Hot Cylinder on Two Stroke

[Goggomobile]

Hi all
Trouble in paradise as they say.

While bench testing my 1959 two stroke two cylinder 300 cc Goggo engine ( basically a motor bike engine ) I started getting one hot cylinder. other fairly cool. Significantly hotter only after a few minutes. Very hot after 5 minutes - like spitting hot.

Ive gone thru all of the tests and possibilities and have come to the conclusion it is the little end bearing.

Things Ive checked:

a) Compression 110 psi on both cylinders
b) Inspecrion thru ports and spark plug hole. All looks ok. Not the best way to check but I was looking for anything munched up in the cylinder.
c) Fuel mix - 1:30 using victor two stroke mix and unleaded fuel
d) Spark to plug good
e) Engine sounds ok .. Slight rattle
f) Engine running and sounds ok
g) Turned the crank manually with and without plugs and insects. Again easy to crank nothing unusual.
h) Spark plug NGK AB-7 .. On the cool side for a plug.

I did notice the hot cylinder,s coil getting hot as well. Figure this is unrelated.

Have I missed something ?

Randal

[Gavin Newman]

Any chance of posting pictures of the electrode end of the 2 plugs. Is it single carb or dual carb?
Have you looked for leaks in the bottom end that might be causing that cylinder to be running lean?

[clear out]

The rattle could be detonation caused by lean mix on that cylinder.
How hard is it to take that cylinder head off to check the top of the piston.
H.

[morrisman]

Hi Randal. I'm no expert - but with 2 strokes, the crankcase seals have to be in good condition . With the 2 stroke system, the crankcase is pressurised to some degree , you can test the crankcase for leaks . I have a few vintage chainsaws and they usually need new seals fitted Mike

[Goggomobile]

Hi all
Thanks for the info. I'm back home next Tues. Out in the Wild West visiting family. I'll have a closer look and send thru pics ..

Randal

[Aussie Bruce]

Check for Exhaust leaks at the Cylinder to pipe Joint no two stroke likes leaks at this critical point

[Goggomobile]

I'm back sure must say the weather was picture perfect out west.

ok spark plugs. New plugs. This is after about 20 minutes running.

[Gavin Newman]

Which plug was in which cylinder?

[morrisman]

The lighter coloured one has been running lean , hence overheating . The lean mixture causes a longer burn , which makes more heat .

[Goggomobile]

Pics of head and Pistons below. .. checked clearances etc .. Nothing obvious, all look ok

pic 1 - underside of head cylinder 2 - hot one
pic 2 - cylinder 1,- cool one
pic 3 - Pistons - LH cylinder 2 hot one,
- RH cylinder 1 cold one,

current theory is leaking crank case seal

[Chris Parks]

Pics of head and Pistons below. .. checked clearances etc .. Nothing obvious, all look ok

pic 1 - underside of head cylinder 2 - hot one
pic 2 - cylinder 1,- cool one
pic 3 - Pistons - LH cylinder 2 hot one,
- RH cylinder 1 cold one,

current theory is leaking crank case seal

Do a leak down test before going any further, guessing has blown up more two strokes that I care to think about.

https://www.youtube.com/results?search_query=leak+down+test+on+twin+cylinder+two+stroke

[Goggomobile]

Yep ... Did a test ... Leaking like a sieve .... Cylinder to cylinder and through the seal into the dyno. Lucky it didn't fry the dyno.

Explains the different plug colors and deposits on cylinders and cylinder temps

I started pulling it down today .. Will keep me off the streets for awhile.

Many thanks to all for your help. I give an update as I go.

������������������.

[Chris Parks]

Even after you re-build this motor or any two stroke a leak down test is the first thing to do as confirmation. The job isn't done until it is confirmed leak free.

[soundman]

Just as an aside and nothing to do with the original problem ...... you would be wise to go to a better quality two stroke oil ..... one that is capable of running at 50:1, even if you continue to run at 30:1.

The modern high perfromance two stroke oils lubricate way better and run way cleaner than the old type rubbish they put in mowers.

cheers