pressure as some smoke from the breather tube while it was running, but did not smoke from exhaust. Also its valves in the head are bad looking. So I do have options.... I let you know, and toughts are still welcome.

One thing I do wounder a bit, why is all suggesting using OEM bits? Whats wrong whit Prox/Wiseco/Wössner pistons for example? Or Athena gaskets? They are far cheaper than OEM, fits my wallet better. even I have to say I did cheap out maybe to much whit the gasketkit for this rebuild, the cheap ebay gaskets from Poland.

I second the preference for OEM. With authentic Yamaha parts you know for sure (or take it for granted) that it will work. Sometimes aftermarket tolerances aren't as exacting as the OEM components and can lead to problems down the line. I remember a forum member having trouble with Athena brand valve stem seals leaking down and causing an engine to smoke after it was rebuilt. He bought OEM seals and the problem went away. Also the aftermarket pistons you mentioned may not have the same compression rating and can be too high or low. OEM will always be the same as what came from the factory and that is what is designed to work on the bike. It's kind of like an insurance policy that things will work correctly.

That all being said I buy aftermarket parts for the things that wear down like brakes, sprockets, cables, fork seals, and other external items. But with internal engine parts I try to stick with OEM.

[keny72]

I have measured the compression, first try 130psi, 3 other 100-110psi. Did take head as cylinder off. It do looks like the oil seal between head and cylinder also leaked. The piston was covered whit oil. Exhaust ports dry as primary intake, secondary intake slightly oily / wet all way to carburetor but I think that's normal as it has not been in usage as engine has only had relatively low revs, right?

[steveloomis]

Compression is on the very low end. You may have found your MAIN problem. Other leaks probably just need new seals and gaskets.