Just performed a compression test on a mid 90's model yammie 70 HP 2 stroke. The results were Cyl 1. 120, Cyl 2.115 Cyl 3.108. Are these results ok?
Just performed a compression test on a mid 90's model yammie 70 HP 2 stroke. The results were Cyl 1. 120, Cyl 2.115 Cyl 3.108. Are these results ok?
hi mate i would have to say shes very borderline fair amount of difference there on the last pot are you looking at buying the engine all comps should be eqaul or within 10%of each other di you try runnig it for a while then retesting it
Buying the boat from another location so had a boat mechanic perform the test. Didn't get a chance to run the motor myself. Not sure how the test was performed either. Will need to find out those details i.e. warm motor or cold.
Last edited by Micadogs; 02-03-2008 at 08:01 AM.
hard to tell really, depends on battery quality and other variables, static comp is ok indicator but not totally reliable, was 120 the reading the first and the 108 last?
either way, its not too bad, would prefer to see pressures closer but again, depends on the cranking etc when test performed
ok mate would have to think if a mechanic tested it he would have done it correctly if it were me id be a little shy of it myself i would prefer to see them closer than that like 120 115 115 would be okay i know its not much but giving you a resonably good indication that there may not be that much life left in the old girl
thx
Yea it's too borderline to consider, for sure it would run well ATM. I have the 90 yam same design of engine, the top cyl runs the hottest and the bottom the coolest, it looks carboned up to me, that engine is on the way to snagging/scoring the bore (if not already) a ring in the next 10s of hours or so.
Just for reference my engine is 130psi with no variation to be bothered relating.
cheers fnq
Last edited by FNQCairns; 02-03-2008 at 08:20 AM.
Clee - not sure the order the test results were performed. Does this make a difference? Are the decreasing results are a pattern of some sort. Is there a procedure that I should request the mechanic to perform to confirm results?
I'm Kinda with FNQ I would like to see higher than 125 psi.
However as FNQ says shes probably carboned up, top cylinder the highest PSI cause the carbon gets burnt off better cause shes the hotest pot.
And the lowest coolest cylinder will have the most carbon build up there fore lowest comps. The carbon will be probably behind the rings causing the PSI to be down.
Anyway that motor should have the heads off by now to clean the cooling gallerys, they block up with salt.
But before that give her a good spray tthrough the spark plug holes with carby clean, turn the motor over a few times then spray more carby clean down her let soak for 5 mins then start her up to oil up the bores again.
Then give her another comp test and compare the figures if the same might be best to walk away or offer 1500 bucks less for repairs.
Micadogs im also with fnqcairns mate if i tested that myself i would walk away with those results when you have variences like that it is definately telling you something isnt quite right and is very close to needing some major work the last thing you want is to outlay money then have to put your hand back in your pocket within a few trips what was the mechanics opinion on the test i guess the other thing is are you getting the boat at the right price is the some room to spend some cash repairing when needed and still walk away with a good boat at the right price
cheers
With the input above, I will talk to the seller. The seller is a good genuine guy, he has been nothing but helpful and willing to drive the boat around to mechanics, give the honest results etc. Didn't want to sell the boat without all the right checks being done etc. It's the unknown that we test for, and these results have raised some concerns. I will continue to talk with the owner and see what can be worked out.
Anyone else offer some more insights??
Last edited by Micadogs; 02-03-2008 at 10:33 AM.
Sounds as though you have the makings of a good deal there - at least if you budget for some work right away you are far less likely to hit surprises further down the track.Originally Posted by Micadogs
Minor side step here - RAG, how about an intro to your avatar model???
Good luck with it,
Cheers
RAG, how about an intro to your avatar model???
Yeah she's pretty rough ah.
Got a bloody big mouth slimy and wet, prickly to touch and taste horrible, definately not a keeper.
Micadogs,
They are within 10% so I would not be overly concerned. Ideally a touch closer to one another is desirable but those numbers would not concern me.
Re, the lower comp numbers overall, this is quite desirable in terms of running on poor grade fuel. The higher the comp, the more susceptible to burning pistons.
Most V6 engines run about 100 psi comp.
I would buy that engine and I would also fit that to one of my customers boats and warranty it as well.... (Of course provided it ran well etc etc. I'm commenting only on the compression numbers)
Cheers
agree with BM figures are just within spec, and may last for years, but may also crap itself first time ,that is what second hand is, the Motor is not new, and some TLC and maybe a decarb (even though I am not a big decarb fan) may work wonders.
Hey Micadog,
Often a slight variation in compression can be attributed to sticky rings - esp in a motor that has sat for a while. Usually a spray in through the spark plug ports with CRC or WD40 does the trick.
Even if you have to remove the head and de carbonise or deglaze the bores and replace the head gasket - it's a pretty easy job and possibly one you should think about doing (or having done) in any case. It's pretty easy to clean out the cooling galleries/channels and replace the thermostat at the same time.
That way you know all is OK with the top end of the motor. - You can't put a price on peace of mind.
Regards,
Mark
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