wvumtnbkr

Well, this past Sunday the rear rotor on our LeMons racer failed. Going into a hard braking zone, the car stumbled and upon corner exit it wouldn't run very well.

Did a compression check, and it came back zero or close to it on all rear rotor faces. The motor sounded bad!

I am looking for "the smoking gun" as to why the motor failed.

The car has all emissions scrapped. It is a 79 12A (presumable original). The carb is one of the modified Nikki carbs. The car is running pre-mix.

On Friday, the car lasted for several sessions of moderately fast driving on a Kart track. Sunday, it lasted about 40-50 laps of hard driving on a "big" track.

The compression was about 85-90 psi on all faces of the engine before the failure.

Water temp was less than 200 F.

Any Ideas? We don't want to put in our other motor and have the same failure!

I have heard during hard cornering and braking that you can get some fuel starvation. Is this true? Would it be enough to "pop" the engine?

How much timing do you have to have before it becomes a hazard?

Thanks!

Rob

p.s. I am a second gen guy myself. I don't necessarily know what to search for on these cars. i did my best on searching, but feel free to point me in the correct direction.

gsl-se addict

iTrader: (3)

Sometimes they just let go for no real reason except for the fact that the apex seals wear too far down. These NA engines will often just keep running until the apex seal height gets well below the minimum height spec. Once it gets so thin, it can no longer be full supported in the groove (or breaks due to weakness) and the seal comes out of the groove and tears up the rotor/housing.

You could tear it down and check the front apex seal heights. That should give you an idea of how worn the engine was.

My old SA did basically the same thing (but was not racing or anything). Taking off from a stoplight in town, lost power all of a sudden, and it started running like crap. At first I thought it may have been an ignition failure, but turned out to be no compression on the rear rotor. Apex seal let loose and torn it up.

wvumtnbkr

I am not sure if we will have time to tear it down before the race. I guess we will have to make time to tear into it!

Thanks!

Any other thoughts are greatly appreciated!

Iceman13

As a note to the original post, compression check on the front rotor after the failure read 78-80psi.

Spark plugs were pulled and replaced about 10 laps before said incident, no signs of lean conditions. Only oddity was that it looked as though something had come into contact with the electrode on all 4 plugs, just a spot where you could see discoloration (apex seal parts?). One plug gap on the leading rear rotor (the one that went bad) was closed way down.

I was also informed that we may have been running the wrong style of plugs. The ones removed were single electrode and protruded deeper into the chamber than the correct style NGKs that we replaced them with.

Kentetsu

Incorrect spark plugs would certainly cause issues like this. You may have chipped all of the apex seals, including the fronts. When you pull the motor out, look in through the exhaust ports and check the condition of the remaining seals.

What plugs were you running? Stick with the NGKs whenever possible. Good luck...


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j_tso

iTrader: (2)

The only warning I had were the rpms dropping a little faster than normal a few days before it went, rear rotor too. I still haven't torn it down yet, but I'd guess like gsl-se_addict said, just worn to where it was too weak and slipped out or broke. It also chewed up the other 2 seals in the process since I had no compression out of it afterwards. My engine was bone stock and didn't premix.

jibco

Hi, I'm on One Point Twenty One Giggawatts!!! too.

Sooooo, we got it back together and I'm sharing some info we got along the way. The plugs that should have never been in there were not nicked by the apex seals. The contact on the ground strap was from the way the casting is in the trailing plug hole. When the motor popped, all signs pointed to lean rear rotor, as seen in the pics below. Please suggest reasons that we'd have such asymmetric ratios. Debris in carb? (Cleaned, no evidence of clogged jet). Huge vacuum leak? (nothing that worrisome, but new intsall is cleaner than before). Run with no air filter? (we did, but I don't see how cramming more air in the rear portion of the intake would not bring with it the appropriate fuel).

We got a WB O2 (LC-1) int he car durring the motor swap. We did a short street run today and saw readings of 10.3 at WOT, so it's rich and we are expecting that. Sterling said it should be rich, but how much? I don't know. The color sort of came in on the rear plugs some after the street run, but not a ton of comfort, IMO.

