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Thread: Home made piston rings?
03-02-2009, 02:41 PM #1
Home made piston rings?
Has anyone every made there own piston rings?
What material did you use?
I have a Tecumseh engine Model OHH60 71126C E.
Tecumseh is out of business.
Something is not correct the book says Piston Ring set #40006 standard bore 2.625", $32.00 per set plus $3.20 sale tax. This is 1/4" too small for my 2.8" bore engine.
Piston Ring set #40007 is .010" over size.
Engine cylinder wall mics 2.801" diameter.
Piston ring end gap is .004" x piston diameter.
Hastings Manufacture makes piston rings of all sizes I can order rings by bore diameter and ring thickness no engine model number required. Rings are $5.80 and postage is $7.50. I have ordered the rings they will be here March 4.
I was just wondering the correct way to make home made rings and if anyone had done it?
Last edited by Crash2much; 03-02-2009 at 06:34 PM.
03-02-2009, 03:38 PM #2
The Tecumseh engines have the bore at say 2.5". The piston will have the undersize for than bore so it will be smaller than 2.5" by the clearance the factory deems necessary. The rings will have the tension they require to maintain compression.
When you bore a cylinder oversize you bore the 2.5" to 2.510" and the new piston and rings work in that bore size.
I don't think the .010" oversize rings in a worn bore with the standard piston will hurt anything. You will have to adjust the end gap to the clearance given in the shop manual. I probably still have my Tecumseh manuals.
You can order the rings from Hastings and use them with no problems as long as they fit the grooves and have the proper end clearance.
Making rings is or can be tricky. They are usually cast iron and you have to figure the oversize you need to get the ring tension in the bore. There may be a formula for figuring it all out.
Just buy the rings from Hastins and be done with it.
EDIT: My book is old and gives the HH60 as Bore 2.625-2.626"---Piston dia. 2.6210-2.6215"---Ring end gap .010-.020".
I think you better measure the bore again, I don't think the cylinder wall is thick enough to have that much wear, at 2.801" the piston would flop around in the bore. If it's that bad it's a throwaway now.
03-02-2009, 03:51 PM #3
Soichiro Honda got started making piston rings in his home shop. Somewhere in the world's libraries is the whole story, but a humorous anecdote: He submitted a set of piston rings for testing in a factory and every one of them broke. Ashamed, we went home and perfected them.
I had a friend nearly 40 years ago who made them from cast iron. He machined them from pipe, ground them to size, heat treated them. The last operation was to split them, set the ring gap, and finish the ends.
It was quite an operation, but rings were not available for what he was working with.
03-02-2009, 03:55 PM #4
My dad told me a story of my grandad turning a set of rings for him out of an old cast-iron flat-iron. Gran wasn't very pleased when she went to use it
03-02-2009, 03:55 PM #5
Maybe worn too much for a bore?
Measure cylinder "ridge" this should be original bore size.
03-02-2009, 04:09 PM #6
among model engine makers making rings is SOP. Cast iron is the material of choice. The trick is to make them a little bigger than required, then break them, then turn the final od while its slightly compressed in a fixture the other approach is the expand them on a mandrel and heat treat so want to stay expanded, either way creates the outward force on the wall. There's a bunch of web content on this if you really make your own rings
03-02-2009, 04:39 PM #7
03-02-2009, 05:27 PM #8
Cast iron? Ductile iron I thought
03-02-2009, 06:06 PM #9
Search "George Trimble piston ring" in Google. His is arguable "THE" method* for making rings for model engines. George published his method in a series in Strictly IC magazine. The magazine is no longer published, but the back issues are available (http://www.strictlyic.com). Unfortunately, by the time you bought raw stock for the rings and fixtures, plus the articles, you'd be miles ahead buying the rings commercially.
Rody, most rings are cast gray iron, not ductile, as the latter won't give a clean break when snapped to form the gap.
*Pounds of ink have been spent arguing the point. I've made rings using the Trimble method and they worked great.
03-02-2009, 07:49 PM #10
Why do you break them instead of cutting a piece out for the gap? Don't you file fit the end gap anyway?
03-02-2009, 08:29 PM #11
Machine slightly oversize, notch for pin, break, cross ends to spring inward to reduce diameter, slip ring into bore to see what needs to be removed by a file to let them pass each other for alignment, plus a few thousandths for expansion, working with thickness gauges. Insure that the semi circular reliefs in the ends will still clear the pin.