TOPIC:

Willo46... HOW did you check / set the cam timing? Explain in detail. There is no reason for a newly rebuilt engine to run as hot as yours seems to.

Hi WG.

With the cams out, I started by setting the timing to the "T" mark on the ignition timing plate for 1/4 cylinders. Pulling up on the cam chain I made sure it was hooked on the crank sprocket, wasn't slipping back and forth or anything. I then put the exhaust cam under the chain, holding it up and carefully hooking the chain on the sprocket, making sure the arrow mark was pointing toward the front of the motor. I then set in the intake cam under the chain. I counted off 28 pins starting with the one immediately above the arrow mark on the exhaust cam, and set the intake cam to the 28 mark. I then bolted the cam caps on and installed the cam chain top roller guide.

I made sure the arrow marks on the cams were pointing in a horizontal position right at the top edge of the valve cover surface. I then set the chain tensioner. After that I rotate the crank around actually twice and make sure there isn't binding and also that the arrow marks still line up with the head.

Am I missing something maybe??

Thanks a lot!

I'm still inclining to look at the cylinders and pistons. I had two bent exhaust valves in my race bike that went unnoticed till recently that had no symptoms (slight runout showed in lathe when being turned down for shim under bucket mod). Ran 11.04 in 1/4. Might have got a 10s 1/4 with straight valves. Depends on how bent I suppose. The increase in compression after putting some oil in cylinder has me interested. If pistons, bores and rings where tight I would not expect an increase at all. Cylinders must be bored to exact piston diameter. One cylinder matches to 1 piston only idea. If you could pressurize your engine and listen for leaks at intake, exhaust and probably crankcase vent might work. Remove cams first. The only way to check plugs is to run at wide open throttle for at least a 1/4 mile, hit kill switch, close throttle and coast to stop. Pull plug along roadside and check.

You did things correctly as far you you went in your explanation except a couple things are missing. Did you physically confirm you were at TDC for the 1/4 cylinders when you line up the mechanical advance? At this point, you need to really ensure that the cam chain is binding of kinked where you can misread your links later on... like when you install the exhaust cam initially. The bent valve gives me pause thinking there may have been an error at this stage.

I always set TDC... make sure my chain isn't kinked, toss both chains in with timing set using marks on cam sprockets and turn the engine over twice BEFORE bolting anything on. The cams will stay in place and not slip in timing as you do this if you use the 17mm nut on the crank by the advance.

This overheating issue drives me nuts. While I can zero in on the cam timing, it certainly wouldn't cause that much overheating but is something that needs to be talked about. We have quite a number of overheating KZs being discussed and I have personally never had to deal with this issue so don't know what to suggest. I know we have some engine buiders on this board and would like to see some weigh in on this subject... it is very curious to me... Good luck!

I will try to make absolutely sure the motor is at TDC with the timing marks lined up. I borrowed a dial gauge this morning and hopefully can figure out if the piston stops moving at the top of the stroke at the same time the "T" mark on the advancer is lined up.

I will let you know how this goes.

This is driving me nuts too. I have another 900 head I got off Ebay that I might put on. I pulled the valves, and the seats look a little pitted so it might need a valve job on that one too.

Thanks, good weekend to all.

Out in left field Roy once had a dowell to break that holds his advance unit in index with the crank. The said dowell drove Roy nuts. Bike run hot and poorly.
Don't know if this is the problem but just one more thing to look into. Also check the advance unit to see if it is working properly.
If you get a degree wheel use the piston stop to detrimine TDC. Good luck. Roy:silly:

Post edited by: roy-b-boy-b, at: 2006/01/06 13:44

Roy is right on. Check that the little pin that locates the advance isn't broken off. If it is, the whole mechanical advance is sort of in a random position. I would think that if your advance is ON the locating pin on the end of the crank, and you stuck your pinky in the #4 sparkplug hole, that would be good enough for TDC. An exceptionally worn chain can alter the cam timing enough where the engine would run hot or one that isn't tensioned. It would likely slip off but that is something we didn't talk about either. Was the chain replaced? Once you had the cams buttoned down and the idler assembly loctited onto the head, did you then tension the chain and watch it as you turned the engine over. If not tensioned, the chain will bunch up some as it goes over the sprockets. This is how guys who buy an APE style tensioner set the tension...


