74'Johnson 6hp compression readings

[fishermanms]

OK, I don't how many of you have not read the other thread I posted in regard to the lil J. 6hp, but that is not important. I'm about to order parts and manual. I estimate parts, manual and shipping to run about $180-$190... I have decided to order them here on iboats because they have everything I need and because I have had loads of help here. My only concern at the present is compression readings I have took. I been taking readings for two-three days now. I am using a cheap lil $20 gauge. The first time I took the readings they were 85-86 top cylinder and 84-85 bottom cylinder. I have since then loaded up the cylinders with PB blaster and took readings today at lunch and tonight. Three times at lunch, three times tonight. They are a consistant 75lbs psi on top and 75lbs psi on top, at least 2 out of the three times each time. They were about 74 the other times top and bottom. So with all that being done and sayed.... I am satisfied with the numbers being so close...But I worry about what some may think about the low readings... I wish they were 100-110 on both cylinders and consistant but they are not. They are 74-75 on both cylinders and consistant. There is no scorching or anything on the block anywhere to make me think it has been hot or whatever. So I need help to decide whether to order the parts or just forget about it....

 

[Joe Reeves]

Re: 74'Johnson 6hp compression readings

Be carefull what you shoot into thoise cylinders as many substances have a cutting base. It would be best if you simply used a fuel/oil mixture as that's what the engine will be running on and lubricated with. You could go slightly heavy on the oil side.

 

[fishermanms]

Re: 74'Johnson 6hp compression readings

Thanks Joe, I was trying to loosen up rings that may be froze up and anything else in there that might be stuck. I read where others have done the same and got results. I need to be careful with the gas too... I heard it has an explosive base. So Admiral ..... Do you have any comments relative to my compression readings??? I would appreciate it. Thank You.. Fishermanms

 

[BF]

Re: 74'Johnson 6hp compression readings

is the gauge the screw in type, or the type you have to hold against the hole? I don't trust low readings off the latter type. Have you checked compression of some other engine to see how the gauge reads? A "75" on your gauge might actually be a 90... maybe check the lawnmower or chainsaw etc, and see what the gauge says there.

anyway, that's my thoughts.

 

[Joe Reeves]

Re: 74'Johnson 6hp compression readings

For the record, a $20.00 compression gauge isn't cheap. ON those small hp engines, 70 to 80 psi compression is about average. It also depends on how fast one pulls the engine over. What you've stated sounds okay to me.

 

[fishermanms]

Re: 74'Johnson 6hp compression readings

Thanks a lot!!! Decision made. I'm ordering the parts in a few mintes. I was gonna do it anyways ... But that really helped. I appreciate your comments.
Fisherman... And by the way, back up a couple of threads.. I will check my compressor gauge on some of my other motors. Theres a 140 Evinrude sitting on the back of a Bumblebee that I put a new powerhead on in 1981. And I'll have a few chain saws and Cub Cadet... Fishermanms