Offshoreonly.com - compression test

Offshoreonly.com (https://www.offshoreonly.com/forums/)

- General Q & A (https://www.offshoreonly.com/forums/general-q-20/)

- - compression test (https://www.offshoreonly.com/forums/general-q/170292-compression-test.html)

compression test

did a compression test tonight been fighting a to me blowby issue here are the results , first of its a 598 inch 10.1 to 1 dart pro one heads , anyway here are the results , 1 175 2 189 3 191 4 174 5 175 6 175 7 174 8 176 as you see all are really close except for 3 and 4 witch are way higher what would cause this are the rest fading or are the two just that much better test also was on a cold motor i know not the best but my neibors hate this noisy sum ***** . dry to the tips did i say loud !! any thoughts , also can too much oil push my dipstick out as mine will push out after a hrd run thanks rob

Quote:

Originally Posted by ROB FREEMAN (Post 2294325)

Rob:
While your readings are good and consistent, having that much crankcase pressure is not a good thing.
Do you have breathers in the valve covers? Can you feel crankcase pressure at idle from the oil fill hole?

Sometimes long-stroke engines make pressure at high RPMs because they need more or bigger breathers in the valve covers.

Do a leak-down test.

:ernaehrung004:yea i have two ateco going to do leakdown soon i hope waiting to hear back i deffinately crating some crank pressure , im goung to drop one qt of oil and see if this helps the dipstick thing new motor and a little concerned at least thanks for the reply not many ideas out there it seems

A leak down test should be done on the engine warm. Your compression numbers are not bad. Also make sure you have a good crankcase system. On my larger cubic inch engines I run a vacuum pump. They are worth about 40 HP and really keep the engine sealed.

a little more oil on the cylinder walls of thoughs 2 holes could raise the comp check just a bit, but a leak down will tell the story, and No on the to much oil thing, It's got to be crank pressure, I would fix that before all your seals start to leak.

Quote:

Originally Posted by mrhorsepower1 (Post 2298004)

at what size of engine do you recomend a vac pump?

Also what kind of vaccum pump?

I see about 180 lbs on a 510 at 9.75 CR with a 741 cam. I think 175 is good, the 191 is a little high, but unless you totally blue print a engine & the heads they will be off. Ive seen 3-4 cc difference in the heads from cylinder to cylinder.