Cam timing and valve clearances Clearances questio

Okay i checked the clearences and this is what i got:

Intake vlave clearences are .279 .229 .356 .279 all of the feeler guages had a lil more than slight pull.

Exaust clearences are: .279 no clearence no clearence .279

Are these clearences to big on the intake? Also How can I make sure which cam is the exaust and which is intake they are 1985 gpz cams. I am just going through my motor again to make sure everything is okay since it was so hard to start. Also i notice a lil where on where the cam cap goes over on one of the cams is this life threatening or just a slight problem and no need to worry till i can replace.

I am going ahead and setting the cam sprockets bak to original setting since they where degreed slightly and the bike ran cruddy. Thanks for any help i can get!

I was not aware that an engine could even run with compression that low. Are you sure your gauge is accurate? Did you measure compression with the throttle wide open, and all plugs out?

Have you measured your valve clearances? If not, what makes you think they are too loose?

A common symptom of too much clearance is a loud clacking noise coming from your head while the engine is running.

I don't think that excessive clearance itself would cause the compression to drop, unless the reason for excessive clearance is that you have a bent valve, and/or a bad valve seat, so that the valve is not able to come all the way up into the seat and seal properly.

I'd recommend you open your valve cover and measure your clearances. But before you do that, pour a tablespoon of clean motor oil into your spark plug hole, then measure compression again. If it jumps up significantly, then you've got worn cylinders/rings. You could also do a leak-down test that will tell you if compression is being lost past the rings or the valves.

Also, recommend that you put your bike description into your signature. It helps us give better advice if we know what kind of bike you are asking about.

tight valve clearances will cause low compression but not loose clearances.

Yes it does run just not very well, it won't idle on its own. The bike is a 1978 kz650b I have brand new rings pistons and bore. I checked the valve clearences and I just used the actual clearcne size to measure and it slip it out with ease. I did the compression test with no plugs in and also with the throttle wide open. I haven't a clew of what is going on with this bike. It also has gpz cams and carbs. thanks for any more info

double check your cam timing it sounds like it is out a tooth or two.

I have the sprockets slotted a bit but not much also the arrows on the sprockets are straight measured with the top of the head.

Try the oil test, and see if your compression numbers pop up. If so, it's possible that your new rings have not yet seated properly.

I'm still amazed that it will run at all with only 15-30lbs of compression.

there is no way a four stroke will run with 30 lbs it has to have at least 90 lbs for it to fire up something is not jiving here.

I also hooked up a guage to the carb sync holes on the bs 34s and it would not get a proper reading the stick just bounced inside the guage. So i kinda took this as maybe the valves were not opening all the way or soemthing of that nature. Also the bike is kick only sso would this give me some low number on the compression test? thanks!

odl666 wrote:

Okay i didn't think loose valve clearences would do me this much harm. I did a compression test and the readings where low very low like 15-30. The bike is really hard to start but with a lil ether it works. Would loose intake valve clearences also make the bike hard to start and give me low readings on the compression. what are some other symptoms of loose clearence.

The cam timing is way off. Put your hand over the carbs and crank it. It'll blow air back at your hand and won't draw any in. That's the proof. Another test is watch the piston travel down the bore and note the moment the intake opens. In other words normal timing it should start to open about 10deg. btdc. If it doesnt start opening till the piston is near the bottom it's off. When you set it up right do the tests again to verify it's on. Turn it slowly by hand. If you did bend any valves the oil test will show it. Valves arn't that expensive and remember your almost there! When you do eventually get it running, take note of how long the choke has to be on before it will run on it's own, this will indicate wether it's on the rich side or lean side for a jump start on jetting it if needed. Keep in mind that timing might be on now and the valves got bent before u corrected it. The intake should open a couple inches btdc. If it does have bent valves, pull the head and flip it upsidedown. Fill the combustion chambers with water and shoot 40 or more psi into both ports one at a time and look for bubbles. That way you know which valves to replace. It's also good for checking the seal once new ones are in and lapped. Not the end of the world but the beginning of it. Once you get it where their are no bubbles passing through each valve seal it's going to have compression like never before.

going back over things