1st Generation Specific (1979-1985) 1979-1985 Discussion including performance modifications and technical support sections

Is my 12a dead?

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Old May 6, 2008 | 06:14 PM
  #26  
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I will try that doc,

Not tonight though.. the neighbours are having a barbecue and I had soaked the inside of the engine in seafoam..
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Old May 6, 2008 | 11:28 PM
  #27  
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Soak that sucker Mr. Melon, at least the down time will do some good. If it's any consolation, my White One finally recovered from it's "bad apex seal" today, it has never run better!

Like Doc says, you need to know about the spark and compression. Kind of like going in for a colinoscopy, but you'll be glad you did it once you've got the data.
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Old May 7, 2008 | 02:50 AM
  #28  
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Originally Posted by yetterben
um if his trailing was dead he would have no tach and no fuel pump!
Exactly.

To the OP: what the doctor says. Get numbers on compression, esp. rear rotor. And get an actual timing light and check timing. My money would be on low compression but I've also seen out of whack timing make the car have the symptoms shown in the videos.
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Old May 7, 2008 | 10:44 AM
  #29  
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crap I keep forgetting my car is wried differently. good luck finding the problem melon
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Old May 7, 2008 | 02:25 PM
  #30  
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Originally Posted by swbtm
crap I keep forgetting my car is wried differently. good luck finding the problem melon
You mean different than stock or different than an '85?
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Old May 7, 2008 | 05:14 PM
  #31  
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UPDATE!

Hey guys
I got my hands on a compression tester and it says it all, front rotor is all good and equal.. and the rear rotor is 1 good 2 bad... why is it always the rear rotor!

I guess I have a messed up apex seal.

I was just hoping to do everything I could to avoid accepting the fate, but now I guess its new engine time.

The car is still in running driving condition, would it damage anything if I just kept driving it? is that a bad idea?
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Old May 7, 2008 | 11:14 PM
  #32  
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Not really. I drove mine for weeks in that condition until my new engine was ready. Good luck and see it as a chance to drop in a quick *** engine!
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Old May 7, 2008 | 11:17 PM
  #33  
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Thats why I wanna buy a ported engine now so when the stock engine blows I can just swap em......... Good luck with the car rotarymelon!
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Old May 7, 2008 | 11:18 PM
  #34  
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Yes, finally I have a reason to do a full cleaning of the engine bay

Thanks everyone
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Old May 8, 2008 | 08:36 AM
  #35  
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Nice work Mr. Melon, at least you know what needs to be done now and as you say, it will be a good opportunity for a little upgrading and housecleaning. Have fun and let us know how it goes.

Ray
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Old May 8, 2008 | 11:30 AM
  #36  
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crad, I have an electric fuel pump that I think is wired up separately. So, this is different from stock.
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Old May 12, 2008 | 05:42 PM
  #37  
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**Updated!

Today I decided to pull off the header and check the apex seals for myself.

Off with the header, i turn the engine by hand, feeling around in the rear exhaust port, (mind you, this is not a good idea, do this very slow! I nearly took the end of my finger off with a rotor ouch!)

anyways, I felt 2 good springy apex seals.. then the 3rd one.. I couldnt tell what I was feeling exactly.. either a slot where the apex seal should be.. or a very stuck rigid seal.. I cant imagine the apex seal could have shot itself out of the exhaust?! I know anything is possible.. but my car runs and drives still!

I figure I will pull the engine anyways.. and if its just stuck, I will loosen er up and away I go.. option 2 will have to be a new engine, because im sure an apex seal leaving the rotor would destroy the housing.

I tried to get my camera in there, but i only got pics of the exhaust port, and could never see the rotor itself.

my compression on the rear rotor appeared to be 60-60-30.. pretty terrible
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Old May 12, 2008 | 05:47 PM
  #38  
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apex seals get shot out the exhaust all the time. its cool when its straight pipe back to pass threw can. WATCH OUT SHRAPNEL!
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Old May 12, 2008 | 06:03 PM
  #39  
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When I lost my apex seal, the engine seemed like it would shake itself apart at idle. And the power loss was extreme. I just barely made it home. If you are still able to drive around, I have to doubt that you really lost an apex seal...
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Old May 12, 2008 | 06:23 PM
  #40  
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I actually considered driving it.. the idle sounds kinda cool.. like a bridgey
lol.. the power loss is only noticeable when starting from a stop.. when your going it accelerates nearly as well..

think it might just be stuck??
I dont know how it could suddnely *stick* itself while driving normally.. i wasnt even pushing it when it happened
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Old May 12, 2008 | 08:13 PM
  #41  
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What kind of sump oil do you use: is it dino or synthetic?

