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SUBJECT: # 26377: 1992 Evinrude 175 hp -- Compression?
Submitted by Rob (66.82.9.19) from VIRGINIA on 2/29/04 9:33:00 PM
I have been talking to the owner of a 21' Privateer powered
by the above motor. As he lives almost 600 miles away, we have been exchanging phone calls and e-mails with pictures for a couple of weeks; I've been looking for this hull and the price seemed reasonable, if the motor checked out.
He had a compression check done on the motor earlier this week, and the readings were as follows (cyl # is followed by reading): 1 - 105; 2 - 105; 3 - 100; 4 - 95; 5 - 100; 6 - 90. He e-mailed this afternoon to let me know that a shock treatment with Seafoam had done little to improve the results. His mechanic apparently doesn't believe in doing leakdown tests, by the way. My OMC manual (I already have a '93 140 hp Johnson Oceanrunner) deosn't give compression specs for any of their motors, so I'm at a loss. Obviously, the variation in the readings is a concern.
What should the readings be, ideally? Is the motor something I should walk away from?
- 2/29/04 11:23:00 PM
Submitted by
Sal DiMercurio (68.122.194.88) from CALIFORNIA says Hmmmm.
I'd be concerned about #6 hole, as it's 15 lbs below #1 & #2,....I normally allow up to 10% which would be 10 lbs The bottom cylinders on both sides { #6 # 3 ] seem to be the ones that crap out from what I've seen. I'm sure Seahorse or dunk will give their opinion. Sal
- 3/1/04 11:07:00 AM
Submitted by
Phillip T (68.240.125.121) from TEXAS says Compression
I am in total agreement with Sal. Too much variation between the cylinders. 10% is considered the max by most, I would think that 15lbs. difference is too much. Mosy of the manuals will tell you that the variation between cylinders, not the actual numbers is more important.
- 3/2/04 9:50:00 AM
Submitted by
Roby from TEXAS says Leak down test
Leak down tests are only beneficial on 4 stroke engines. They allow you to pinpoint the cause of low compression such as worn rings, or burnt or sticking intake or exhaust valves. Since the two stroke has no intake or exhaust valves the piston and or rings (cracked sleeve) are the only mechanical cause of low compression on a two stroke.
- 3/2/04 7:24:00 PM
Submitted by
Sal DiMercurio (68.122.118.159) from CALIFORNIA says Roby
Your right, but thats normally what goes out on a 2 stroke, the rings, & a leak down will tell you if their bad. A leak down test on a 2-S is mandatory in my book. Sal
- 3/2/04 9:41:00 PM
Submitted by
Dunk75 (68.44.136.197) from NEW JERSEY says On The Flip Side...
Those compression numbers are not all that bad for a 12 year old engine. 100lbs is about where it should be. That 140 looper will have lots more compression than the V6 will.
- 3/2/04 10:30:00 PM
Submitted by
Alex from GA (24.197.153.184) from GEORGIA says Roby.
Leakdown tests are commonly done on 2 smokes also. Besides the rings there are crankcase seals that you need to check.
- 3/3/04 8:31:00 AM
Submitted by
wcl (24.199.182.214) from NORTH CAROLINA says privateer
FYI There was a change of ownership/management at privateer in the 80's??.....The old boats were good, the newer ones (I think Radcliffe is the name)are the boats that have given Privateer it's outstanding reputation for quality/tough boats. If you call the factory they will tell you what's up. Both the 21' models look good...you are lucky to find a used one at all...much less for a reasonable price. Good luck.
- 3/4/04 9:55:00 AM
Submitted by
Roby from TEXAS says Leak down test vs crankcase pressure/vacuum test
That is not a cylinder leak down test. That is a crankcase pressure or vacuum test. The post was asking about cyl. compression readings. A cylinder leak down test is performed by applying compressed air to the cylinder. This forces the piston to the bottom of it's stroke. In a 4 stroke engine this test is done with both valves closed which is at the beginning of the compression stroke. On a two stroke both the exhaust and intake ports are exposed at the bottom of the stroke so it is not possible to read the percetage of leak down past the the rings. I suppose you could prevent the crank shaft from turning and keep the piston at mid stroke above the exhaust port and take a reading in that manner. But why bother if you have low compression you either have bad rings or a hole in the piston. The leak down test can't tell the difference.
