TOPIC:

How did you check compression? Did you hold the throttle wide open? In any case, the WD40 test where it raises compression means it is sealing the rings. It would be easy to suggest poor hone but it concerns me there is almost no compression at all. I am thinking that if this bike were mine, I might want to do a leakdown test to figure out what is going on before you take things apart. There won't be tremendous compression when the bike is first run but you should have decent compression and the bike should start. Did the bike run on all four cylinders... I would double check things before disassembling again as I just feel there may be something overlooked.

Steell said it twice but you haven't said anything about checking it, so confirm it, check the cam timing again.

Post edited by: OKC_Kent, at: 2006/10/16 10:51

Slightlty bent valves will hurt compression but the WD40 jump in compression confuses me.

Throw some air to it and see if the valves are sealing. Rings will seat from turning the motor over by hand with the plugs out or running it like steel suggested. Place your hand over the carbs one at a time and feel for suction. If the air is forced back out, the rings are not seated. Yet. If cam timing is on the rings will seat. If they dont ill send your a stuffy that you can punch in the stomach. Its mouth will open wide and itll laugh like crazy and say ahhhhaaahhhaaaa..... your rings didnt seet!

nads.com wrote:

Throw some air to it and see if the valves are sealing. Rings will seat from turning the motor over by hand with the plugs out or running it like steel suggested. Place your hand over the carbs one at a time and feel for suction. If the air is forced back out, the rings are not seated. Yet. If cam timing is on the rings will seat. If they dont ill send your a stuffy that you can punch in the stomach. Its mouth will open wide and itll laugh like crazy and say ahhhhaaahhhaaaa..... your rings didnt seet!

Please explain this to me.
My experience with leaking rings is that the blowby will enter the crankcase. How would ring blowby enter the carburator intake system?

i think he meant valves not sealng will push back out through carbs.

Andrew, whenever I send to your yahoo account, it bounces. Here is my answer to you that I had sent offline to your bouncing email addy:

I use RLM Motor Cycle Co. 210-657-0208 address:
123 Remount
San Antonio 78218-3728

Andrew,
I don't really understand what you are trying to do or how you arrived at the conclusions you have arrived at as far as what work needs to be done. On
most heads I work on, I disassemble, clean, lap valves, check guides and then put new seals in place. I don't recut or install new seats...

A valve job is to recut the seats. To cut new seats, three different cutters are used that cut at different angles. Sometimes, if the seats are just
cleaned up, only the last stone cutter is used. Sometimes all three will be used. Usually, this isn't necessary as lapping will improve the seat between
valve and valve seat. This can be checked with special dye. You paint the seating surface and then remove the valve and look for bare spots in the
seat. This stuff is available at most autoparts stores.

What is causing you to ask about this work? Anyway, I am not sure about pricing as I am not sure what I am being asked about. Are seats bad? The easiest way to tell is that if you can't reshim anymore... in other words, the seats are too deep and a 200 shim won't get you the required clearance. If the seats need cleaned up, have you tried lapping? Are the guides any good?

According to my service manual, the compession test is to be done with the engine warmed up, all spark plugs removed, the battery fully charged, and the throttle held wide open while cranking the engine with the starter motor. If you are testing a cold engine, the numbers will be too low because the parts have not expanded.

Some possible causes of low compression:

Cylinder head not sufficiently tightened down.
No valve clearance.
Cylinder or piston worn.
Piston rings bad ( worn, weak, broken, or sticking).
Piston ring/land clearance excessive.
Cylinder head gasket damaged.
Cylinder head warped.
Valve spring broken or weak.
Valve not seating properly (valve bent, worn, or carbon accumulation on the seating surface).

vegasjetskier - Just curious... you noted that "if you are testing a cold engine, the numbers will be too low". I have never noticed an a great difference (more than 10 PSI) between cold and warmed up compression testing. Usually a good deal less. Are you basing your comment on personal experience or quoting a manual? Just curious as noted.

I have never seen a shop manual describe compression testing on an engine that has not yet had the rings cut the hone in the cylinders. I doubt that compression will be all that great but I personally have never tested compression on a freshly rebuilt engine with absolutely no break-in such as Andrews. I WOULD expect that there would be enough compression to get the thing started... as a guess 100 PSI but if anyone has a number from actual testing, I would be curious. Obvious things to check without breaking the engine apart:

1. valve timing recheck (bent valves)
2. leak down to see if it is valves or rings (WD40 test indicated rings!)
3. verify compression test methodology

One of the hardest problems to solve is where someone seemingly did everything right. I know a little of Andrew and he is a real sharp guy and probably did a LOT of research before attempting the rebuild. Wish I were a little closer so I could drop by and lend a hand as he seems to have done most of the stuff right. I still think he should figure out where he lacks compression and ensure that his method for checking compression is right before breaking down the engine again as he MAY not discover where he is getting no compression.

Sorry, i was thinking 2 stroke.

wiredgeorge wrote:

vegasjetskier - Just curious... you noted that "if you are testing a cold engine, the numbers will be too low". I have never noticed an a great difference (more than 10 PSI) between cold and warmed up compression testing. Usually a good deal less. Are you basing your comment on personal experience or quoting a manual? Just curious as noted.

Experience with aircraft engines. Since the manual says to warm the engine up first, I'm assuming this applies to the KZs also. The only real way to know if the compression is correct is to follow the manufacturer's method for checking it. In this case, that means warming the engine first. What I'm saying with the above quote is that the numbers will be lower checking a cold engine, not necessarily that they will be below the minimum allowed spec.

Were the actual numbers ever posted? I didn't see them. Maybe compression's not the issue anyway.

I checked several different KZ's both cold and hot one day, and the average difference in compression was 10 psi.
However I have never done a compression check on a freshly rebuilt motor, never had a need to.