Piston Slapping...?

Mark Younggren /

What do you guys think is that tinging the piston slapping the head? It wouldn't run with the mental head gasket so took it off and thing started first pedal and has been running good for a few days.

Re: Piston Slapping...?

Mark Younggren /

Also, will a 70cc hi comp head make any noticeable difference performance wise? I haven't messed with hi comp heads on kits. As of now I am still breaking it in but I am pretty satisfied with the Athena non reed kit thus far.

Re: Piston Slapping...?

Dan (high idle) Conway /

Dude, you gotta get a 70cc head too... the piston is bigger, the bore in the head needs to be bigger too.

Piston slap is something we deal with with mopeds. I have 1,000 miles on a TCCD 70cc kit with a hilarious piston slap. Brand new bottom end and crank, not much play in the wrist pin bearing, good head clearance... just the way it goes on some kits.

You could actually have the piston hitting the head right now, I would STRONGLY suggest removing that head and make sure that’s not the case on a brand new top end.

I would DEFINITELY not ride it til you know what’s going on.

Get the 70cc Low comp head for that kit. High comp is too much compression without a double base gasket or spacer. (This was the case for all the K star/ tccd puch kits i’ve dealt with)

Re: Piston Slapping...?

Dan (high idle) Conway /

PS get a 70cc head gasket too, the 50cc one is much too small for the dome of the piston.

Re: Piston Slapping...?

Mark Younggren /

I do have a 70cc hi comp head with gasket I just acquired. I suppose I could put that on instead in the mean time. What noticeable things happen if you have to much compression?

Re: Piston Slapping...?

Detonation .

This is a 4 stroke piston , but 2 stroke can be just as bad .

Re: Piston Slapping...?

You cant put the high comp head on that kit without adding some spacing for the cylinder. I used a 1mm base gasket and it has enough clearance for a high comp head, I would just be concerned that it would have too much compression.

Re: Piston Slapping...?

Mark Younggren /

Fair enough. Rule of thumb always use the same CC head as your cylinder, but I have ran a couple polini 65cc Puch kits with no problem on 50cc and hi comp 50 cc heads. So it’s not necessarily a must But strongly encouraged, or I got lucky and didn’t have a problem.

Re: Piston Slapping...?

Mark Younggren /

Threw on the 70cc low comp head today and started first kick, but noticed it seems to lack a little power. Nothing crazy but a little less low and high end. Is this to be expected putting a low comp head on reducing the compression to a "safer" number? Also, will the low comp head throw all my tuning off, jet and needle height?

Maxi

15mm bing clone

70cc Athena

biturbo pipe

Re: Piston Slapping...?

Yes, the lower compression may affect some performance but it should keep you from blowing up your engine too soon. You could upgrade your pipe and carb to regain what you lost.

Re: Piston Slapping...?

Mark Younggren /

Fair enough. Thats what I thought, but would I need rejetting just due to compression change?

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