Hah If only I had one.


Guidelines on finding the top of each cylinder? On a car i put a screwdriver in the cylinder and turn the motor over till it tops out. kinda hesitant doing this on a motor i know nothing about.

Umm yeah I googled the compression after i read the links you dropped. I'm capable of running a search but I'm here to talk to experts that can point me to the correct way to do things not to wade through 50 links trying to find the guy who knows what he's doing.


The bike has no power, the PO said it just lost power when on the highway. I'm doing a coil job and while i'm waiting on the sticks I'd like to see what shape it's in so the first thing i though of was to check compression as that is what i would do on a car engine that was running weak.

 

The easiest way to find tdc without pulling the valve cover is:
Put it on rear stand.
Pull the plugs.
Put the bike in 3rd or 4th gear.
Bump around the tire in a forward direction until you feel air blow out #1 hole.
Put a long skinny object in #1such as a screwdriver or a cut hanger
Turn the wheel until the rod doesn't go up anymore. You have just found tdc compression stroke.
Repeat for other cylinders. Next one on compression is the next in the firing order.

Do the compression test again. If the numbers are low, squirt a litte oil in each hole and test again. If the numbers increase, your rings are bad. If they don't, its in the top end.

 

If you do end up taking off the cover, verify the timing marks. If a cam is off a tooth, it can cause loss of compression and power.

 

I've done several compression checks on older car engines. The engine has to be warm and the carburetor throttle has to be wide open to let air into the cylinder. I also did a compression test on my old Suzuki GS 1000. It has the carburetor piston/needle hooked directly to the throttle cable, so if the throttle cable is wide open, the piston is raised to the top.

Our CBR's use constant velocity carbs. With the engine off, opening the throttle wide open does not raise the piston/needle. That operates off venturi, the amount of air rushing past the throttle plate and underneath the piston. Could the low pressure readings result from the piston/needle and the throttle plate being closed? I would like to see a reading on the same cylinders with the throttle plate wide open and the piston/needle held up with a finger or other mechanism. I am going to get a 12mm adapter to test my own.

 

THX man, This is exactly the info I needed!

I'll see if i can get to it this weekend.


I allowed the engine to turn over for a good 20 seconds so i'm pretty sure It had enough strokes to get intake. I always go a few beyond when the compression tops out. Here's a link to the adapter i got (best price i could find got here in 4 days).

KASTAR 73103 12MM COMPRESSION TESTER ADAPTER | eBay

 

Good point there.

 

I just bought a compression tester and am going to test both my bikes ( 89 and 92 ) when I get the time. Haynes says 177 psi plus or minus 28 psi for the Mk2. My bikes go fine I'm just interested to see what the readings are. I like fiddling......lol. I'm going to do them in conjunction with a carb balance ( when the carbtune arrives ) and a radiator pressure test as well. I love working on these old girls. They are a pleasure to work on and its good knowing you've done it yourself and you know its right.

 

I wouldn't ride a bike any other way Bordo. Piece of mind is so important to me when I twist the throttle or grab that brake lever!

Cheers, SB

 

Got the coil sticks in today so I'll shoot for getting them installed tomorrow and do another test. Had it running yesterday and after fixing the wiring on the old coils it was firing much better and is coming back to life. I'm doing a carb synch as well tomorrow when my Dad gets by with the gauges. Also got the fairings back from the painter today. Lost all the bolts! Dammit I spent hours trying to find them today. I hung what I could with a few spare bolts i had hanging around but i gotta order all new ones. Are there entire fairing bolt sets or do i have to figure what threads i need individually and then order them? Also I still have to get a few fairing pieces to complete the set. This bike was in real sad shape.

upload a pic in a few.

 

Nice colour, your best bet for the bolts/fasteners would be flea-bay(if you want them cheap)