1976 SUZUKI GT250A - CYLINDER COMPRESSION

[TJCOOL]

wondering what this should be...or a good range and should both cylinders be identical (compression)? ...what is the margin or percentage of allowable difference?
haven't found in my manuals this type of info yet....would like to do a compression test before rebuild...

thanks

TJ

[yeadon_m]

The actual numbers will depend on the gauge used and, to an extent, technique.
I believe 5 kicks with throttle wide open, motor cold, is standard method.
With this, my GT triples return 120-125 psi.
I have read a tolerance of around 5psi is fine (I mean, difference between cylinders).
If its low, it may be difficult to start but I have had motors at 110psi which ran fine.
If its low, try adding a teaspoon of two stroke oil down the plug hole and then measure compression. If the value leaps (say by +10psi) then the bore/rings are worn.
Mike

[TJCOOL]

The actual numbers will depend on the gauge used and, to an extent, technique.
I believe 5 kicks with throttle wide open, motor cold, is standard method.
With this, my GT triples return 120-125 psi.
I have read a tolerance of around 5psi is fine (I mean, difference between cylinders).
If its low, it may be difficult to start but I have had motors at 110psi which ran fine.
If its low, try adding a teaspoon of two stroke oil down the plug hole and then measure compression. If the value leaps (say by +10psi) then the bore/rings are worn.
Mike

excellent..thanks...see..you don't get this kind of stuff in books..testing for worn rings etc...

tj

[Craig380]

To supplement Mike's post, I would recommend testing compression when the engine is hot (that is, 10 minutes or so after a ride). Then the piston / cylinder clearance is as it should be when running normally.

Ignition OFF, throttle held firmly wide open, and kick 7 or 8 times in very quick succession - the cadence should be kick-kick-kick-kick-kick, as fast as you can read those words. Take the reading after the last kick.

If you've got more than 125psi with engine hot, it points to the fact the pistons, rings and cylinders are in good order. More than 130psi is great. 110 - 120psi is OK, but showing the rings and / or bores are maybe getting a little tired, but still serviceable. Under 110 means you should probably think about lifting the head & cylinders and having a look over winter.

[TJCOOL]

sounds like a good idea too...i will be installing new rings and pistons ( I imagine these are still the originals)...as many new parts as I can do on my own....I have teh bike as of now down to it's scivies....next is to have it blasted and painted...

here's another question;

once frame is ready what would be the next best thing to work on and when done install on frame?..I was thinking the complete front end and back end?....first ever restore so a pattern should be followed i guess..

thanks

tj

[yeadon_m]

Each to their own method, but I start with swingarm, mainstand then steering stem, then front wheel, then rear wheel, so its standing, then loom. After that, the motor and all else can be put on when you're ready
Mike

[TJCOOL]

Each to their own method, but I start with swingarm, mainstand then steering stem, then front wheel, then rear wheel, so its standing, then loom. After that, the motor and all else can be put on when you're ready
Mike

ok..makes sense..didn't even think of swing arm...forgot those pieces were going to be separated before powder coating...I should take some pictures as it evolves into a show winner...I have the tank and side panels completed..lovely

if I wanted to test gas tank with the rebuilt petcock installed, could I use water instead of gas?..I have two coats of caswell inside the tank but I figure if the petcock leaks I would rather it wasn't gas...and since the tank is sealed, water wouldn't hurt....I have this strange feeling the petcock may be faulty..

[GTandcbr]

No reason why you cant use water obviously it will have to be completely removed after! The petcocks can be repaired and new internals replaced. See here https://youtu.be/qWNyvjaWfz8" onclick="window.open(this.href);return false;

[TJCOOL]

No reason why you cant use water obviously it will have to be completely removed after! The petcocks can be repaired and new internals replaced. See here https://youtu.be/qWNyvjaWfz8" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

merci GTandcbr...glad to hear that some of my strange ideas aren't so strange after all...will checjk that website