SuzukiSavage.com - Piston to Cylinder clearance

justin_o_guy2 Serious Thumper Offline What happened? Posts: 55279 East Texas, 1/2 dallas/la.	Re: Piston to Cylinder clearance Reply #15 - 04/29/20 at 07:00:22 I Really Really HOPE that what I now know about rings and ring gaps, I never need again,,And Thanks to all who contributed.. I totally get it! And now I know I wasted HOURS fretting over a biggo Nuthin..
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Armen

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Re: Piston to Cylinder clearance
Reply #16 - 04/29/20 at 12:53:23

Back when I was fettling a buds race bikes, and spent a lot of time the track, I got to talk to a few smart folks.
Next to us once were a guy and his son running a Yamaha 4 cylinder. I asked about ring gaps and squish band clearance. Turns out the dad worked for (owned?) a piston company and had use of the dyno. He says he'd build the motor, run it to 500 RPMs past redline (safety margin) and pull apart. Skim the cylinders and do it over and over til he'd see s faint shiny ring on the perimeter of the piston crown, indicating piston to head contact. Measure things up, and cut the next cylinder to a few thou taller.
Then he'd do ring gaps. Run with tighter and tighter ring gaps until he saw marks on the ends of the rings indicating that the ring ends were starting to to fret. Add a few thou to the clearance and write it all down.
Amazing what you can do with unlimited time and money and equipment and tools and skills.
Closest I ever got to that kind of R+D was doing a few dozen dyno runs in one day trying every combination of timing and jetting.
I've read stories about Irimijari and the development of the 250/6 Honda. Ordering connecting rods in 1mm increments, cams with a few degrees difference in duration, valves in 1/2mm increments, and building a single cylinder test mule of the 250 (so, I guess a 40cc 4 valve motor?) and running every possible combination until he found the best one.
Always in awe of those folks.

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justin_o_guy2 Serious Thumper Offline What happened? Posts: 55279 East Texas, 1/2 dallas/la.	Re: Piston to Cylinder clearance Reply #17 - 04/29/20 at 13:39:58 Yep,, cubic money and time equals performance BUT,, The smarts to know how to determine what works,, mehh, not for sale
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Dennisgb Full Member Offline SuzukiSavage.com Rocks! Posts: 176 Maplewood MN Gender:	Re: Piston to Cylinder clearance Reply #18 - 04/29/20 at 13:48:23 Lots of really good info. You guys are very knowledgeable. I’m on a lot of different motorcycle forums, this one is one of the best. The help and knowledge is appreciated.
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norm92de

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Re: Piston to Cylinder clearance
Reply #19 - 04/29/20 at 14:25:00

Reading all this about piston rings reminds me of the days when I flew Pratt and Whitney R2800 engines.

We had a procedure where we were instructed to not under any circumstances reduce the manifold pressure to less than the RPM, which meant since the RPM was almost always 2500, no less than 25 inches of mercury. We were told by Pratt that if we did we could cause top ring land failure and possible engine failure. Apparently, the top ring can flutter in the groove and cause piston failure.

I was flying with a Captain who one day said I am not supposed to do this and then closed the throttles to comply with an ATC request to descend rapidly.
I was flying that aircraft as Captain shortly after that incident when we scattered R2800 parts over the city of Houston. Anyway a single engine landing back at Hobby followed.

One of the 18 cylinders had disintegrated and it was described by the mechanics as the worst failure they had ever seen. The connecting rod failed after the piston and it took out the complete front row of 9 cylinders.

I don't know why Pratt aero engines would be so critical in this respect. We close the throttle all the time on our bikes.

Seeing that top ring land failure of Mikes reminded me about it. :'(

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Armen Serious Thumper Offline Half-Witted Wrench-Jockey from Jersey Posts: 1452	Re: Piston to Cylinder clearance Reply #20 - 04/30/20 at 06:43:39 Hey Norm, Thanks for sharing that. Great story. Must have been crazy scary when it happened. I looked at some of those motors last year at the Curtiss museum in NY State. Amazingly beautiful. Can't imagine one fragging the way you describe. Wow!
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justin_o_guy2 Serious Thumper Offline What happened? Posts: 55279 East Texas, 1/2 dallas/la.	Re: Piston to Cylinder clearance Reply #21 - 04/30/20 at 06:54:34 Air Force boot camp. Once in a while we would get a free hour. A buddy and I would run over to the museum. I never quite got my fill of staring at those radial engines.
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norm92de Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 1180 El Paso TX Gender:	Re: Piston to Cylinder clearance Reply #22 - 05/01/20 at 11:54:21 Armen, Yes it blew the cylinder/ head right off. It dropped down on to the lower cowling, glad the cowling stayed closed or we would have had a very serious problem indeed. The cooling fins looked like a slinky by the way.
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