JR3 engine issue -

[1arunem]

Ok, so I purchased a few project carts, one of which has a JR3 engine. It was said to be bad but no specifics given. I have tried to start it and have verified the following..

It spins over well, sounds as it should (no clanks, clunks, knocks, etc.)

It has spark. Plug looks fine, not oil soaked, etc.

Carb is of unknown condition but I tried a small shot of ether as well as a little gas poured in the carb.

With the spark plug out, I can hold my thumb over the hole and it will not push it off. (I need to secure a compression tester).

The breather box does appear to have some oil in it.

Other than seeing if compression is my issue, any other thoughts?

Thanks in advance!

[Spicyunicorn]

Pull valve cover off and make sure valve isn't stuck open and everything is in place

[1arunem]

Ok, new info... got a cheap compression tester and it goes to around 30-40 lbs spinning motor over with S/G..

I pulled valve cover and both valves seem to be moving up and down as they should. Lash is within tolerance..

However, I spun the motor over with the valve cover off and can feel compression coming through the valve area (evident with cover off). Leads me to believe oil in breather was pushed through this area and through the hose leading to the air filter box.

Valve seals/bent valve? What would be the next best logical step? Pull head?

Thanks!!

[Spicyunicorn]

Dump a little oil down the spark plug hole and recheck compression generally if it goes up it's a valve issue if it stays the same it's a ring/cylinder issue

[1arunem]

Will do and report back. If it is a ring/cyl issue would it still have compression coming through to the valve cover area?

[smallblock450sl]

Could be a blown head gasket. Any oil/dirt present around the shrouding?

[meimk]

Originally Posted by 1arunem

Will do and report back. If it is a ring/cyl issue would it still have compression coming through to the valve cover area?

It certainly can. Think of it this way: Piston moving down in the cylinder causes suction in the combustion chamber. With the intake valve open that suction draws in the fuel / air mix. As the piston moves back up in the cylinder and the intake valve closes it causes compression. If the seal between the rings and the cylinder wall is compromised, that compression will be able to push past the rings into the crankcase / oil chamber.

Another possibility is that it's not really compression your feeling. Keep in mind that the crankcase is constantly back and forth between vacuum and pressure: vacuum as the piston goes up & pressure as the piston comes down. That's what provides the "pulse" that makes the fuel pump work.

[1arunem]

Spun it over again and same results with gauge.. Poured some oil in the cylinder and gained about 25-30psi..

[1arunem]

Originally Posted by smallblock450sl

Could be a blown head gasket. Any oil/dirt present around the shrouding?

No oil noted.. Nothing out of the ordinary as far as dirt.

[1arunem]

Originally Posted by meimk

It certainly can. Think of it this way: Piston moving down in the cylinder causes suction in the combustion chamber. With the intake valve open that suction draws in the fuel / air mix. As the piston moves back up in the cylinder and the intake valve closes it causes compression. If the seal between the rings and the cylinder wall is compromised, that compression will be able to push past the rings into the crankcase / oil chamber.

Another possibility is that it's not really compression your feeling. Keep in mind that the crankcase is constantly back and forth between vacuum and pressure: vacuum as the piston goes up & pressure as the piston comes down. That's what provides the "pulse" that makes the fuel pump work.

Didn't think of that. Makes good sense.. I did notice while spinning it over it takes a few seconds before I hear it through the v/c area.