Compression check enough to fry water pump impeller?

[aalbert]

Swapped out my heads for some lower CC units. Did a compression check before, and after, with no hose.

Took the boat out today and I was runnning 15-20 degrees over where I should be (180 at fast idle, 170 at 4500-5000, 145-150 at idle).

I am wondering if the compression check might have fried the impeller, or if I should look at the water passages on the heads for a problem.

Thanks,


Andy

[Raceman]

Are you talking about just spinning the starter for several pulses in each cyl? If so, it wouldn't have hurt the pump.

The reason I ask such a seemingly dumb question is, that somebody on here the other day said he checks his compression by cranking the engine and letting it idle with the guage in one cyl. That of course would fry the pump in addition to being a crazy way to check compression.

[aalbert]

Yes, spinning the motor to do a compression check for each cylinder. Approx 1-1.5 seconds per cylinder.

-=Andy

[crazy horse]

Could there have been something in the heads you just dropped on? Just spinning over your engine with the starter should hurt anything.

[H2Onut]

more compression = more heat = higher temp

[aalbert]

15-20 degrees, even at fast idle (1200rpm)? - that sounds excessive.


The difference in CCs between the heads was only 2 or 3 (from stock down to 35cc), and unfortunately the compression check showed that I must have enough leak by on my rings that I didn't gain anymore than (if any at all) 5 psi..... Our readings were 110psi per hole after the swap (granted the motor wasn't warm.

-=Andy

[rob vaughn]

It should not have hurt it, being in Miami I would bet it's been out before now.... Up here in Ky. mine sits for a spell & the first couple of times out, it runs a little hot... After a spell, it (the motor)cools back to normal...

Try it again, if it continues, I'd tear into it....

[SteveO]

Are the heads just cut or are they a different design? Same thermostats? Do you still have water pressure?

[aalbert]

The heads are stock style heads that were cut, they are not the original heads from the motor however (the originals just finished a series of runs through the dishwasher;)), and I didn't do any checks on whether any of the passages were blocked off before I did the install.

-=Andy

[B.Mac]

It ain't the pump unless it was shot to begin with. 110 lbs with 35cc heads would concern me. Stock heads and fresh seated rings should net you 125 lbs accross the board. 35 cc heads should bump you up to 135-140 lbs.

I would swap the heads back and see if it solves your cooling problem. Then re-check your compression with a different gauge.
If it's still 110 lbs ya may want to think about re-ringing her.
Sounds like she's tired if your gauge is accurate
B.MAC:D

[aalbert]

Just as a follow up, I was back out on the water again today, and had my infrared thermometer with me.... Looks like my indication is correct (overheating, and the gauge is fairly accurate)... Interesting thing with the gauge, was seeing the temp diffference as the water moved through the motor.

Cylinders were around 140-150.
Starboard lower hole - 140-145
Starboard middle hole - 155-160
Starboard top, 160-165

Port - all three holes - 165-170

Ran at WOT and the motor held 180 or so.

I am going to take some fender washers with me tomorrow and see how that does... If it is too cool, I will try going down in size, and once the merc. dealers are open during the week, i will pick up a 120 thermostat.

I still need to do a compression check with the motor warm - my 110 readings were cold (sun was going down and we wanted to button things up).

-=Andy

[Techno]

Were the heads packed in styrofoam stuff for shipping? I've read at least twice that these things clogged a passage. Just one peanut is all it takes.
If they were in this stuff it's probalby worth it to take them off and check the passages.