Why Apex Seals Break - Page 2 - NoPistons -Mazda Rx7 & Rx8 Rotary Forum
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Rotary Engine Building, Porting & Swaps All you could ever want to know about rebuilding and porting your rotary engine! Discussions also on Water, Alcohol, Etc. Injection

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Old 09-13-2017, 04:48 AM   #11
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Default Re: Why Apex Seals Break

Originally Posted by Barry Bordes View Post
Thanks Lynn for your attention to this thread.
I guess this SAE paper 741091, may be interesting for someone:

The Effect of Selected Coolants on Metal Temperatures in a Rotary Engine
1974-02-01 Technical Paper 741091 G. A. Paul

Rotary engines, by design, are somewhat more difficult to cool than conventional reciprocating powerplants. This arises in apart from the fact that all four cycles do not take place within the same physical portion of the engine. The basic aim of this research was to study the metal temperatures of many points in the rotary engine with standard and experimental coolants in an attempt to develop a product with superior heat rejection properties in a conventional cooling system. The engine used for the experiment was a two-rotor liquid-cooled Wankel engine obtained from a 1972 Mazda R-100. Both road and chassis dynamometer evaluations were run over a wide range of operating conditions to obtain a comprehensive look at coolant performance. The parameters studied for each coolant were road speed, engine load, coolant concentration, and ambient temperature; the coolants tested were ethylene glycol, water, and the experimental coolants XA-1318L and XA-1318.1L.

Altough Dow seems no longer producing these coolants, based in the non-toxic propylene glycol, there's something very close, made for cooling systems of Solar Energy installations: 'Solar57', sold by Pequinsa, in Navarra, Spain www.quimica-pequinsa.com

Also SAE paper 740159: A Rotary Engine Test to Evaluate Lubricants for Control of Rotor Deposits 1974-02-01 Technical Paper 740159
J. J. Rodgers, N. E. Gallopoulos

During development of the General Motors Rotary Engine, the lubricant was recognized as important to its success because certain lubricants produced deposits which tended to stick both side and apex seals. Consequently, it was decided to develop a rotary engine-dynamometer test, using a Mazda engine, which could be used for lubricant evaluation. In an investigation using an SE engine oil with which there was rotary engine experience, engine operating variables and engine modifications were studied until the greatest amount of deposits were obtained in 100 h of testing. The most significant engine modifications were: omission of inner side seals, plugging of half the rotor bearing holes, pinning of oil seals, grinding of end and intermediate housings, and using a separate oil reservoir for the metering pump. Using this 100 h test procedure, three engine oils and five automatic transmission fluids were evaluated.

I attach an sketch about the places of holes inyecting air, in the Exhaust Port region of side plates, for a better performance, less emissions, better fuel economy, from Mazda research in the book by JP Norbye; as gasolines now are unleaded, and the oils that don't leave ashes and gums are known, situation is better, the other image is from a SAE paper 720466, by Yanmar Diesel.

A higher rotor surface and housing temperature, as in the GM Iron housing Wankel, helps fuel economy, as it reduces the quenching effect from cooler sides of working chamber, but above 130-140 C of working housing surface temperature, oil carbonizes, and lubrication is lost, perhaps some S2Mo additive, as in the Mazda 24 h de Le Mans winner car, may help (eg LyquiMoly, 1 cc per liter of oil in gasoline mix). Regards. Salut +

There is evidence of badly overheated spark plugs. The tubular column of aluminum that forms the spark plug hole complex in the housing has grown longer due to the heat. And yes this does deform the housing wall and raises it around the plug hole. After a long period of this complaint, there will be radial cracks around the leading plug hole, and usually a single horizontal crack through the trailing plug hole.

It would be a miracle if this engine was not detonating at high boost. So let us just cut to the chase, and say it was detonating, and then we must think that the Lambda sensor has reported to the controller that there is a problem and the controller has pulled out as much spark lead as it can and that apperarently is not enough to stop the problem. The gas leaks across the plugs are overheating the next charge and making another detonation event a sure thing.

The detonation events take place next to the apex seals next to the damage you have noted. The stock apex seals are really very strong and normally survive higher boost than you say these have been exposed to. Racing Beat and others offer a machining operation that cuts grooves around the spark plug bosses to increase the removal of heat into the coolant (more surface area).

I think the swelling of the spark plug boss is an inherent problem with the rotary design and the one we may be able to correct or at least minimize it.

One thought, as shown in the above images, would be to sever the fins on the boss. This would still cool the plug boss but would allow the horizontally adjacent surfaces more heat. This might change the topographic like temperature hill to more of a step

Barry Bordes
Attached Thumbnails
Why Apex Seals Break-mazda-exhaust-port-air-injection-points-j-p-norbye-wankel-eng-p-342.jpg   Why Apex Seals Break-charge-cooled-rotor-shell-rotella-30-vs-shell-x-100-sae-paper-720466-yanmar-diesel.jpg  

Last edited by urquiola; 09-13-2017 at 04:56 AM.
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Old 10-03-2017, 08:14 AM   #12
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Join Date: Jul 2008
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Default Re: Why Apex Seals Break

The modifications made to the coolant jacket have been made on the Renesis Engine for the RX8. Just thought I would add that carrot of info.
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