Change after shimming

Hello, hope all are doing good. I own an 83 specter 750, last week I re-shimmed because off clearence's (basically, most of the valves had no clearence) and now the bike is burning oil pretty badly. Did I disrupt valve seals? Because the valves are lifting higher, am I hitting worn spots on the guides? Prior to doing this the bike had fantastic compression, so I have sorta ruled out a piston ring problems, however it does appear to get heavier as she gets warmer. Has anyone encountered a similar problem after a valve adjustment? Or maybe other ideas? Thanks

If the valves were tight and now they are correct the seal would not be going onto a less worn on "dirty" area. What might've damaged the seals when the shim adjuster was used to push the valve down further onto the "dirty/ carboned" area. How old is the engine maybe the guides are loose? etc

It is a 1983, with just under 12k miles, it is my suspicion that the shims where never changed, but I also question why i had absolutely no clearance on 5 of the 8 and the other three were nominal. Anyways, thanks for your response and i agree with you, i am going to order some new seals and change em out, it is the more probable cause. If not we will do the guides next. Again thanks

Hi,

Very odd that 5 out of 8 valves had zero clearance at only 12K miles....especially if you never noticed a problem before. Even weirder is that a valve adjustment has caused it to start burning oil.

Maybe check the air filter and air box, and crankcase vent / breather for blockage. Also, when checking valve clearances, I make sure to push the valve lifter (bucket) down and insert the minimum feeler gauge, then release and check if the gauge can slide easily or is tight. Why that way? Because sometimes the lifter isn't down all the way (held to the bore or cam base circle by oil film suction or just stuck in the bore slightly). Really - I've had valves that first appeared like they were too tight actually measure well within specification after making sure the bucket was down properly.

If you do end up pulling the head off for only new valve stem seals, don't forget to check for valve seat leaks using the old solvent in the combustion chamber trick before re-installing the head...

Kray, you are right, it is odd. I purchased this bike last fall as a project. It was laid down some years ago, then sat for a long time. When all the dust settles. I am starting to believe that it might have a slightly bent valve or even two. which might explain why the proper valve clearance is causing oil passage. i was going to just perform a seal replacement, but tomorrow I think i am just going to remove the head and know for sure. Btw, i have been around a working end of many mechanical endeavors but have never heard of "the old solvent in the combustion chamber trick" if you got a moment can you explain, sounds like it might benefit my bike project....Again thanks

Stand the head on one side and fill the ports with solvent, gas, etc and see if the valves leak.
Steve

Mapletree wrote: It is a 1983, with just under 12k miles, it is my suspicion that the shims where never changed, but I also question why i had absolutely no clearance on 5 of the 8 and the other three were nominal.

because nobody ever checked them.

swest wrote: Stand the head on one side and fill the ports with solvent, gas, etc and see if the valves leak.
Steve

Yes, that's about it...spark plugs and valves installed, put the head upside down on a flat surface and fill the combustion chambers completely with solvent (but not something that evaporates quickly - use a high flash point solvent, kerosene or diesel fuel) . Wait an hour and check if the liquid level has dropped to see how much has leaked out, if any. Look for solvent wetting the ports if leaking past the valves. If you can see the level dropping before your eyes, that is a major leak indicative of distorted, bent, or burnt valves.

Note that an untouched used head might have slight carbon or hard deposits build up on the valve faces and seats that will prevent complete valve sealing unless the valves snap closed rapidly as in a running engine - you would see this as a small / slow leak during this test and that could still be o.k.

You should have no leakage on a fresh valve grind / cut if the valves have been properly lapped in.

Mapletree wrote: It is a 1983, with just under 12k miles, it is my suspicion that the shims where never changed, but I also question why i had absolutely no clearance on 5 of the 8 and the other three were nominal. Anyways, thanks for your response and i agree with you, i am going to order some new seals and change em out, it is the more probable cause. If not we will do the guides next. Again thanks

very unlikely it's the guides, very likely it's seals.

bountyhunter wrote:

Mapletree wrote: It is a 1983, with just under 12k miles, it is my suspicion that the shims where never changed, but I also question why i had absolutely no clearance on 5 of the 8 and the other three were nominal. Anyways, thanks for your response and i agree with you, i am going to order some new seals and change em out, it is the more probable cause. If not we will do the guides next. Again thanks

very unlikely it's the guides, very likely it's seals.

Agree about the seals, as I wrote before they are most likely original, by pushing the valve down the carbon on the valve stem cracking (microscopic) the hardened seals.

Carbon can not build up above the seal's on the stem's.

zukdave wrote: Carbon can not build up above the seal's on the stem's.

Correct, my bad.