What weight of oil do you use: is it 10w30 or is it heavier?

Do you add MMO or 2-cycle to your gas as a premix?

I'm just speculating, but I'm going to guess that apex seals get stuck because of high ash oil that leaves a lot of carbonish residue that bonds a seal into the mounting groove. The solution is to switch to low ash synthetic oil.

Apex seals probably break from a combination of high ash oil residue hindering their movement and excessive engine rpm that establishes destructive vibration modes that the engine was not designed for. Those destructive vibration modes can be aggravated by oil of too high viscosity that resists shearing and cavitates at high speeds.

Revving the engine high to "blow out the carbon" is a tale that goes back to my fathers teenage years. I don't believe it. Of course, I said the same thing when I was 18.
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Old May 12, 2008 | 09:08 PM
  #42  
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So you don't think reving the engine to remove carbon is true?????? That would suck cause then I have no real excuse to push it to 7 grand..........
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Old May 12, 2008 | 09:28 PM
  #43  
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Originally Posted by risingsunroof82
So you don't think reving the engine to remove carbon is true?????? That would suck cause then I have no real excuse to push it to 7 grand..........
No, I don't believe it.

I have been told this same thing by so many poorly informed people that I suspect it is apocrypha, i.e., rumor. The same kind of people repeat phrases to me that I have heard in commercials, like "the ultimate driving machine", etc.

What would be the mechanism that would remove carbon at high RPM?

What evidence is there that this actually works?
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Old May 13, 2008 | 12:23 AM
  #44  
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The reason people believe this, I think, is because at high RPM it BURNS all the carbon build up out due to the EXTREME heat at the higher rpms.........
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Old May 13, 2008 | 12:53 AM
  #45  
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Originally Posted by bliffle
What kind of sump oil do you use: is it dino or synthetic?

What weight of oil do you use: is it 10w30 or is it heavier?

Do you add MMO or 2-cycle to your gas as a premix?

I'm just speculating, but I'm going to guess that apex seals get stuck because of high ash oil that leaves a lot of carbonish residue that bonds a seal into the mounting groove. The solution is to switch to low ash synthetic oil.

Apex seals probably break from a combination of high ash oil residue hindering their movement and excessive engine rpm that establishes destructive vibration modes that the engine was not designed for. Those destructive vibration modes can be aggravated by oil of too high viscosity that resists shearing and cavitates at high speeds.

Revving the engine high to "blow out the carbon" is a tale that goes back to my fathers teenage years. I don't believe it. Of course, I said the same thing when I was 18.
Right now in the engine is dino 5w30 (i know its a little late for 5w30.. but its from november)

I add 2 cycle to my gas because I removed the OMP



Either the apex seal is gone completely, or stuck.. I did not feel any pieces or partial spring, its just a rigid edge, either the seal itself or the rotor edge, i should be able to tell.. but I cant
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Old May 13, 2008 | 12:58 AM
  #46  
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vacum leak

Check the intake for leaks, Had one that could not get to idle, adjusting the carb did nothing. Rebuilt the carb, nothing, finally checked and found that the intake gasket had blown out at the rear housing. Easy fix. If you got good compression then thats what I'd look for .
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Old May 13, 2008 | 09:59 AM
  #47  
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dude if you read the whole thing you would know he does not have good compression jesus noobs. soak the affected seal with sea foam. get a squirt bottle and soak that sucker!
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Old May 13, 2008 | 12:42 PM
  #48  
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It sounds like a broken apex.Because my gsl broke an apex seal,and is sounded just like that.

Last edited by datsun1200; May 13, 2008 at 12:52 PM.
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Old May 13, 2008 | 12:51 PM
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He already knows it's the apex seal!!!!! Geeze.........
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Old May 13, 2008 | 12:52 PM
  #50  
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From: eau claire
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