We'd love to not ruin another 12a if we can avoid it, so ask questions, make blind stabs, share experiences, whatever. We may be just as dumb as we sound.

http://onetonoffun.blogspot.com/
Testing videos
http://vimeo.com/3153233
http://vimeo.com/3153326
http://vimeo.com/3153471

Test day

Popped it, AWESOME!

Evidence that we have some asymmetric A/F issues. Still unsolved.


1st coat of Delorean-ish paint.

Rx7_Nut13B

iTrader: (1)

Hey guys,

Just some helpful info, if you guys have any problems with the motor agian I will have unuff parts to build a few new motors. We are going to have one backup motor.

Just remember that you are more then welcome to hang with us so if need be we can share crap.

We will have a RV, Hottub, generator(s), Welder(s), Dent puller (aka: F-250 diesel w/ chain), lots of rotary parts.

Plus my shop is about 15mins down the road with ANYTHING you would need.

rotarydude

iTrader: (2)

You need to run an airfilter it is an absolute must, just ask Mazda that is what killed their 24 hr rx3 program in 77 and those were new engines.

did you get everything fixed the way you needed to? I would ensure that the carb is mixed really rich, also make sure that the small filter screens in the carb have been pulled out. if you think that you might have some tank debris then run 2 in line filters, I would also make sure that they are in a very very accessible location and you have extras, I would probably bypass the one that is normally down by the fuel pump that way if one does plug it shouldn't be down there where getting to it could be hard.

I am probably telling you a bunch of stuff you already know

Jeezus

iTrader: (4)

I didn't know about the RX3 things. Any more info?

j_tso

iTrader: (2)

That was the '77 Daytona 24h. Both cars ate too much dust and retired pretty early in the race.

Kentetsu

Are you still running with a shutter valve? That came to mind, since it is intended to cut flow to the rear rotor on decelleration.

Also, are you using a stock a stock fuel filter? If so, you might need something that can flow more fuel than that. What I did was split the fuel line, install a stock filter on both lines, then rejoined them before the pump. That way each fuel filter only has to pull half duty...

vipernicus42

iTrader: (4)

What are you using as a fuel pump? what about your fuel pressure regulator? What fuel pressure are you running?

If you've got the stock pump and filter (as Kentetsu mentioned) you might be running into fuel supply issues. As for "why rear rotor and not front", yes the shutter valve might be one, but also remember that the accelerator pump takes fuel from the rear float bowl only, not the front.. So if you're feathering the gas pedal at any point when you're having fuel pressure issues, you'll run dry on the rear rotor first.

I would get one of the 1-10psi gauges from ReSpeed and check your fuel pressure as a start. After that if you're still running a stock pump, replace it with an aftermarket pump and regulator. I've got a Mallory Comp 70 and Holley 1-4psi FPR and I don't have any fuel issues. I've run my Sterling through a year's worth of autocross, and while that's not exactly track racing, at least it's an environment where there'd be some cornering g-forces involved that might be similar (moreso than the street at least).

Since it's a race car, if you don't care about how much noise your fuel pump makes you could go for a cheaper Holley or Carter fuel pump. I chose the Mallory because I needed not only good flow, but also a pump that has good manners since my FB is also my summer DD, as well as my autocross machine.

Good luck. Don't forget to use the right spark plugs

Jon

jibco

We have the carter/holley FPR setup. Sterling told us to run 3.25psi. We played with it up to 4psi with no real change in behavior. Can we run ridiculous pressure with more starve safety and more flood problems?

I don't know what the shutter valve is, I'll have to search around. While working on it, I've seen nothing that would do such a thing.

Anyone care to tell me exactly what plug is preferable here? In the plug thread linked from the faq, i see a lot of BR8xxx. I realize the standard plug type is not applicable here.

Thanks, fellas.

_Nut, we should definitely try to pit near each other. We will be there early Friday.

Anyone have a rotor with intact seals(or just all the apex equipment) I could install in the rear housing of this hurt motor? Maybe get a few hours out of it as a spare? It doesn't look too beat up through the exhaust port.

vipernicus42

iTrader: (4)

On the track I would run NGK BR9EQ-14s, they're rated as the "Highway" plug for stock applications, and should foul less than the BR8s. I wouldn't use any 2nd Gen or Rx8 plugs unless you have a direct-fire ignition system of some sort, which those plugs are made for.

