Mercruiser 165 L6 Compression Test results

[david humble]

Have had the compressions tested on Two 165 MERCRUISERS

One engine reconditioned 100 Hrs Ago Showes 150 on all six pots

The Second Engine Shows 70 110 50 110 10 110

HAve been told may just be Stuck valves , is this probable or do you think it could be a larger problem,

going to check valve stems to see if there stuck.

 

[Bondo]

Re: Mercruiser 165 L6 Compression Test results

Ayuh,...

No way of knowing without a Leak-down test....

Either way,.... Motor #2 needs some work....

 

[david humble]

Re: Mercruiser 165 L6 Compression Test results

thanks, as one motor and two legs are in good nick thought it worth tiding up remaining engine, rather than complete repower.

 

[chiefalen]

Re: Mercruiser 165 L6 Compression Test results

I don't know who nick is but, might be just the head needs work.

Valve seats might need polishing. Maybe?

 

[ziggy]

Re: Mercruiser 165 L6 Compression Test results

if yer wanting to know where to look for the poor compression. the leak down test seems like it'd be the ticket. in lew of that. perhaps, just air to test the combustion chamber would lead ya in the right direction... http://www.boatfix.com/merc/Bullet/97/97_25.pdf

or perhaps try a vac. gage. they can be helpful in diagnosis too... http://autospeed.com/cms/A_2393/article.html

google using or interpreting a vacuum gage......

 

[chiefalen]

Re: Mercruiser 165 L6 Compression Test results

Heres the link for a vacuum test.

http://www.secondchancegarage.com/public/186.cfm

 

[david humble]

Re: Mercruiser 165 L6 Compression Test results

thanks, have investigated further, rocker , tappet cover removed,
small leak from manifold, oil on head a bit milky, small bits of metal evident,
removed head , revealed valve stem guides, cracked broken, also area around guides small cracks. valve seats small amount of pitting
Nb this engine is fresh water cooled, with heat exchanger, so rather than go for Recond head looking to have it done up. and replace manifold and elbow.

Also bottom end apears OK

Am i headed down the right path,

 

[chiefalen]

Re: Mercruiser 165 L6 Compression Test results

Maybe, you brought the head to a shop?

What they say can it be saved?

Cylinder walls how they look?

You pulled the motor out of the boat?

 

[david humble]

Re: Mercruiser 165 L6 Compression Test results

head is going to shop for pressure test and quote,
cylinder walls ok,
boat is at mechanichs yard engine in boat.
Boat bertram 25, no need to remove entire engine

 

[chiefalen]

Re: Mercruiser 165 L6 Compression Test results

I only asked if it were out of the boat, than it might have paid off if your keeping the boat, in the long run, to do a mild rebuild.

But to keep costs down, maybe, ill keep my fingers crossed the head can be reworked.

 

[abj87]

Re: Mercruiser 165 L6 Compression Test results

head is going to shop for pressure test and quote,
cylinder walls ok,
boat is at mechanichs yard engine in boat.
Boat bertram 25, no need to remove entire engine

The cylinder walls can still look good with bad rings. did you try putting a couple of oz. of oil in the cylinders and retrying the compression test. If the numbers come up dramatically you have ring problems.

 

[david humble]

Re: Mercruiser 165 L6 Compression Test results

will also replace, Manifold/ elbow, have had mercury outboards for 35 years this is my first I/o.
after reading a bit on Mercruisers , i may be paranoid , but to avoid flooding the engine with salt water through a failed manifold, what else preventativly or inspection wise can be done apart from Flushing after every use, and an annual removal and inspection of the MAnifold. is an annual inspection excesssive.

 

[chiefalen]

Re: Mercruiser 165 L6 Compression Test results

Riser inspection after new, three years.

If still good every year, probably get 5 years out of a riser.

Manifold, on on my boat 23 years and still going.

 

[david humble]

Re: Mercruiser 165 L6 Compression Test results

if your manifold is 23 years old , when do you know when to change it . ie if it suddenly lets go, will you know , before it has let water in to the engine.

or am i overreacting and in reality if the engine is regularly serviced by professional mechanics , should they pick up a potentiall problem ??

 

[david humble]

Re: Mercruiser 165 L6 Compression Test results

have had head rebuilt @half cost of recond unit, new manifold and riser.

popo it back together and find out if thats it ?

 

[chiefalen]

Re: Mercruiser 165 L6 Compression Test results

Hope it works out for you.

Strippers are biting.