SPRAY WELDING

I have a piston skirt that needs built back up, spray welding sounds good, who does it?. thanks tom

Well after hearing all the pro's and con's of spray welding and trying to get somebody to do it locally I will tell you what I did. I have a 8 HP Titan. Nice Engine except for cylinder and piston wear. Piston slap if you ran it very fast and the piston would flop around and leak compression near the head end.The cylinder was tapered about 14 thou being larger on the head end. Piston clearance was excessive even on the back end. So I ran a Sunnen Rigid Hone in the cylinder untill I got it within a thou or two. Now Mr Piston had 23 thou clearance all through the bore. Cylinder ended up .015 over.

Then I put the piston in the wood stove and heated it to a Dull Red and left the fire die out and slowly cool. I had gained about .007 on the piston. So I repeated the treatment. Temperature is critical. Well Anyway I finally got the piston to fit well. I just finished the last treatment tonight. I will be putting the engine back together in the next couple days and will give you a report.

I had heard old Blacksmiths used to do this when they couldn't afford new pistons for the Model T.

IF YOU TRY THIS YOU ARE AT YOUR OWN RISK !!!! I figured I had nothing to lose as the piston would still be good for a pattern to have a new one cast which was my next plan....

OK, Now you can send the guy's in the White Suits




My Junky Old Engine Page

Now THAT'S an idea! I have a 1 1/2 hp Hercules with a worn piston that was knurled at some time in the past. It's so loose that you can shake it at BDC and compression "gurgles" past the rings. I've used heat to expand or shrink many things in the past, but it never occured to me that you could expand a piston! As you said, what do you have to lose? The piston is no good to you anyway! I'll have to give this a try. George

Had another thought on this...your wrist pin hole dimensions would change due to the expansion, so you might have to ream to a standard size or press in bushings. You might need new oversize rings too. Someone fitted new rings on mine in an effort to stop compression loss, so I'm hoping I can reuse them. Interesting idea and I'm anxious to try this, so please let everyone know how it turns out...good or bad. Thanks! George

Well I was going to give it a try with the old rings as the gap actually isn't that bad. The lower 3 are step gap rings and in the top groove I have 2 rings as I had cleaned the groove up. If things work out well I will then order new rings as I can pull the piston out the back easily. The wrist pin hole doesn't seem to have changed much and still slides through with no misalignment. And I do know one thing.... You CAN Get it too BIG..

Many probably recall that in the "good old days" when an inexpensive rebuild was done, some pistons would be put into a skirt stretcher.

This was an enclosed devise that held the piston securely and a couple of power operated fingers extended inside the skirt of the piston and pushed the skirt flanks out a few thousandths.

The idea was that the piston skirts collapse from running stress, perhaps more than wear, and the stretcher would make them bigger.

These are not cheap looking machines and there are probably some still around. The question would be whether you could find somebody who could still operate it correctly. Just a thought.....

There used to be a number of "piston re-sizing" machines on the market. They worked in different ways, some by peening the skirts and some by heating and stretching and some by knurling. Early aluminum pistons gave a lot of trouble and I think these machines were probably used mostly to reclaim aluminum pistons. I suspect that the heat treatment for old cast iron pistons would be best. I had never heard of it, but it sounds like a good idea. If it worked on Model T Ford pistons, it ought to work great on stationary low speed engine pistons.

Yes, I remember that. It was called Knurlizing (sp) pistons. It was kind of a roller afair and it would leave X tracks on the piston. I think it worked better on Aluminium pistons as they were softer. I don't know what the lifespan of the repair was though.

Actually some old mechanics have told me that sometimes used pistons are bigger than new ones due to the heating / cooling cycles they have been through.

You know, there are a lot of opinions out there and we can digest them and use what we want.

Spray welding used to work great. We used that method sometimes when stroking an engine,we also knerlized pistons to improve cylinder wall lubrication when we built racing engines. Here is somthing else, A friend of mine has a hit & miss engine that someone replaced the rings with high temp O-RINGS. this engine has run for several years now and is still going strong.

Good luck with what ever fix you decide on. Chuck Rich of Central Oregon

In my younger days when I was poorer than I am now I knurled the pistons in my 1938 flat head Harley. I used a bastard cut file laid on the skirt of the piston then hit it with a hammer. Did this several times around the piston. Added some new rings, sanded the cylinder, put it back together and rode it for another year as my daily driver.

We had a piston for a 6 HP Bulldog plasma sprayed. The piston/bore fir was loose as a goose and tapered. We honed the block until we got it straight and had the piston sprayed the thickness of the difference and then some. The piston was turned in the lathe using a carbide tool to a sliding fit. It worked great! I would say it is an excellent option to correct piston slop. The engine runs nice and no noise whatever from the piston or wristpin. Just be sure they mask the grooves and be careful you don't chip the coating when you machine it because the stuff is brittle. We used a place in Connecticut called Metallizing Incorporated but they work mostly on aircraft stuff. They worked it into their schedule as a favor. Ask some of your local machine shops what vendor they use..this process is pretty common. It should cost $100 to $150, but it solves all the problems at once.

Good luck,

Al

We had a piston for a Fuller & Johnson flame sprayed and we bored the cylinder. It turned out to be cheaper than making a new piston, and, the engine probably has more compression than when new! Also, we had no problems turning the flame-sprayed piston to size-in a 1930's South Bend lathe -Nick S

Hi

I have heard about beadblasting pistons with glass beads. The beads peen the metal out to expand it a bit. Never seen it done. Will try to find out more if any one is interested.

Hope this helps

Mac Leod

Well, I had considered Blasting the piston on the inside as I have some coarse blasting sand but figured it would cause uneven stress and I probably wouldn't gain enough. I stuck the Titan back together with the old rings and the piston slap is Gone. Compression is pretty good but could be better but the rings are too small and not seated to the bore. I will order some new ones from Dave Reed in the next day or two. And Yes, I probably would try this Piston Roasting again..

I Talked to Dave Reed about the same problem before he said that he has brazed the skirt of a piston. Just a single bead and turned it in a lathe to the proper dia. top and bottom than side to side to take up piston slap and it does work.

Glass beading, or any media blasting wouldn't yield any significant expansion. Whatever you do gain from blasting, if any, would be tenths rather than thousandths. Blasting however is a good procedure for stress relieving. We put our cast iron engine parts (Conn. Rods, Crankshafts, Blocks, etc.) in our shot blaster which uses steel shot. Anything else that isn't suitable for the shotblaster gets glass beaded. Both of these procedures are mainly used for cleaning purposes but high performance parts (new and reconditioned) will go back through the shotblaster to be stress relieved. Thanks, Jimmy