You're pretty much stuck running one of the two stock plugs (either the BR8EQ-14 or the BR9EQ-14) if you have stock ignition, but they're not bad plugs for the task, so they'll do fine. Be careful, the difference between FB and FC plugs is a single letter - "U". The FC plugs all start BUR*EQ not BR*EQ and the guy at partsource has ordered me the wrong plugs on more than one occasion (he owns an FC, and types the "U" in by default, lol)

I wouldn't up the Fuel Pressure past 3.25psi, but I do want to ask which Fuel pressure gauge you're using... I read this article once and it always stuck with me, which is why I have the ReSpeed gauge:

http://www.yawpower.com/fueldel.html

Jon

Iceman13

Shutter valve has been removed and blocked off.

We do have an inline filter before the carter and have already changed it twice due to debris in the tank. The car sat for 2+ years before we got it. Now that we have run at least a full tank through it, the debris is less of a problem.

Would the discoloration in the exhaust port and pipe come from running the motor 1/2 way around the track, up on the trailer, and into the garage with a dead rear rotor, basically washing everything down with fuel?

Fuel pressure gauge is a Marshall 0-15psi gauge.

Kentetsu

Most gauges won't work well at the pressure levels that we run, which is why Billy (Respeed) went through the trouble to find us one that would read accurately at those levels. Well worth the peace of mind, and very reasonably priced. www.re-speed.com

You could try upping the fuel pressure, but if you start losing top end power then you've gone too high.

If I were in your shoes, I'd verify that the jets didn't get clogged by the junk in the gas tank. You can pull the brass plugs near the sight windows, loosen the jets with a screw driver, then use a wooden toothpick to unscrew them the rest of the way and remove them. Saves a little time since you don't have to crack the carb open. Since you are seeing discoloration in the exhaust port, this sounds like more of a constant issue than a part time issue.

If you are still using stock fuel filters, definitely think about my suggestion of running two filters in parralel (not in series) to ensure good flow. I haven't had to change my filters in two years and counting.

Rx7_Nut13B

iTrader: (1)

We will be there early Friday also, I will send you a PM with my Cell..

jibco

Why is this? Doesn't seem intuitive to me. Higher pressure would blow open the inlets earlier, but with fuel use at high rpm, I cant imaging the fuel coming in would affect the jetting.

I don't think the budget allows for a better pressure gauge.

The filters are nice big ones that we can see in.

I inspected the jets and bowls and easy access areas for debris yesterday. I did not remove the jets, as I saw no evidence of foreign matter. Hit it with carb cleaner and closed it back up.

Is there any merit in getting o2 bungs on the individual headers to check A/F on each rotor? Possibly too hot for the sensor that close to the motor... I know if we ARE lean, the heat may destroy the sensor we borrowed.

BeenJaminJames

The discoloration could definitely be from the raw fuel, but the best I could tell it looked like the welds had been slightly melted on the header. Only a complete teardown will tell the cause for sure though. What do the apex seals look like through the exhaust ports?

jibco

2 gone and 1 partial remaining on the rear rotor of the damaged engine. Front looks ok, and both rotors in the good motor seem to have good seals.

Anyone have a source for the flywheel "brake" and the Gigantic 54mm socket on the backside? That is keeping me from opening it up. I've read the factory manual on sequence of tear down.

Kentetsu

Sterling could give more insight into this (and tell me if I've got it screwed up), but from what I understand they are designed to get a bit leaner at the top end. I think it has something to do with holes getting uncovered as the fuel level drops in the float bowls.

What I do know for sure, is that I was running around 4psi, and when I reduced it the top end improved dramatically....

Remember the difference between fuel pressure and fuel volume...

Kentetsu

Last time I pulled a flywheel, I threaded a couple of bolts partway in, leaving a bit sticking out on the face. Then a big iron bar went in between those bolts and wedged against the floor. Hard to describe without pictures...

jibco

How different are we really talking over 1 psi (3-->4) of difference working on those little inlet valves?

I wonder if Mr. Sterling has stumbled across this thread yet...? He seems to be around here quite often and very helpful.

I'd run a volume test if I had that concern, but when we put the empty carb on the new motor and turned on the pump, it filled really quick (like 2 sec to full).

Iceman13

I don't think the welds melted, it looks the same as when I bought it, just a crappy Pacesetter or some other off-brand header.