Compression Tutorial? My first post

Hi, I'm new to the group. I just got my second nonworking KZ250 (one's an 80 and one's an 81) and I'm about to start trying to make one runner out of the two.

I found the following list in the archives, and I confess I'm wholly ignorant of how to perform a compression test. Do you have a tutorial for a "new" bike overhaul to get it running, including how to do a compression test? (when I say "wholly ignorant" that's what I mean -- I know nothing!)

Thanks,
Chris in Kansas City

List from archive:

Re:starting a restoration -2005/12/06 09:56 Here is a generic rebuild procedure (good for any KZ). Search this forum for more detail on each specific item.

1) Check valve clearance and adjust if necessary. Do this first as it could affect your compression. While you have the valve cover off, may want to inspect cam chain and cam chain timing.

2) Once valve clearance is in spec, check engine compression. If compression is bad you have a different set of issues and may want to reconsider if you really want to restore the bike or not. The rest of this procedure assumes that your compression is good.

3) If the starter will not turn the engine over then troubleshoot electrical system. Charge battery and/or replace if it will not hold charge.

4) Check out the ignition system. First make sure you have good strong spark on all cylinders. Maybe do wiredgeorge's relay coil feed mod. Replace spark plugs. After getting good spark check ignition timing.

5) If fuel tank is rusty inside, remove and clean it.

6) Check fuel petcock operation. Repair/replace if necessary.

7) Install (or replace) fuel filter. Do this after cleaning the fuel tank and before cleaning the carburator.

Remove carburator, dissamble, clean, replace internal o-rings, reassemble & re-install. When cleaning make sure all jets and passages are clear by blowing air through. Replace carb boots if they are hard or cracked.

9) Check fuel level in carb bowls. Adjust if necessary.

10) Check condition of all vacuum lines and caps. Replace any that are hard and/or cracked. (Engine will NOT run well with a vacuum leak!)

11) Start engine! Adjust idle mixture screws and idle speed screw to obtain smooth idle.

12) Sync carbs.

13) Now the engine should be running pretty well. At this point I would change all fluids (engine oil, brake fluid, fork oil) as well as oil filter and air filter. Also a good idea to lube the clutch and throttle cables. You could change fluids as the first step but I recommend waiting until you see if you can get the engine running or not...no sense replacing fluids only to find out the engine is locked up.

14) Now you can start on the chassis. Personally I would just get on & ride for a month or two before beginning any chassis work. Exception would be tires & brakes...make sure tires are good (10 yr old tires need replaced even if tread is good!) and that brakes work well before your first ride. While riding you will likely find that some problems will fix themselves while others will develop.

15) Eventually consider repairing the following chassis items: Replace front fork seals (only needed if they leak assuming you changed the oil in step 13), replace brake pads, adjust clutch, replace rear shocks, repack wheel bearings.

16) After all the above then you can begin polishing, painting, upgrading, etc.

crd... You copied a list of generic bike restoration steps and are probably overwhelmed by the enomity of the task before you. It would be simpler to chew off smaller bites on this project...

The major starting point for you is that you have two bikes to swipe parts from to make one bike. That is good. Since you are a novice and probably looking to get this project on the road in as little time as possible, assess the condition of the engines. Pick the ENGINE that is in the best condition as your basic starting point.

Checking compression on a bike that has been sitting for a long time in a non-run state can be misleading. Go to your local Yamaha dealer and buy a bottle of "Ring Free". Pull the spark plugs and pour about a tablespoon down each plug hole. Go out and buy a Clymer or Factory Service Manual and let the Ring Free sit for at least 24 hours...

I don't know if these bikes have kick starts or electric starts. Before checking compression, with the plugs still out... try turning the engine over by hand. The Clymers will tell you how but essentially you remove the points cover and there will be a 17mm nut on the end of your crankshaft with a smaller nut on its end. You turn the engine over using the 17mm nut. That is what its purpose is. Just see if you encounter any resistance. With the plugs out, you don't have to force the engine over. If the engines turn over by hand, look in the engine oil site glass and see if there is any oil... at this point, it is time to check compression.

Having put the oil down the cylinders, you may get higher than expected compression. The oil tends to seal leaks caused by poor seal of the piston rings. To check compression, either remove the carburetors or hold the throttle wide open and turn the engine over either by kicking or using the starter button. Get a compression gauge that has a rubber fitting that allows it to be "universal" as far as plug hole size. Hold the gauge in the hole tightly and crank engine over. You may need to do this several times to get compression to peak.

Once you know what relative (oil amplified) compressions are, let it sit for another day and repeat. The best engine cantidate will compression readings that are fairly high but also close to one another. I would rather use an engine that has 125-130 than one that has 155-135. The numbers are in PSI and that is what your compression gauge will read.

If you find you own an engine that has decent and consistant compression, at that point, you can start pulling parts to make the best single bike and should ask what the next step should be.