why did it break?

[Quickshoe]

I had the opportunity to assist in the teardown and inspection of my old motor. 12A. It failed during its' 5th season. 3 years for me, 2 years for its' current owner.

Other than the obvious "rebuild after 4 seasons" what could have been done differently?

The front rotor broke an apex seal in half. The rear rotor broke a rotor at the apex seal groove. One of the rotor housings had a crack about 1/2" long from the leading sparkplug hole.

Is this a result of detonation? Was their too much clearance between the apex seal and its' groove? Insufficeint oil in the fuel? Too many rpms? What?

[ddewhurst]

Quickshoe, could a potential contributor to the issue be broken seal/carbon chunks/partial lockup ??

Have you talked with any Pro motor builders about this failure ?

Have Fun http://Forums.ImprovedTouring.com/it/wink.gif

David

[Tak]

Severe detonation will usually leave metalic deposits on the spark plugs (it can acutally plate them with aluminum/iron/chrome).
Overheating will melt the sealing rubbers by the combustion chambers.
Broken apex seals without either of the above indications sounds like big time over rev. Is there evidence of the rotor faces hitting the housing (look for scuff/scrape marks between rotor indentation and apex seal groove)? This is also an indication of excessive RPM's.
Did the oil smell funny, or any other oddities?

[Quickshoe]

David,

The rotor and eccentric shaft bearings look good. There is a deep grove in one of the rotor housings (caused by the broken apex seal) Haven't spoke with any pro builders about it yet.

Tak,

Oddities? The OIL wreaked! The coolant passages in the rotor housings were a very light tan and had formed a very thin paper-like skin.

All the "rubber" seals looked good, the apex seal springs seem to have lost most of their height/tension. All the side seals looked good, the gears and side housing were in excellent shape too!

When I first put this motor together I took great care in making sure everything was clean and within tolerances. However, if a wear component was still within the first 50% of it's life, it was re-used. All gaskets, seals and and springs were new. I was advised that it was "prefered" to use the old bearings, even though there was copper visible. The bearings look as good (bad) as they did 5 years ago.

This failure doesn't appear to be caused by overheating. The driver came off the track saying he was way down on power and it wouldn't rev. It sounded as if one ignitor had gone south. We verified that all plugs were firing. We then pulled all the plugs and cranked it over, no stuff came puking out of the holes. A finger over each spark plug hole while cranking verified he was done for the weekend.

[moto62]

Originally posted by Quickshoe:
The front rotor broke an apex seal in half. The rear rotor broke a rotor at the apex seal groove. One of the rotor housings had a crack about 1/2" long from the leading sparkplug hole.

Is this a result of detonation? Was their too much clearance between the apex seal and its' groove? Insufficeint oil in the fuel? Too many rpms? What?


[/B]You guessed right on everything. Five years on a race engine is probably equivalent to maybe twenty years on a street car.(No calculated formula here, just an educated guess). So I wuold say you did a great job rebuilding that engine. To ans your quests.- The cracks around the plug holes are normal but usually happens around the trailing plug(upper)hole. This is a high stress & heat area. Did you use new rotor housings on the rebuild? Check the apex seal groove in the rotors if they are Vee'd out. After five seasons the apex seals heights are probably in the 6.5 to 7mm range. this will cause them to flop back and forth tremendously eventually causing them to shatter at high rpm. A lot of this stress and wear usually is a sign of detonation. Knock back your timing about two degrees (may not be at optimum advance but long will live your next engine) http://Forums.ImprovedTouring.com/it/smile.gif
Ray
[email protected]

[Quickshoe]

Thanks for the responses.

Yes, the apex seal grooves are "v"'d out. Some more so than others. I am sure they are manufactured with parallel facings. As we go searching through the spare rotor collection we will look for the matched set (same weight) with the least amount of "v". Is anyone aware of a wear limit on this?

If the largest difference is .001" across the top vs. at the bottom, and that's too much, I will advise to trash the prized rotor collection. Yes, rotors cost money, but nothing bothers me more than mechanical problems at the track. All the money and time invested in a weekend, and I have to go home because I tried to save a buck?!?! No thanks...maybe the current owner will feel the same way. Standing on the sidelines watching a race sure does suck!

[moto62]

[quote]Originally posted by Quickshoe:
[B]Thanks for the responses.

Yes, the apex seal grooves are "v"'d out. Some more so than others. I am sure they are manufactured with parallel facings. As we go searching through the spare rotor collection we will look for the matched set (same weight) with the least amount of "v". Is anyone aware of a wear limit on this?

Quickshoe. Funny you should ask this. There is no mention of a wear limit on this. According to the Mazda comp tech tips, it just says to look at the rotor groove from the side (profile view), check for v-shape at the top of the groove. This is a sign of excessive seal drag. Your guess is as good as mine. However,if you are able to notice any type of wear in the grooves, chuck it. See the comp parts catalogue tech tips for the possible causes of seal drag.
Ray
moto62

[Tak]

Stinky oil makes it sound like the oil overheated. That could kill apex seal springs, causing the seals to slap around...I dunno, kind of grabbing at straws here! Worth a look to see if something is blocking the oil cooler. Was the oil metering pump working and/or do you run premix (I use both)?
Tak

[Quickshoe]

Premix only. Have always used this method. Didn't trust the metering pump.

The oil in the gasoline is responsible for lubricating the apex seals, apex seal springs and the side seals and their springs. The engine oil lubricates all the bearings and the eccentric shaft. Everything within the oil seals on the side of the rotors, correct?

Perhaps you've nailed it! The amount of oil in the gas was inadequate. Causing the failure of the apex seal springs, leading to the apex seal and groove issues.



[This message has been edited by Quickshoe (edited December 02, 2002).]

[Tak]

Quickshoe-
The more I think about your post, the more I think the stinky oil inidicates your cause of failure (overheating). My concern was about overheating the engine oil. You are correct that the oil in the fuel lubricates all the sliding seals, but the engine oil is critical for keeping the rotors cool. If the rotors get too hot, the apex seal springs lose tension and the apex seals bounce, then break. Keep in mind that seriously overheated oil will continue to lubricate up until the point that it cokes (starts to char and leave black carbon ash ~over 600 degrees). To the best of my knowledge, oil starts to go stinky in the 300-400 degree range. I would be VERY concerned to see 300 degree oil temps in a rotary!!
Anyway, enough rambling. Are you going to build the next motor?

Tachi Callas
#29 ITA SFR

[Quickshoe]

Tak,

I might assist in the final assembly. This is the main reason I was asking the questions in the first place. I wanted to make sure I didn't make the same mistake(s) twice.

The motors really are remarkably simple to rebuild. I don't know why more people don't do their own.

I won't be doing my own FF motor though. I want to make certain that it's 100% legal. I don't want a mistake on my part to get me DQ'd or labelled a cheater.