Ring Gap Mercury 2.5 - ProMarine Pistons

[SAMMYBOY]

I have a question, I'm rebuilding a 96 2.5 Mercury, I'm using new pistons and rings from ProMarine kit #2500P&S.
I'm using an old piston with an old ring as described in the manual to push the new ring 1/2" into the clyinder square to determine the ring gap.
In the one clyinder which has a new sleeve the gap is at the top end of the spec - .025, all the other clyinders are in the .026 - .029 range. This is a fishing motor and longivity in more important than squeezing horsepower.
I have not personally mic'ed each clyinder (dont have an inside MIC, but the machine shop that I used said all the holes are within specs. I did mic each piston as describe in the manual, I'm within the spec for the pistons.

Is the ring gap range of .026 and 0.29 ok? If I installed them using the .026-.029 gap would this create a higher than normal reading during a leakdown test? Wouldit be better to use .010 oversize rings and file them down to spec of .018-.025?

Thank You for your replies..... :)

[Propelled Marine]

Pro Marine recommends 4 to 5 thou. for each inch of bore.

[TB21]

If its just a lake running or fishing engine just put them in and run them as they are they'll be fine.........on a race engine i'd run .004" per inch of bore diameter for the top ring and .0025" on the bottom ring because it see's way less heat than the top ring . And when custom file fitting over size rings don't forget to check the locater pin gap for clearance for it can be very mean to the locating pin. TB

[Superdave]

Be sure to remember to use a small hone to remove all the sharp edes from the ring ends. If you don't the burrs will cause a groove in the cylinder. Also, if you use a 0.010 over ring in a standard bore the ring will have more tesion, or pressure on the cylinder walls, wears out a cast iron sleeve.
Dave ;)

[Jay Smith]

Thats a pretty wide gap Sammy if the bores are not too big due to excess honing or wear! I like .018" to .020" on race motors ( nicom ) and no more than .025" on steel . Might be ok but sure seems wide to me !

Good luck,

[SAMMYBOY]

It sounds like the general consensus - the gap of .026 - .029 is a little too much.

When I started this project, all but one clyinder had the factory cross hatch which I assumed (you know the saying) the clyinders where in good condition.

It sounds like I need to get some facts, as of this posting I'm guessing the holes are within specs.
I will bring the block to the machine shop on Friday and see if I can get them to measure each hole. I will report back the findings.

Thank You all for your input and have a wonderful and safe New Year. :)

[Superdave]

The bore is worn out or tapered. Be sure to have them check several places in each cylinder.
Dave

[SAMMYBOY]

I had the machine shop measure each bore at mulitple locations.
Here is the data (spec = 3.501):
1 3.503
2 3.504
3 3.503
4 3.504
5 3.503
6 3.501 (new sleeve)

ring gap in clyinders (spec -018-.025)
1 .028
2 .029
3 .028
4 .029
5 .027
6 .025

Once again, clyinder 1,2,3,4,5 still had the orginal cross hatch honing.
Here are the recommendation:
Machine Shop - No problem - use them
ProMarine - No Problem - use them
Racer Rick - No Problem - use them

I'm going to run'em with this gap..... I hope I dont regret this decision.
I update the board with leakdown and compression results.

Thank You all for response!!