Piston Problems

[Heartbeat]

Well down here in Fl. no running this weekend.

I broke down my 67 OPS

The piston is brown in the center and slightly pited around the edges, What does this mean? What would cause the pitting around the edges? Also there is pitting on the head around the outside. Could this be caused from to little clearance?

Thanks

Mike

I included the picture but its hard to see the pitting.

 

[Mark Anderson]

Hard to tell in that picture, but detonation or pieces of bearing or glow plug going through the motor would be the first guess. from what I can see I would lean toward bearing.

Mark

 

[Heartbeat]

Bearings look and feel smooth. the small flakes i took out looked to flat.

Thanks Mike

 

[Terry Keeley]

If there are little pieces of metal embedded in the piston try to pick some off with an xacto blade. If it's magnetic it's probably a ball chipping off (even though it "feels" smooth), if not it's plug wire.

 

[gil sonsino]

Typical problem caused by wrong h.c in consequence of bearing failure or bad bushing in the conrod.The brown color in the middle is ok!

Gill

 

[Heartbeat]

Its magnetic, so I will change the bearings.

Also noticed that the needle bearings on the con rod are blued. I know the blued means to hot.

Thanks guys

Would anybody know a good head clearance to start with?

Mike

 

[Scott Schneider]

OPS 67's like @ .012" or so. <_< You can fine tune if you get detonation issues by increasing bowl volume of head. :angry: Don't shim head up higher !!

Also those engine run best on @ 40% nitro fuel with a 20% Oil content.

Scott

 

[EatMyShortsRacing]

Don't shim head up higher !!

well I would shim the head higher to see how much you need to remove from the head bowl..... then shim back down to the optimum clearance with the revised head.....

 

[Don Ferrette]

OPS motors are known for running a little hot to begin with. Check your cooling (water supply) & use large water lines. Watch that too lean needle setting too. B)

 

[Scott Schneider]

:unsure: Quote: well I would shim the head higher to see how much you need to remove from the head bowl..... then shim back down to the optimum clearance with the revised head.....

No No No ~ you may not eat plugs with a higher decking, but the volume increase is not the same that would be equal to amount the bowl is opened up.

As you raise the squish clearance, the engine will actually detonate easier.

If at @ .012" you are eating plugs? Remove head, put into a lathe and remove just a tad of the bowl and try again. In years or racing OPS .67s I never CC'ed a head.

Only adjusted the volume enough to prevent plug from going away if leaned out to far.

To my own credit inspite of not crunching cc numbers was to set a few records, National and local. So this does work and keeps it simple.

:lol: Keep in mind when tuning on the edge, Fuel type and brand, Pipe lenth, prop load must be as consistant as possable. Change any of the formentioned and engine will either start detonating again or won't make max power.

PS. Don is right on the cooling issue, OPS .67's need all the water flow you can give them. As a matter of record my "BEST" engines had .65 Cases. They had factory installed cooling ring around cylinder above Ex port, used the Red water cooled head as well. Major cooling !!

Scott

 

[EatMyShortsRacing]

:unsure: Quote: well I would shim the head higher to see how much you need to remove from the head bowl..... then shim back down to the optimum clearance with the revised head.....
No No No ~ you may not eat plugs with a higher decking, but the volume increase is not the same that would be equal to amount the bowl is opened up.

Scott we have used this way of calculating head bowl volumes and used the result as our midway head volume and then made two more heads - one with slightly more volume and one with slightly less. We have found that the first head has been pretty much spot on nine times out of ten.

 

[Heartbeat]

Thanks everbody

I talked to the guy who sold me the engine, he told me the engine was built by a pro builder (Mark "someboby") and not to fool with the head clearance. I think the bearing failure was my fault (wrong Fuel). When I broke the engine down I did find a leaking rear gasket which was what would make the engine run lean.

Seams like the only way I learn what not to do is after I brake it once or twice.

Mike