Motorcycle Repair: loss of compression in a 4st engine, valve seals, compression tester

Question
hello chris

i am mike and i own a 4st 150cc single cylinder sohc bike. The odo reads 20,000 .  I have a sneaking feeling that the bike is losing compression steadily. Is there any way to rectify this loss without changing pistons or reboring.

bye
mike.

Answer
Hi Mike.
 Has this been a progressive loss of power or was it all of a sudden?
 Have you done a compression test?
Without doing a compression test, you cannot know what is really wrong with the bike.  It could be a few different things that are wrong, either singularly, or tgether.

These are the easily fixable things;

1)  Valve gap and timing.

2)  Problem with the ignition system (electrical)

3)  Valve seals.

4)  Carbon buildup on valves.

The other things that it could be are;

1)  Bad rings.

2)  Hole in piston.

3)  Scored cylinder wall.

Those, there's not much to do about them except go into the engine and replace/repair.  Scored cylinder walls need to be rehoned or re-sleeved.

Get a compression tester and check compression, then check the 1st 4 things that I listed and let me know what you find.  You will also need (if you don't already have it) the repair manual as it will have all of the specs for testing the various areas of repair on the bike.

Good luck.
FALCON