Engine Compression Issues.......??? :(

[j tizzle]

Was wondering how many other Kat riders out here ever had engine compression problems.

I just picked up two Kats.

One is a 1991 600.It has 13k miles.I was told it's been sitting about 10 years.I have the bike stripped down now(just a bare frame w/engine).The compression is:

Cyl. 1) 58 lbs.
Cyl. 2) 140 lbs.
Cyl. 3) 45 lbs.
Cyl. 4) 70 lbs.

The next bike is my 1996 600.It has 26k miles,ran great,alot of power,etc.
It's also stripped down now.The compression is:

Cyl. 1)150 lbs.
Cyl. 2)150 lbs.
Cyl. 3) 70 lbs.
Cyl. 4) 140lbs.

So now what should I do????????????????????????

I'm an auto. tech. familiar with repairing cars/trucks.I've done head gaskets,rings,timing chains/belts before,but never on a bike.
These bike motors are similar to car engines,but different in ways too.I don't have a service manual either.
Are these fun to rebuild?I don't want to screw anything up.
Are parts fairly inexpensive,easy to find/order?
I'll probably need rings,head gaskets,etc.

[HemiKat]

The first thing you need to do it find out where the compression loss is.Is it rings, head gasket or valve issues?A simple leak down test will solve this. The best thing about these bikes is that you can repair the entire top end without pulling the engine from the bike.

If you are an experience mechanic there is no reason why you shouldnt be able to pull the head and re-ring the bike in around 6 hours.

[JimG4652]

After the leakdown test if you tear it down also check wrist pin condition, rod bearings, and mic the cylinders and make sure they're not egg shaped. Unlikely that's the culprit but it's good practice to check it while the engine is apart.

[KAT TOY]

check valve clearances. if ok check after adding a little oil to cyl.

[j tizzle]

Well,I just turned up the amperage on the battery charger from 15a to 225a and the compression is much better now(I'm using just a battery charger/starter,no battery in either bike).

1991 Kat


130 psi
150 psi
140 psi
130 psi


1996 Kat

160
180
100
175

[JimG4652]

I'd still be worried about #3 on the 96 Kat.

[j tizzle]

Yeah that's wierd.

[HemiKat]

Even the 91 seems a bit low. Id much rather see 175-190 on every cylinder.

[scottynoface]

Check valve clearances first, I bet the 93 has some tight azz valves on number 3.

[j tizzle]

When i check the valve clearances,should the motor be at a specific location,or should i rotate,measure,rotate,measure,etc.
Am i looking for the largest gap between the valve and rocker arm?i have some feeler guages,just haven't done this before.

[JimG4652]

http://www.motorcycleanchor.com/katana/trinc/valve.htm

[Kfreak]

You do know that checking the compression on a cold motor is telling you nothing.


Engine at operating temp with plugs removed and grounded, wide open throttle, crank motor over a few times.

[Wolfe_UK]

You do know that checking the compression on a cold motor is telling you nothing.


Engine at operating temp with plugs removed and grounded, wide open throttle, crank motor over a few times.

Not so true.. Doing it on a cold motor can still tell you a degree of differences between cylinders.
But yes, doing it on a hot engine with an open throttle will, on the starter for a few seconds, give an accurate reading.

[Mojoe]

if your second set of readings are accurate, I wouldn't bother tearing anything apart unless you absolutely feel a need to.

I would also bet that you had low readings on the one that was sitting for the last 10 years just because the rings were stuck. try spraying some wd-40 into the cylinders and let it sit over night. then start it up and let it run a bit...take it for a short spin even, then check compression again. if it's better and within specs, then just change your oil (cuz you have wd-40 in it now), then ride it it like you stole it.

[j tizzle]

I'm not tearing either motor apart.I'm adjusting the valves on the '91 because they are out of spec. a little,then I'm just going to restore/rebuild it like it was new.All the parts are in great shape overall,very little to no wear on the cams or anything.

As far as I know,the '91 was wrecked 10 yrs. ago with 13k,and was parked.During the dis-assembly of this bike,I came across lots of bugs,ants,spiders,ear wigs through-out the whole bike and motor.A couple spark plug wells were full of water and debris.The engine itself had a few gallons of old gas/water/oil in it.