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Index > Engine/Drivetrain > Thread: Dead engine? Or Not?
Thread: Dead engine? Or Not?

Posts: 319
posted February 21, 2006 08:47 PM

Dead engine? Or Not?

Hey Guys,

Long time, no post. Oh well. Here goes.

I just aquired a 74 from a friend that said he parked it with carb problems. I went thru the carb today, evidently my friend had botched his attempt at a rebuild and added one to many balls under the injection nozzels from the accelerator pump. It wasn't pumping to say the least. I didn't do a complete rebuild from scratch, but all the circuts blew clean and the overall apperance didn't appear bad. I screwed it back together and fired it up.
ONE LUNG....OH NO!!!!!!!!
Now all that leads me to this.
I realize that listening for 6 disinct pulses spitting out of the lower spark plug holes is by no way accuate in testing compression, but I have seen this method applied with success in the past. And that appears to be the case here. 6 distinct spits. I even seperated them and listed for 3 per side and they are there, but the back of the motor is dead.
The venturies are drawing gas down evenly on both sides of the carb. There is not blow back from venturie 2, like copressiong blowing back up.

From the shade tree book of Rotary mechanics.

3 spits per side= good
2 spits per side= side seal
1 spit per side+ apex seal

I did a basic check of ignition, it appears to be functioning properly. I haven't put a light on the timing yet.

Any body got any ideas??

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Posts: 356
posted February 22, 2006 06:35 AM


Jeff, put a compression gauge on the rear rotor, find out just how much compression its building. Try using some marvel mystery oil down the carb. Rotaries like to fire with some oil. Maybe the Apex seals are just stuck and the centrifical force of running will help bring them back. If you need a rebuild let me know I can build you a 4 port using 12A sides and 13B rotors and housings, if we can find some good ones. Sea Foam also helps break up carbon if you want to pour some down the carb.

Good luck and let us know how it goes, Charles
74 REPU "Red"
74 REPU "Jethro" "TII"
74 RE-Courier vert
79 SA-SE(aka deathtrap)
79 SA-SE-FC (project
TN Forum:

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Posts: 319
posted February 22, 2006 12:45 PM

yes, good idea

Hey Charles,

I was gonna pour ATF in the rear housing, but Marvel oil would probably be more caustic. I'll let it soak for a day or two.
Gonna run by a friends house this week and pic up his Compression tester for the final verdict.

I am not sure what I'll do if the motor is toast. I haven't thought about an engine build in a long time. I do have the option of the motor out of my 77. Its in the process of a frame off right now. The bed is off, completed, and ready for paint. So its time to jerk the cab off anyway. I was hoping to lift the cab up and over the motor, sorta wanted to take a few pics with the engine/tranny mounted to the frame before removing it. Better speed up the restoration if I want that picture.
That still leaves me with an empty engine bay.

I'm gonna let it soak and try again to start the 74 in a couple of days.

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Posts: 1877
posted February 22, 2006 01:01 PM
Edited By: klaus42 on 22 Feb 2006 13:06


...*may* un-stick a seal, but it will not remove carbon the way AmsOil Power Foam will. If you really want to clean the motor out, well... you may wish to have a can on hand for as soon as you can get her running. If you've never tried it, you will be pleasantly surprised... after the black pollution clears... and you drive the piss out of it, immediately, for 50 or more miles without shutting it off. :)
The accelerator pump's operation should also be immaterial to the basic running of the engine.
--I've had less-than-obvious blockage/crud impedimants in the carb. inlet, etc., act very much like failing ignition on one rotor...(!)
*What about the possibility of a vacuum leak?* That might account for your syptoms...
Also, you can guage what's basically going on compression-wise by pulling a plug, and turning over the motor by hand, and feeling/observing what comes out: (how many/ how strong pulses). A friend and shop towels are handy...
I'd try verifying *everything* about proper ignition, timing, and fuel delivery particulars statically; clean the plugs, scrape the contacts in cap and rotor, etc... then, pull/push start down the road, in the time-tested method.

Best wishes for your 'rotary revival'!