Roy - I would have called that thing a dowell too but that is spelled wrong and I have no idea how to spell it either bwhahahaha You made an A1 point though!

One last crazy thought... I don't know if you ever rebuilt an engine before and know how hard it is to turn the engine over on the 17mm nut. Did it seem a bit hard to turn? It is semi-possible that one of your low compression cylinders had one of those skinny scraper rings come out when you installed the block onto the pistons and catch a bit... it would have scored the cylinder wall and you could be losing a bit of compression... You could also have broken one of the other rings. Any blow by and was there any undo difficulty turning the engine over by hand?

Post edited by: wiredgeorge, at: 2006/01/06 14:58

You may have just explained why I could not get my race bike to run properly when we first got into racing. Had to pitch entire ignition system to cure.

I will take a look at the advancer assembly when I get home from battling ignorance and poverty.

Another thought, what about the cam chain top roller guide? I put the best looking one I had on but could there be a difference in the one off the 78 KZ1000 head versus the KZ900 head? I was thinking if that is holding the cam chain to a slightly higher height maybe the intake cam is not in the correct location. I will pull them all out tonight and see if there is a difference.

Thanks for all the interest and comments. This is a great forum.

I just remembered something else I wanted to mention. When I was rechecking the compressions and scratching my head, I was looking at the valve clearances written down on a sheet. I noticed that the compressions are in rough relationship to the intake valve clearances.

1. Compression 115, valve clearance .003
2. Compression 125, valve clearance .006
3. Compression 120, valve clearance .005
4. Compression 110, valve clearance .003

Actually I think #4 valve clearance is closer to .0025

I know this could just be a coincidence.

I know I might be saying the same things, but I being chatty tonight... First.. with timing mark on "T"1/4, bolt in the exhaust cam with mark to front, then pull the chain tight from crank (may have to BACK the crank just enough) and put on sprocket (them move crank forward to "T", exhaust cam should start to move at this point), count the pins to mark on intake cam and bolt in cam, recheck pin count, bolt in top roller, rotate engine with 17mm nut a couple of turns forward to "T" and check exhaust mark. I found sometimes when bolting cams with the marks lined up that they get off by a pin because of the slack between the exhaust and the crank being created when the cam is bolted down. The engine doesn't seem to run right then (duh?). CHECK and RECHECK the timing and cams and pins.
Second... Milling the head won't make it run hot, I milled my block .060 to fit the Honda 450 pistons, no problem, in fact felt like it helped.
Third... If cams are out by a pin your compression will be low..and may make it run hot...
Forth... Your cams will advance or retard the same. Crank pulls the exhaust, which pulls the intake, as long as the 28 pin count is right Both cams will be the same. they rotate the same direction.
Remember crank rotates clockwise as looking from point side. And the cam slack is between the crank and the intake
Post edited by: tfh903, at: 2006/01/07 01:17

Post edited by: tfh903, at: 2006/01/07 01:36

Post edited by: tfh903, at: 2006/01/07 01:41

Post edited by: tfh903, at: 2006/01/07 01:43

When i modify cam sprockets on car engines i file or grind away some material from the notch in the cam sprocket where the peg on the cam sets. This enlarges the notch slightly and enables the camshaft to advance ahead of the crankshaft. Inserting feeler gauge or shims into the notch on the sprocket (opposite of the side where i remove material, i have never been able to use more than .012 otherwise the timing will be too adcanced for the motor to run properly. Your case is the opposite where your crankshaft advanced ahead of the cams and now the valve timing is late. It does NOT take much at all and the motor will not build compression. Same goes if your advancing the timing. By simply advancing .010 the motor (a nissan 4 cyl.) will rev like a race car and the tach needle will move up like lightening, you drive the pickup and it feels like u could tow a house but the motor wont rev over 2500rpm. In your case you lose all your compression and such. Just get sprockets and youll get to have some fun setting lobe centers of choice given by people who have known real world info about the resulting pwer curve of a particular lobe center set up. Get Dale Walkers cam video and go for it. You wont be sorry. Check your cam timing on the intake take cam of course, to see if your one notch late. Ive done that on mine and it ran the same numbers as yours and would have run hot when taken on the road and driven.

Post edited by: nads.com, at: 2006/01/07 01:49

Post edited by: nads.com, at: 2006/01/07 01:49