Rotary Engine Failure due to Side Rotor/Side Rotor Housing Clearance.. - Page 5

rx4ur7 · 07-07-2009, 03:33 PM

Just saw this thread show on top.

I have been building these things since 72 and have never seen this as a failure point, street or race. The IT motors spent their lives near 8 and the GT motors at 10K.

Resulting damage from bad bearings and or bad build or gear walking, yes, many.

Here are my 2CS.

I do not see the necessity or any cost benefit. Mazda does not include it as one of their build hints, and it is not in my copy of the Mazda RX7 Competition Preparation and Service Manual. I do not have the latest versions though so I will stand corrected if that modification is recommended. (remember I am the factory freak) I do not know of any of the top builders that do.

But I will not dismiss it completely either. Who knows what the future and innovative experimentation may result in. I will leave this one to those with deep pockets. I’m having enough to do with flat bottoming the open road car and working on this buggy.

When a rotary is built properly to spec with new parts or parts that meet spec it will perform and be reliable. It is then to the client to take care of it. A good build isn’t anything if the oil isn’t changed or it is run out of water. (but the light wasn’t on that long, just until it stopped.) They may come in the shop that way, but they leave knowing the proper care and feeding of their investment.

Side seal clearance was not increased drastically. There is no difference between SS and CS. The clearance of SS in the rotor is different because of the design of the new SS.
Rotor to side housing clearances are less .12-.21mm for FD, .05-.19mm for Renesis.

If you are inducing any blow by it will shorten the life of the motor. First by contaminating the oil and building up combustion gases in the oil containment system. Beside loss of power.

***Herblenny*** · 07-08-2009, 02:13 PM

Thank you for your input Rx4ur7!

Quote:

Originally Posted by rx4ur7

Side seal clearance was not increased drastically. There is no difference between SS and CS. The clearance of SS in the rotor is different because of the design of the new SS.
Rotor to side housing clearances are less .12-.21mm for FD, .05-.19mm for Renesis.

That's interesting.. I was looking for that information about FD vs Renesis clearance.. Thanks for posting that.

Quote:

Originally Posted by rx4ur7

If you are inducing any blow by it will shorten the life of the motor. First by contaminating the oil and building up combustion gases in the oil containment system. Beside loss of power.

Same thing was also told by another very experienced builder.

r0t0rhead · 07-07-2009, 08:31 PM

Amen!

***Herblenny*** · 07-21-2009, 08:47 PM

Over the weekend I met up with the guys from SpeedSource and asked them if they clearanced the rotors on their 20Bs.. They said, "yeah we do. But VERY little". I ask how little and they said they barely clearance it..

Also they told me their peak HP is at around 8500RPM.

Just thought I post what I found out

scotty305 · 07-30-2009, 01:32 AM

Interesting thread... I'm no engine builder but I've heard at least a couple of piston guys mention using increased piston-to-cylinder-wall clearances to avoid contact due to the piston expanding when it sees a lot of heat (high boost). Due to the shape of the piston inside the cylinder I don't think those guys would be need to be very concerned with flex or eccentric shaft wobbling... I would venture it's just expansion from heat.

I suspect there are some similarities and some differences between how the piston engines and a rotary engine will react to the additional heat (not a lot of forged aluminum rotors out there), but something along those lines may account for why some builders are suggesting that increased clearances and others don't. I suspect it may be more important in engines that are seeing a lot of heat. This may explain why one builder observed a higher percentage of FD failures than FCs... it's pretty much a given that the FD runs hotter.

Max777 · 10-17-2009, 10:42 PM

All this arguing gave Max a headache.

AnthonyNYC · 10-18-2010, 02:51 AM

I guess I take it for granted but in the NE most of the rotary guys help each other. We share a lot of info and this will only help all of us in the long run.

I take .003 off each face. Some take more off some take less, most I know go with .002. I've run 550-600hp for years with nothing touching. As soon as I started trying to go over 630hp or so, things started flexing and the tips touched and I had the rotors clearanced.

Earlier this year at a drag racing event I spoke with Ray@PFS and asked him one of those top secret questions, not only did he answer me honestly but even offered to send me the part I needed to get it going. In the end we all need to help each other.

Anthony

jamespond24 · 10-23-2010, 10:22 AM

Quote:

Originally Posted by AnthonyNYC

I guess I take it for granted but in the NE most of the rotary guys help each other. We share a lot of info and this will only help all of us in the long run.

I take .003 off each face. Some take more off some take less, most I know go with .002. I've run 550-600hp for years with nothing touching. As soon as I started trying to go over 630hp or so, things started flexing and the tips touched and I had the rotors clearanced.