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Posts: 319
posted February 22, 2006 02:20 PM


The accelerator pump injection nozzels were what the last owner managed to put together wrong. He couldn't get it to restart after he tore into the carb. I think there is a possibility what he mistakingly thought was a bad carb may have been a bad motor?
Where do you buy the Amsoil foam?
You think the ignition could be out enough that one rotor could still fire well enough to keep the engine alive?

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Revvin Up
Posts: 53
posted February 22, 2006 06:41 PM


Another possiblity, (not good) is that your engine has been run out of oil and spun a rotor bearing. They usually only get one and it's usually the rear. You might try getting it started on the one rotor and check the oil pressure. If it isn't the normal 68 PSI that could be the problem. Otherwise, if you have it running and have fuel and spark to the "dead" rotor, it should run. It would be unusual for the apex seals to be stuck on just one rotor so tight it won't loosen up pretty quick unless it has been overheated and got water in the housing due to the crushed rotor housing and burnt water seals, or the spun bearing I suggested above. To check the compression get a standard piston compression gage and take the schrader valve out of the hose that is typically used as a check valve. Then you can just watch the dial as someone cranks the engine and watch for where the needle bounces to. A "good" engine should pop about 115 psi for each compression cycle. If you have any less that 60 PSI they will probably not fire at cranking speeds.

Happy Rotoring,

'77 RPU
'75 RPU (V-6)
'76 Courier
Rotary Sprite (3 - 2 project)
'85 IT 7
EP '85 Rx7 (in progress)
'85 GSLSE (4)
C6 Corvette Roadster

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Posts: 1877
posted February 23, 2006 09:22 AM

Many 'possibilities'...

What the previous owner managed to repair properly, or (inadvertently?) mess up along the way, only you will be able to determine from careful investigation... (nevermind the 'original' 'issue'.)

AmsOil Power Foam is available through any AmsOil 'dealer', as well as direct from the company, and should also be obtainable (even if you need to order it) from any retail chain that has any AmsOil product on their shelves. Racing Beat at least used to feature their products for many, many years... and tested and proved their worthiness in winning rotary race applications.
Factory Direct 7 am to 5 pm Central Time, M-F, 1-800-956-5695 ...AmsOil Inc., 2206 Winter Street, Superior, WI., 54880. Best results with Power Foam used on a freshly-tuned engine; spray into warmed-up, running motor's intake, filling the carb with the entire can's contents after it chokes the motor... don your respirator, and fire her u[p as soon as it dissipates... keep her running, and immediately go for a nice drive, at least 50 miles, preferably more... get your foot in it through the gears--really blow it out after being cautious initially--your engine will keep running better and better for perhaps the next 500 miles, even! Their 'Performance Improver'added to the gas tank also gives great results used in combination with the Power Foam--.

Anything's possible, regarding what may or may not be going on with your motor... until you positively eliminate certain potential issues... or locate the cause(s).

Sometimes, symptoms are deceptive as to the cause...

Process of elimination. Best of success! :)

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Posts: 319
posted February 23, 2006 12:20 PM


I am supposed to pick up the compression tester this monday and eliminate the first obvious problem of a dead rotor.

I'll check the oil pressure next.

I cant help but wonder if the previous owner dropped something like a check ball, copper washer, cotter pin, anything down the carb while he was fiddling with it? I guess thats just speculation.

I have a piston tester, let me see if the mod will work on it and see how close it is to the rotary tester.


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Posts: 319
posted February 27, 2006 08:29 PM

ton of bricks

I walked past the truck yesterday afternoon and it hit me. The brake booster.. I had a truck about 10 years ago that had the same problem when I bought it.
Motor runs great when plugged off from the booster.
Does anyone know of a place that is rebuilding brake boosters??
77' REPU plus a few spare parts
for it.
85' GSL-SE
83' GSL

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Posts: 1877
posted February 28, 2006 09:48 AM

Aha! Damn vacuum leak...

Congrat's on your inspired diagnosis! I think Brad was the last guy here to look into brake booster rebuilds; he may have the info. you desire--. :)

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Posts: 319
posted February 28, 2006 11:58 AM

the gauge never lies

I have a lead on a brake shop here local that can do the booster. But last time I had one done, about 10 years ago, the guy said they were going out of buiseness.
I think it is the same shop?
But, any other lead is appreciated.

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