PUCH 250 SGS

Restoring a barn-fresh 1966 Sears Allstate

Open heart: open wallet

Puch_head_off_pistonsI pulled the head and barrels to see what damage has been done – alas it is the front piston that seized and the rear piston has evidence of oil film loss and scraping. Interestingly these are on the sides that face each other.

I did some research online and it seems that there are four possible culprits:

  • lean jetting
  • low/no oil in mix
  • air leak (causing localized lean/hot spots)
  • timing

I can pretty much rule out air leak and I’m going to go out on a limb and rule out jetting as I believe it is stock.

A mechanic saw the photos and opined that it is most likely timing. This could be so as I haven’t touched the timing since I got the bike. I did reduce the oil to the minimum setting, as I was using modern oils and assumed I could get away with less smoke. Perhaps at open throttle it needs more.

So, clearly a bore or hone and new pistons are in order. The question is why did it seize. I would like to have some confidence in diagnosing the problem before slapping in a new set of pistons and twisting the throttle again.logo_koenig

Clearly this isn’t a unique experience. I found this photo on the net, clearly toasting pistons is a Puch thing. I was hoping to get away with a hone an a set of rings but, clearly, new pistons are needed. So open heart surgery has led to opening my wallet. Those pistons ain’t cheap.

It seems Elko/Konig is the only game in town for replacement pistons.

To think she was so happy just a few days ago….

posted by Fastback in mechanical,parts,Puch,Puch 250 SGS and have No Comments