Lehman 120 Piston slap

[psneeld]

I do 6 at 1600, 6.3 at 1700...I rarely go above that.

 

[Comodave]

I have SP225s and we cruise between 1400 to 1600RPMs.

 

[stinkpotter]

Thanks. Single or twins? We were towing a heavy dinghy so we are probably in about the same ballpark. What kind of fuel economy do you get?

 

[NWSeadog]

We do around 7 knts at 1700 RPM with a single 120 in a 34 CHB.

 

[catalinajack]

I finally pulled the head and went after my piston slap problem. Both #1 and #2 were pretty well knackered with aluminum stuck to the tops of the cylinder walls. #1 had two compression rings frozen in their grooves, #2 had one frozen. I used a ridge reamer, not to ream but to gently scrape the aluminum off the cylinder walls so I could get the pistons out. I removed all the pistons/rods, honed, replaced two pistons and re-ringed the other 4. Had the head rebuilt and replaced rod bearings. Rod journals looked excellent. The engine starts right up with very little throttle and doesn't billow smoke like it had. We ran it in for three hours and followed that up with 20 hours of cruising. So far so good. I think I still hear some piston slap, I need to listen to someone else's engine for a reference. But at Least I know what the parts look like in there. I may keep an eye out for a core engine to do a short block rebuild on and have it at the ready.



One question: what rpm do you Lehman guys typically operate at? I've heard 1800 and I know 2500 is the out and out max. We do about 6 knots at 1700 with our single.

We are able to get to 7+ knots at 1,650 RPM with twin 120s in a 56,000# boat using 3.5 GPH.