TOPIC:

The shop resurfaced my cylinder head to get it flat(ter)when I was having them grind the valves and valve seats during a topend rebuild. I don't know how much they took off but I thought it was a good thing at the time. Since I put the motor back together I have continued to have relatively low compression 105 -125, and the motor overheats. I honestly have checked, rechecked everything, pulling it back apart twice now, cleaned carbs, checked ignition timing, checked the cam marks were lining up right, synced carbs. Nothing I do seems to make ANY difference. After some posts recently about valve clearances, I am back wondering if maybe when the cylinder head was resurfaced, the cam timing is now off slightly, intake retarded, exhaust advanced. Before my wife rolls her eyes at me because I need slotted cam sprockets and degreeing wheel could I get some opinions?

Thanks much all and a good new year to everyone.

I can't see a few thou off the head effecting timing. Unless you have a really really good comp tester I would only use it as a relative gauge between cylinders. I believe a leakdown tester is the proper way to go (pump up with air pressure, attach press gauge, record rate of air loss). Have you tried a bit of oil in cylinder. If comp goes up problem might be in rings. Did you just remove head? Cylinder wall finish is critical to break in and final tightness of motor. Mismatching pistons in bores during rebuild can happen.

Wow...I'll be watching this one closely. I have a head at the shop right now and they also plan on milling it just enough to make sure it's flat. The guy told me it's usually only around .020" or so and it shouldn't make much of a difference (about 1/4 point of compression). One thing for sure though, milling the head will INCREASE compression, not lower it. I'm very curious to see what this could be. Hopefully someone can help out.

what all did you do to motor,and how did it run before you tore it down?your cam chain tensioner should make up for the small amount of material removed to true up head.

Thanks for the replies. The reason I tore it down was the compression was low (100-115), it was blowing smoke and it was REAL cranky to start. Seemed to point to a top end rebuild and seemed like a good winter project.

It had a set of 900 cylinders bored out to 1015. When I checked the cylinders they were worn, right to the wear limit and the ring gaps were too wide (I recall about 30 to 32 thou). I had another set of 900 cylinders so I had those bored out to 1015 and put in brand new rings, the shop honed the cylinders too. The pistons were in pretty good shape still. I test fitted the rings and pistons, everything looked perfect, ring gaps 12 to 16 thou.

The original head that was on it had cracks between the valve seats and the spark plug holes. I got a reasonably good head off a 78 KZ1000, had good cams, no cracks, nothing broken or stripped. That was the head I took to the shop and had the valves ground and the seats cut. I checked all the springs, replaced the valve seals. As I mentioned the shop also milled the surface to true it up. It looked absolutely great when I got it back.

What all did I do to it after that? Well after it was all put together again, new gaskets everywhere, ran it, it seemed like it was running hot, also the compression was pretty low I thought for a rebuilt engine (100 to 120). I also thought I just needed to run it to get the rings seated. Well I ran it but I could only go maybe 10 or 15 miles, and the motor was crackling hot, stalling at idle. It does this every time I run it, I even pushed it to over 20 miles, riding like an old woman and it was still WAY hot. The rubber cam plugs get hot and the ones by the exhaust cam look like they're oozing out.

Thinking I had a fuel mixture problem I pulled and thoroughly cleaned the carbs, set float levels, changed main and pilot jets to bigger ones, replaced the carb boots, new Pingel petcock, fuel lines and filters, synced the carbs with the mercury type manometer (several times)I don't even remember everything I did.

The bike has Dyna S ignition, I checked and rechecked and adjusted the ignition timing every which way, nothing helped. I did the direct coil wiring mod, put in colder spark plugs, hotter spark plugs.

I pulled the cams at least twice, setting and checking the cam timing marks to the book. I checked and rechecked the valve clearances, now all are at 3 to 5 thou.

I pulled it down again over New Years weekend, pulled off the cylinders and head, took the head completely apart, lapped all the valves in, checked the rings and pistons. I did find a bent intake valve so I said "A-HAA", Put a different one in. Put it all back together, same exact thing.

Yep, she's a mystery. Thanks again!

How do the plugs read when you pull them?

I'm also surprised it was running as good as it did with a bent valve. Were you noticed a lot of backfiring when you had the bent valve in there? Did it happen when you were setting the cam timing?

Wow that's a lot of work!! I went through something similar a while back. Do you have an aftermarket rev limiter installed? Once I disconnected the old accel rev master the bike ran beautifully. I spent many hours on cam timing and carb adjustments. I even disconnected the ground and power to the rev limiter and it didn't make a difference. I finally realized that the limiter was shorted internally and the wires going to each coil were still connected, and therefore shorting the coils too. Just thought I'd ask if you had one. Other than that, I can't think of anything right now. Good luck.

I did notice it was "spitting" back through the carbs. However, even with the bent valve replaced it is still spitting back, that's kind of what got me thinking about the valve and cam timing. I'm wondering if the valves are opening and closing at the right points, and I think that would also explain the low compression if maybe the intake valve is closing late (???) i.e after BDC. Would the exhaust opening early explain something too?

I just checked the compression again with the oil in the cylinders and it went up about 5 psi on each cylinder. I have been checking the compression with throttle wide open by the way. I have to think that could just be I haven't run it enough to get the cylinder and rings broken in.

No I don't think I have a rev limiter on it.

Thanks!!

Oh, spark plugs look black but fairly dry, with a tiny bit of brown on the tips, I think the jets might be a smidge too big in it now. They most definitely don't look lean though.

i know this is a pain in the ass ,but check your cam timing again that bent valve has me thinking something aint right with your cams!i dont want to sound like a dumbass but lets go through your cams here!(1)check your timing mark on your points/electronic ignition (2)loosen your chain tensioner,pull your chain off your cams(keep the slack up on chain)rotate your exhuast cam untill the timing mark is flush the top/front surface of head(3)install chain on gear ,starting with the next pin above timing mark count your 28 pins this should line up with the timing mark on your intake cam,(make sure timing marks are on same side intake/exhuast)(4)torque your cam caps down and guide,release cam chain tensioner it should reset automatically(5)turn engine over by hand to make sure nothing goes bump,then set your valves.does this sound like what youre doing?then try your compression test again and see if theres any improvement,then you can move on to your ignition and coils!hope this helps,goodluck happy wrenching!

No problem, I'll check that again, it isn't hurting anything and as long as I don't spend much more money on it I'll probably get to keep it for now. I am also thinking something isn't right with the cams whatever it could be. I have to say it starts right up now, no problems, doesn't seem to be blowing smoke. It does feel to be a bit down on power than I remember from before. I have an oil cooler to put on but that seems like a bandaid, it didn't need one before.

I just like the old buzzard and I'd like to get it running right.