What psi Compression?

[M Strawn]

I just purchased a boat (cheap) with a 1992 Evinrude 40 HP. Model is TE40ELENM and has the VRO system on it. The motor has no compression on the bottom cylinder, the top is 119psi. I would like to know what the normal compression would be for the cylinders for a motor with about 200 hours on it.

The carbs were in synch and the bowls were free from any foreign matter. I did not find any evidence of water intrusion in the bottom cylinder. The only thing I can figure is that oil delivery to the bottom cylinder stopped.

I have purchased a powerhead to replace the toasted one, but I am wondering if there is a way to test the VRO to see if it is working correctly before I install it and run the motor. Anyone have any ideas on other causes of death for this powerhead?

 

[tashasdaddy]

Re: What psi Compression?

i have a 93 40hp i plug the oil hose, and disconnected the no oil sender, and now premix my gas. Mine has around 135 psi compression, i have no idea the hours on it.

 

[Chris1956]

Re: What psi Compression?

Cylinders are damaged by overheating caused by lack of cooling water or too lean a fuel mix, or lask of lubrication. Does your auto oil system mix the oil with the gas before the carbs? If so, then both cylinders received sufficient oil and gas.

 

[Dhadley]

Re: What psi Compression?

Yes, that system - whether it's a VRO or OMS - mixes the oil in the gas before the carbs. Neither system can pick on one cylinder. If the passages in the bottom carb were plugged it wouldn't get gas, therefore it's not getting oil either. Regardless of what the bowl looked like.

However, there are many causes of low compression. If it has none at all it must have been a catastrophic failure. It could be something as simple as the wrong spark plug (burning a piston) to a rod breaking.

You are correct, if you don't find the cause of the problem, and correct it, the same thing may happen to the replacement powerhead. Remember - a damaged piston is not the cause. A damaged piston is a result.

 

[M Strawn]

Re: What psi Compression?

Thank you for the input guys. Dhadly, I will go back and check the carbs more closely. The new (used) powerhead that I got is pristine looking, has 135 psi in both cylinders. I would definitely like to determine the cause of the failure before I proceed.

 

[Gary H NC]

Re: What psi Compression?

Carb rebuilds would be good for piece of mind anyway.That way you can rule them out as the cause.

 

[Dhadley]

Re: What psi Compression?

Complete carb rebuild as well as a complete cooling system service is a standard part of any rebuild / replacement.

What spark plugs were you using? What grade fuel?