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Collection, Preservation and Display of Old Lawn Mowers

Briggs and straton fuel fit and lead additive?

Hi folks, 


I have been giving this subject  some serious thought, regarding lead additive for the reason, my old suffolk 75cc cast iron engine had begun to knock and eventually, the bore of the cylinder cracked horizonally. The crack wasnt visible from the outside at all. Only internally and was a large enough crack to lock the engine up immediately. 

I now have a 98cc super punch 17" and the engine feels very tight and.. just from compression and spark can tell this engine is going o be a good unit. 

I'm considering adding a lead additive to the fuel to hopefully prevent any issues with valve seat damage and from my findings, lead in fuel can help to reduce heat hot spots within  the engine which i suspect was the cause of the crack in my previous engine.. hence the unusual crack. 

Next thought is the briggs and straton fuel fit additive. From what i can find, this helps to reduce the effects of the ethanol in u.k fuel and also helps to staberlise fuel. 

I have read that people dont think lead additives are of much use in old lawnmowers as they dont run long enough or rev highly enough. Having owned a few classic cars myelf that required the lead additives, i did find that even sitting at 2k rpm for only 15 or 20 minutes over the course of a few months did result in small but noticeable valve seat recession on a recently rebuilt cylinder head ( didnt want to fit hardened seats) and resulted in being re-ground again. After this using lead additive i found no problems over 3 years and found very little wear after 30k miles. 

It is just my take on things.. what are your thoughts and can anyone rate the fuel fit? Is it worth it?. 






wristpin Sun, 24/01/2016

As you say, Fuel Fit and other similar additives are formulated to combat the adverse effects of ethanol.

As far as valve seat recession / erosion goes I can only speak from personal experience and it has not yet given me any cause for concern but if you are worried about the possibility of damage, go ahead and use a lead substitute additive.  For no particular scientific reason I do occasionally  add a drop of two- stroke mixing oil to my four stroke can.

As far as your internal cylinder crack goes, another forum contributor has suggested that it may have been caused by the hydraulic effect of a cylinder head bolt being screwed into a hole partially filled with oil or debris and your description that the crack is horizontal  does lend some credence to this theory. I Would  have thought that such damage would be visible from the outside of the barrel as well  but  can't come up with a better suggestion.