Compression issues

Hey guys, I'm looking for some insight on a problem I'm having with compression. I don't have a compression tester so I don't know what the exact reading is, but I tried the old thumb test and there isn't much. Here's what happened. This is my second bike, it's an 81 KZ 750 Ltd, and it's my first time working on any. I tore down the top end over the winter to replace the gaskets. I ended up installing the camshaft chain in the wrong position and ended up slamming the exhaust valves into the pistons. They ended up with slight bends so I've replaced all of them. Now that it's back together I'm stuck with this compression issue. At first it was very bad. When I turned the engine over you could from the sound that air was flowing straight trough the cylinders and the fuel was igniting in the mufflers. I ended up pulling out the valve shims and installing the smallest size on all of them and now there is a little more compression and it does not sound like air is flowing through any more. I'm guessing that the valve guides have shifted up and i'll need to replace them. Hopefully someone here has a better idea as I'm at a standstill right now.

Thanks

Judging by the fact that you need to heat the head severely and use small nuclear devices to get the valve guides out, I seriously doubt they "shifted" from the valve being bumped by the piston. Could be wrong.....

From what my foggy memory serves, I think if the guide did shift a bit it would not change the clearance. The clearance is set by the actual valve stem length and the shim, the guide just holds it centered in the opening. If the guide shifted up and down a shade, I don't think it would matter. If it twisted or shifted the valve off the center of the seat it would hose it up big time.

Did you actually measure the valve clearances?

Did you have the new valves lapped in and fitted to the seats?

As for valve sealing, the old trick I used to use was: take the head off, and set it upside down. Mix up some real thin oil by blending some solvent into motor oil. Pour the cylinder tops full (where the valves are) and watch to see how fast or if the oil runs out either into the intake port or the exhaust port. If the valve is not seating tight enough to hold compression, it will leak during this test.

I hope you're right, I really don't want to remove the guides as that sounds like a major pain. I'm picking up a set of feeler gauges tomorrow to check the clearances. The valves looked like they were seated ok but I'll try your oil idea over the weekend to be sure. Thanks.

When you replaced the valves, did you grind the valves and cut the seats, or at least lap the valves to ensure they seat properly?

did you check the valves with a feeler gauge,

If you are going to work on a KZ, you really need to buy some proper feeler gauges and a compression gauge. They are not all that expensive. Sounds like you have no valve clearance. Also, it really sounds like you could use a KZRider member who knows what they are doing to lend you a hand. Edit your profile and put your bike type and location where folks can see it.

I have had two bikes, a 900 and a 1000, eat the cam chain guides and bend over all 8 valves. The 900 was mine and it sounded like draging something over a saw blade when it happened. The other bike I bought that way because I had done that exercise before. No damage to the valve guides, or pistons on either bike. As posted above, you need to buy a feeler gauge and a compression gauge. The feeler gauge is about 5 bucks and the compression gauge is about 20. You might think about picking up a manual too....chris3

i agree with steel. when you changed the valves you should use valve grinding compound. you can see wheather the valve seats or not just with the compound. then check the valve clearance.

Got my feeler gauges this morning. I did not lap the valves in, actually never thought of this. I'll see if I can pick up some valve lapping compound on the way home from work. I plan on working on it all day tomorrow. I'll try and post some updates as I'm going.

So you installed different valves in the head without matching them to the existing valve seats?

Very well could be the cause of the reduced compression.