Engine overheating my bike's engine is overheating or is it normal? i have a 150cc bike with 10.6:1 compression ratio. what option do i have to prevent my bike from overheating. thx in advance.

Need to have at lest 90 psi or better

the higher the compression ratio the higher the octane rating required
normal compression ratio 10 or 11:1 will run on 91 or 95 octane rating
higher will require 100-110 octane rating or aircraft engine gas
superchargers only increase the amount of air available for combustion
it is the compression ratio that determines the octane rating required

91 or 95 octane is suitable for 9.5-10.5 ratios ( most engines)
for 12.9 you will find that it runs best on 98 octane
it may be good on 95 octane but generally the higher the compression ratio the higher octane rating
discuss the octane rating required with the bike service agent/service center

150 -170 PSI is Normal You don't want any one cylinder to be less than 130PSI if it is time to rebuild that baby!!
Good Luck.

Hi, if the smoke really is white smoke and is only present when you start then it COULD be just water vapour which once exhausted (after warming up) would result in normal exhaust gas colour from then on.

If it is burning white smoke all the time then it could be piston ring failure. As this is a single cylinder engine you would need to find out what the normal compression reading should be and then check your reading with a compression tester. You probably don't have one but most motorcycle garages should be able to test it for you for a reasonably small fee.

From what I can find out online your compression ratio should be 9.4:1 which means your psi reading on the gauge should be around 124 psi - this may be a little lower due to engine wear.

If you can get hold of a compression tester, make sure you have the bike sized fitting on it (same thread size as your spark plug) and then warm up the engine for a few minutes then turn it off and remove the spark plug. Then fit the compression tester into the cylinder head in place of the spark plug.

Turn the engine over using the electric starter if you have one or the kick start if you don't (it wont run without the spark plug but it will turn over) and note the reading on the gauge of the compression tester. If you have a friend with a similar bike then you can check his and compare it with yours.

Regardless of the reading, now remove the tester and then put about a couple of squirts (teaspoon full max) of engine oil into the cylinder head and then repeat the compression test.

If there is a noticeable increase say 20-30 psi then I am afraid its your piston rings or valve guides which are leaking pressure, the oil temporarily sealed the leak and gave a higher reading.

BUT if the pressure is about the same then its probably not your rings and like I said earlier it could be steam caused by water vapour in the engine burning off at start up. If you smell the smoke what does it smell of?

Hope this helps,

Steve B
UK

Hi
Does this bike have an oil tank (dry sump) which then feeds the engine?

Cheers
Bike-Doc

To test the compression of the engine, use a good screw in type compression gauge. Hold the throttle wide open and rotate the engine through six or seven compression strokes.

The manual says, "If the final readings are 90 psi or more and if the final readings do not indicate more than a 10% variance between cylinders, compression is considered normal".

Do a "wet" compression test as well by squirting 1/2 ounce of oil into each cylinder and redo the test. If the compression comes up considerably, a top end rebuild is probably in order.

At 8.5:1 compression ratio, 120 psi max.

Good Luck
Steve

Taking compression test:- the bike's engine should be at normal running temperature and also tht the throttle should be in fully open position.
Your bike's engine has a compression ratio of 9:4:1
here is a guide frm compression ratio to psi :-
8>1 = 102.9 psi
8.5>1= 102.9 - 110.25 psi
9>1= 110.25 - 117.6 psi
9.5>1= 117.6 - 124.95 psi
10>1= 124.95 - 132.65 psi
10.5>1= 132.3 - 139.65 psi
11>1= 139.65 - 147 psi
11.5>1= 147 - 154.35 psi
12>1= 154.35 - 161.7 psi
Hope this helps!

The engine's compression ratio is probably found in your owner's manual and using that along with ~ 14.7 lbs square inch (atmospheric pressure) will yield the nominal pressure:
If compression ratio is 10:1, the nominal cylinder pressure should be ~ 147 lbs.
It isn't uncommon to find lower pressures on higher mileage engines but none of the cylinders should be over 10 lbs apart and they are typically far less than that.