1994 Mariner 115 2-stroke Compression/ Engine Work?

runabout367 · #1 June 27th, 2009, 05:27 PM

Hello,

Im looking at a used boat and had a compression test done on the outboard. Results came back as 142, 140, 143, 145, are these too high? Numbers are very consistent which is good.

joeyplumley · #2 June 27th, 2009, 06:46 PM

I don't know if anyone's ever been worried about their compression being too high (unless they've shaved the head or swapped pistons). You're looking for similar readings across all cylinders, which you have, so I'd be happy with the results.

runabout367 · #3 June 27th, 2009, 10:52 PM

Ive heard numbers should be in the area of 125psi, I dont have much experience in outboards, would you say there would be something to worry about?

joeyplumley · #4 June 28th, 2009, 02:47 PM

Have you tried different gauges? I've tried 3 gauges - they all read 10 psi off from each other. So, it's possible you don't have 140 psi, but maybe something less. Again, another reason why you're looking for consistency between cylinders instead of actual numbers.

I wouldn't be concerned about the reading you've taken. If you're not convinced, try a different gauge and see what you get.

BTW, 140 psi is roughly 10X atmospheric pressure, which means a comp ratio of 10:1, which is fine for pump gas. If you really concerned about predetonation, run high octane.

runabout367 · #5 June 29th, 2009, 03:17 PM

I had the engined checked out by a local dealer/shop, they ran all the tests, not me. I called another merc dealer and they said 150 for compression is standard. So the compression sounds good, but I was also told by the shop that the lower unit is leaking internally and all the seals need to be resealed/replaced, quoted me for 750 with a new water pump, this seems extremly high to me. Am I getting ripped off, because i show limited knowledge to the service dept?? He also said it is also running rich and the carbs need to be rebuit along with a tune-up, quoted 1250 for that!!

I was told its a good motor, but needs some minor work, 2000!!! doesnt seem minor, what kind of pricing does this type of work go for, is this normal??

joeyplumley · #6 June 30th, 2009, 01:11 PM

Sounds high to me, but I've never taken a motor to a shop.

My dad had the lower end seals replaced w/ new water pump on his '95 Evinrude 48. The shop charged him $350, which we thought was fair. If you're skeptical, ask to see the lower unit's oil. Leaking seals means water's getting in and mixing with the oil (not good) and the oil will be milky looking. If the oil looks OK, ask him why he thinks the seals need to be replaced.

As for the water pump, it should be replaced every year or so, or at most 2 years. They're cheap, and will save your motor from overheating due to lack of cooling water (subsequently ruining the engine). Changing them is preventive maintenance.

Ask him why he thinks it's running rich. Carbs usually run lean when they're gunked up, since jets and passageways are plugged with varnish. Only thing that I can think of that would give a rich mixture would be the bowl float height, which is adjustable, or the float's needle valve won't close off due to gunk in there.

You can always say "thanks, but no thanks" and get another shop's opinion.

It may be worth your while to invest in a manual. At least then you can investigate what they say is wrong and sound somewhat informed when you talk with them. You'll also know how difficult the quoted work will be. Spend the extra money and get a factory service manual, usually found on ebay on CD for around $10.

runabout367 · #7 June 30th, 2009, 04:12 PM

thanks joey for the advice, im going to take a final look at the boat very soon, and maybe pull the trigger after talking to another merc dealer about the problems, they quoted me a rough estimate for under a grand! I think the other place is trying to pull a fast one on me ( the service guy would just keep things short and just say, "well whatever the mechanic wrote down"), might be storing the boat their, so I will keep my mouth shut. I am going to pick up a manual and get a better understanding of things.

sschefer · #8 June 30th, 2009, 05:28 PM

Okie Dokey, if you are NOT leaking L/U lube out your prop, you're being ripped off by your mechanic. The parts for the lower unit should run you no more the $50.00 (seal kit and impeller). You need to order the seal kit and the impeller separately because the impeller kit does not include the shaft seals for the drive shaft or the shift shaft. You can also order the complete water pump kit (around 45.00) and you'll end up with some duplicate gaskets because you still need to order the seal kit. I got mine from Sierra vs. Merc and they're fine. I went to www.crowleymarine.com and get the part number and then ordered the parts from West Marine because crowley was out of stock.

I'm a novice at best and I can do that job in 1.5 hours. At 90.00 an hour for labor you should not pay any more than 250.00 for the entire job including L/U lube.

As for compression, whoever did the test did it wrong. The correct method is to take the reading after only one full revolution of the piston in the cylinder that is being checked. If you go for more revs, you're readings will be higher and fluxuate. I know this because I have done it on my own engine. If you have a Seloc manual it will tell you to count the revolutons. It's easier to just pull all the plugs and do one cylinder at a time because the starter should disengage when the cylinder being tested comes off compression.

Judging from the readings you've listed, if you test the compression on a single revolution you should come out around 125 psi and even on all cylinders. That's considered very good for an engine of this age.

Running rich. If this engine is a 2x4 (runs on two cylinders up to 1800 rpms then runs on all 4, the engine should be set to run rich. If the only check this mechanic is doing is looking at the plugs then you definitely need to find an honest mechanic.

This engine might be running with perma gap plugs. If it is then they will always have a small amount of fuel/oil on them when you take them out. Your mechanic should know that!

Knowing what I know about the engine from the info you've provided, I would do another compression test, the correct way and if it looks good, buy it.

runabout367 · #9 July 17th, 2009, 01:03 PM

when i took the boat to the dealer, they ran a vaccum test on the lower unit, told me all seals need to be replaced. Had a little lube leaking out, it was drained last fall. I cannot determine whether all seals should be replaced, but sounds like it should be done with the water pump at the same time. I believe the price should i the range of $350 -$450, not $750, seals and pump go for 50-75 and few hrs labor, i would thinnk no more than $400. As far as the carbs, $1250 sounds ridiculous, carb rebuit kit and tune parts should be also cheap, plus approx~4hrs labor, should be in the range of $500-$600. I am a novice at outboards any more advise?