Earlier this year at a drag racing event I spoke with Ray@PFS and asked him one of those top secret questions, not only did he answer me honestly but even offered to send me the part I needed to get it going. In the end we all need to help each other.

Anthony

I agreed 100%.

Great post I hope we as a community can help each other like this.

07-21-2009, 08:47 PM	#4
*Herblenny* Founder/Administrator/Internet Pitbull :) Join Date: Jan 2008 Posts: 644 Rep Power: 10	Over the weekend I met up with the guys from SpeedSource and asked them if they clearanced the rotors on their 20Bs.. They said, "yeah we do. But VERY little". I ask how little and they said they barely clearance it.. Also they told me their peak HP is at around 8500RPM. Just thought I post what I found out __________________ DGRR 2013 - Year of 13B www.DealsGapRotaryRally.com http://www.facebook.com/Herblenny

10-17-2009, 10:42 PM	#6
Max777 Pirate Join Date: Mar 2008 Location: Central IL Posts: 1,323 Rep Power: 19	All this arguing gave Max a headache. __________________ Rotaries:They are NOT that complicated!

10-18-2010, 02:51 AM	#7
AnthonyNYC Self built and tuned... Join Date: Feb 2009 Location: West Islip, Long Island NY Posts: 14 Rep Power: 0	I guess I take it for granted but in the NE most of the rotary guys help each other. We share a lot of info and this will only help all of us in the long run. I take .003 off each face. Some take more off some take less, most I know go with .002. I've run 550-600hp for years with nothing touching. As soon as I started trying to go over 630hp or so, things started flexing and the tips touched and I had the rotors clearanced. Earlier this year at a drag racing event I spoke with Ray@PFS and asked him one of those top secret questions, not only did he answer me honestly but even offered to send me the part I needed to get it going. In the end we all need to help each other. Anthony Last edited by AnthonyNYC; 10-18-2010 at 02:53 AM.

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07-07-2009, 03:33 PM	#1
rx4ur7 Rotary since 1972 Join Date: Nov 2008 Location: Tucson Posts: 231 Rep Power: 18	Just saw this thread show on top. I have been building these things since 72 and have never seen this as a failure point, street or race. The IT motors spent their lives near 8 and the GT motors at 10K. Resulting damage from bad bearings and or bad build or gear walking, yes, many. Here are my 2CS. I do not see the necessity or any cost benefit. Mazda does not include it as one of their build hints, and it is not in my copy of the Mazda RX7 Competition Preparation and Service Manual. I do not have the latest versions though so I will stand corrected if that modification is recommended. (remember I am the factory freak) I do not know of any of the top builders that do. But I will not dismiss it completely either. Who knows what the future and innovative experimentation may result in. I will leave this one to those with deep pockets. I’m having enough to do with flat bottoming the open road car and working on this buggy. When a rotary is built properly to spec with new parts or parts that meet spec it will perform and be reliable. It is then to the client to take care of it. A good build isn’t anything if the oil isn’t changed or it is run out of water. (but the light wasn’t on that long, just until it stopped.) They may come in the shop that way, but they leave knowing the proper care and feeding of their investment. Side seal clearance was not increased drastically. There is no difference between SS and CS. The clearance of SS in the rotor is different because of the design of the new SS. Rotor to side housing clearances are less .12-.21mm for FD, .05-.19mm for Renesis. If you are inducing any blow by it will shorten the life of the motor. First by contaminating the oil and building up combustion gases in the oil containment system. Beside loss of power.

07-07-2009, 08:31 PM	#3
r0t0rhead Rotary Fanatic Join Date: Jun 2008 Posts: 192 Rep Power: 18	Amen!

07-30-2009, 01:32 AM	#5
scotty305 Rotary Fan in Training Join Date: Mar 2008 Location: Culver City, CA Posts: 84 Rep Power: 18	Interesting thread... I'm no engine builder but I've heard at least a couple of piston guys mention using increased piston-to-cylinder-wall clearances to avoid contact due to the piston expanding when it sees a lot of heat (high boost). Due to the shape of the piston inside the cylinder I don't think those guys would be need to be very concerned with flex or eccentric shaft wobbling... I would venture it's just expansion from heat. I suspect there are some similarities and some differences between how the piston engines and a rotary engine will react to the additional heat (not a lot of forged aluminum rotors out there), but something along those lines may account for why some builders are suggesting that increased clearances and others don't. I suspect it may be more important in engines that are seeing a lot of heat. This may explain why one builder observed a higher percentage of FD failures than FCs... it's pretty much a given that the FD runs hotter.