compression check on a 7.5 evinrude?

[merkdawg0084]

Hell, I have a 1982 evinrude 7.5 hp. this motor had a piston seized, I got the piston unseized, but unfortunately it only has about 60 psi of compression and the other cylinder has 90. So i found a powerhead on E-bay. Guy says it has good compression. My question is how can I check the compression before I put it all together? Put a nut on the flywheel shaft and turn it with a drill? Thank you

 

[merkdawg0084]

I need a moderator to delete this post. After thinking it through it's pretty stupid. Thanks

 

[lindy46]

What does he consider "good compression"? Have him provide numbers.

 

[Crosbyman]

step one don't assume.... why not feed some oil, pb blaster atf oil to see if the rings will loosen up give it time and TLc
compression may come up

could be blown head gasket who knows

 

[merkdawg0084]

I haven't received the powerhead from e-bay yet, but he didn't give me numbers on compression? The original motor i bought for 75$ was seized up and had rust on the piston walls. I was able to free it up, but one of the piston walls is rough from where the rust pitted it and it's only giving me 60 psi.My orginal question is before i install the power head to the exhaust housing and go through all the extra work. Is there a way to check compression?

 

[merkdawg0084]

Lindy46 I had already purchased the powerhead from the guy before we started talking compression numbers. He has a very good rating on E-bay so i hope it's ok.

 

[Crosbyman]

As you indicated I guess you could secure the ph & just spin the crankshaft with a drill while taking compression readings

 

[merkdawg0084]

Crosbyman you stated earlier on my original 7.5 motor that I could put pb blaster or atf in the cylinder and let it soak into the rings.. What does that do? Let the rings absorb the fluid and kinda swell up? Never dealt with a powerhead that had been seized. As I said I got it unseized just one cylinder doesn’t have compression.. Thanks

 

[racerone]

Not sure if there is a liquid that can swell up metal piston rings to increase compression- ----Wonderful opportunity for someone to develop it and make a few dollars.

 

[Lightwin 3]

Crosbyman you stated earlier on my original 7.5 motor that I could put pb blaster or atf in the cylinder and let it soak into the rings.. What does that do? Let the rings absorb the fluid and kinda swell up? Never dealt with a powerhead that had been seized. As I said I got it unseized just one cylinder doesn’t have compression.. Thanks

It doesn't do that it just penetrates between the steel ring and the aluminum piston and may loosen any trash that is holding things up.

 

[Crosbyman]

penetrating oils basically break the bond between parts...just lik lossening a stuck bolt

seafoam merc powertune etc... may help