Mercury 2.4 225 ring gap? Piston clearance?

**CheckvII** · 09-14-2021, 09:00 AM

Im building a 2.4 225. I found a new old stock block. I ordered a set of pro marine piston kits.. Out of the box the ring gaps all measure .029-.030.. Is this to much gap? Pro marine says they use a different ring material and they can run more gap. I was expecting to have to file them... Im new to 2 stroke engine building so thought i would ask, i don't want to mess up my virgin block lol.. Thanks!

**FUJIMO** · 09-14-2021, 06:31 PM

...welcome to S & F...

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**FUJIMO** · 09-14-2021, 06:32 PM

...you'll have your answer shortly...

**Dave S** · 09-14-2021, 06:48 PM

Who ya callin' .......short

**FMP** · 09-14-2021, 06:57 PM

Reminds me of a thread a while back, wrong pistons ring supplier, went around in circles. Not maybe optimum gap but not going to be a power issue according to some piston manufacturers. How's the bore finished size to piston clearance?

**CheckvII** · 09-15-2021, 08:30 AM

Best i can measure with my standard calipers is bores = 3.376-3.377 , bottom of piston skirt largest spot 3.368.. I didn't have my bore gauge with me, but can get a deeper measurement if needed..

**CheckvII** · 09-15-2021, 09:46 AM

Just talked to Pro marine again. They said there ring tension is different and that .030 was correct"..That it would not affect compression, or leak down. Said it did not matter what the oem merc specs are.. Did they just feed me a line of Sh*t?

**FMP** · 09-15-2021, 10:30 AM

Hahaha... linear expansion of the ring vs bore during high heat soak. Gap probably won't meet end to end and pinch with that number.
It's all about the ring seal and how it seats during break-in , at slow speeds or 6000+ the extra little bit of gap isn't going to bleed off according to them.

**David - WI** · 09-15-2021, 11:05 AM

Geez... it seems like that would be hard on the retaining pins?

**FMP** · 09-15-2021, 12:34 PM

The rabbit hole

**CheckvII** · 09-15-2021, 12:51 PM

I was thinking of getting a set of OE rings and using these pistons, since i already opened most of the ring packs to check them.. I havent measured every piston but looks like the pistons will have about .008 clearance..