44 compression

[blueskyracer]

Just curious what compression should be on a 44 Merc..I am getting with a snap-on compression gauge and electric starter readings of (from top to bottom) 115, 115, 117, 120.. Seems low to me and I have way less power the last couple races..

Also is it true the motor is the strongest just before it starts going down hill??

[ricochet112]

Yes, a good fishing motor has around 140 lbs in good condition.

Usually.

[Fihn176R]

120 is usually what you will see if the engine has the keystone two ring pistons.

[mercguy]

Yes, a good fishing motor has around 140 lbs in good condition.

Usually.

HMMM..........not a 44.........

[ricochet112]

It's odd that my worn 25XS with a chrome bore and both A's have more comp than a 44xS, must be compression ratio...

[David_L6]

I would tell you if I knew but I've never checked the compression on my 44... If you start with a good bore, properly honed, put it together right to start with (don't break a ring...), run plenty of good oil, and don't over heat it, it takes quite a while to wear out a Merc.

[mercguy]

It's odd that my worn 25XS with a chrome bore and both A's have more comp than a 44xS, must be compression ratio...

25xs looper.......44xs.....deflector.....

Tim is correct...............you could get more if you "smash" it or special pistons and not meet MIN cc's.....and less if it is high ported...

[Guest]

Compression

Over the years I have done a large number of compression checks. First of all the best tester for the Mercury engines is their P/N 91-29287 which has been available as long as I can remember from Mercury dealers. This is a 0 to200 PSI unit and has a very small internal volumn. If I remember correctly the service info states that all cylinders should be within 15 PSI between all cylinders. Although actual compression is not given the engine should be tested with wide open throttle. Normally a stock engine will produce about 115 to 125 PSI at sea level. As we go higher in altitude this number will drop a bit.

One other note: If this is a race engine porting will play a big part in the compression story. When ports are raised the compression value recorded will be lower!

Alan

[mercguy]

Over the years I have done a large number of compression checks. First of all the best tester for the Mercury engines is their P/N 91-29287 which has been available as long as I can remember from Mercury dealers. This is a 0 to200 PSI unit and has a very small internal volumn. If I remember correctly the service info states that all cylinders should be within 15 PSI between all cylinders. Although actual compression is not given the engine should be tested with wide open throttle. Normally a stock engine will produce about 115 to 125 PSI at sea level. As we go higher in altitude this number will drop a bit.

Alan

15psi difference between cylinders = you have problems........10 and I would question.....

[Guest]

Compression

Only quoting what you will find in the 1963 Mercury Service Manual. From my point of view I look for 3 PSI between cylinders. My four cylinder MOD engines fall in this catagory. We fit rigs to .0045" end gap which is far tigher the the standard Mercury box rings.

Alan

[ram95]

gages vary

Assuming it's a mod'd 44.. what was the compression with your "Snap-On" guage back when it was running good?

Shoot all the cylinders with a dose of Marvel Oil and wiz it over good. Got a waterpump on it? Shoot some Marvel Oil up into it so it doesn't toast itself. Put all the plugs back in except the hole you're checking..... now compare your readings. 120 plus 4 or minus 2 would be okay. Maybe look somewhere else besides rings for your cause of going slow.

my 2 cents

[Larry M]

Most of the time the compression reading on our Mod 44's will read under 120 lbs. Also how it is ported will effect compression which had been stated. I bet our second 44 motor doesn't have 100 lbs while the new one I built which has 120lbs. won't out run a good 80 Yamato!

Larry McAfee

[ricochet112]

Pulled the work order from the 1986 OA586... 45HP 4cyl, which is a 3 ring 44ci, it had 138-147 lbs. I didn't realize that 2 ringer would be so low, with an A being a deflector also and 120lbs is the lower end for our motors.

[blueskyracer]

Very interesting..It sounds like this baby is still in the ball park so I guess I will just go over the motor and check everything..I want to have three motors ready next year with my new one as primary..I just wish I could find the power again in this one.. Time to take a breather

[Guest]

44 Power

If your running a mag I would start with the points. Normally they should be set between .008" to .010". I set to the wider side with new points and to the tighter side with used points. If your not fixed jet carbs then I would also go over the carbs.

Alan