Model 28 Vertical - No Compression

[Tiger Small Engine]

This is why we do leak down tests
Lock the engine at TDC Firing stroke so both vales are closed
Remove spark plug and wrap some cloth around a long air duster
Remove dip stick
Insert into the spark plug hole & blow air into the cylinder ( low pressure )
Listen at the dip stick tube , cab & muffler .
You should get a SMALL amount coming from the dip stick and none from the muffler or carb
Spray around the gasket with soapy water and check for air bubbles

A mistake was probably made during assembly.

 

[Humbug]

This is why we do leak down tests
Lock the engine at TDC Firing stroke so both vales are closed
Remove spark plug and wrap some cloth around a long air duster
Remove dip stick
Insert into the spark plug hole & blow air into the cylinder ( low pressure )
Listen at the dip stick tube , cab & muffler .
You should get a SMALL amount coming from the dip stick and none from the muffler or carb
Spray around the gasket with soapy water and check for air bubbles

Thanks for the great advice. I did as you said and applied low pressure air in through the spark plug hole with the piston at TDC. I had the exhaust removed and could feel that air was leaking through the exhaust valve. I pulled the head off again and shone a bright light in through the exhaust port. Sure enough I could see a sliver of light around the exhaust valve. I haven’t checked the inlet valve yet.

The engine ran ok before the broken con rod so either I’ve done something wrong in the reassembly or the con rod incident damaged something else if the valve(s) now won’t close.

You can probably tell that I’m a real novice at this but I’m having fun and learning along the way.

 

[bertsmobile1]

Exhaust vales run yellow hot which is well into the forging temperatures
If the piston touched it when running then the head is most likely bent with respect to the shaft .
Good thing is B & S valves are cheap
Simple test is to pull the head, remove the valve spring and rotate the valve by hand looking for wobble in the valve head .

 

[Humbug]

Exhaust vales run yellow hot which is well into the forging temperatures
If the piston touched it when running then the head is most likely bent with respect to the shaft .
Good thing is B & S valves are cheap
Simple test is to pull the head, remove the valve spring and rotate the valve by hand looking for wobble in the valve head .

Thanks for that. Is this for an OHV engine? Mine has side valves.

I’ve been having a closer look at it this morning and when the piston is at TDC I can see an even gap right around both valves. When the exhaust valve opens the intake valve actually appears to close fully and vice versa. Would this point to a damaged cam shaft?

 

[bertsmobile1]

Because of the nature of the gas flow in SV engines, the valve seat burns / erodes over time
The effect of this is the valve then can not close fully and the fix is to remove a few thou off the end of the exhaust valve
The B & S L Head manual has full instructions on how to do this
When I do them I set the lash at the maximum amount ( some times even a bit more ) .
Sorry about the red herring my fault for not checking the details properly first
The other thing that happens with side valve engines is bits of carbon often get caught under the exhaust valve preventing the valve from fully closing

 

[Humbug]

Because of the nature of the gas flow in SV engines, the valve seat burns / erodes over time
The effect of this is the valve then can not close fully and the fix is to remove a few thou off the end of the exhaust valve
The B & S L Head manual has full instructions on how to do this
When I do them I set the lash at the maximum amount ( some times even a bit more ) .
Sorry about the red herring my fault for not checking the details properly first
The other thing that happens with side valve engines is bits of carbon often get caught under the exhaust valve preventing the valve from fully closing

No need to apologise, I appreciate anyone taking the time to offer help .

I tried grinding about 7 thou off the end of both valves and when I checked again I couldn't see any light around the valve seat. I reassembled the engine and did a compression test - it had risen from 20psi to over 90psi! I dropped the engine into the mower and hooked everything back up and she fired straight back into life again. I was so happy .

I let the engine run for a few minutes then took it for a spin around the garden. It seems to be a little down on power, the idle is low and it struggled with a hot restart. I didn't make any modifications to the carb when working on the engine, I just removed it as a single unit and reinstalled it again. Is it likely that I'll need to tweak the carb settings to get her running smoothly again?

 

[bertsmobile1]