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85 Plymouth Conquest Back On The Road!


Tim_C.
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Well, my '85 has been sitting for about 6 years now. I couldn't believe the last registration I put on it was in 2008! It had low compression on one cylinder. It would run and I was starting every once in a while before I tore it apart about 3 years ago. I had hypereutectic pistons in it, stock 7:1 ratio. I boosted up a short hill one time at about 9PSI non-IC, and the spark plug would not come out.

So I removed the pistons with the engine still in the car. LoL! I normally pull it all, but I had no place to put it this time. I put forged Wiseco true 8:1 pistons in it, with the super light pins from Dad. Hastings rings. Had to hone it out by hand to increase the size a little for the forged pistons.

I replaced the cam with a hi-torque/low RPM new grind I had laying around. The grind had been tested, but no one was interested, so I thought I would put it in my 85 Auto car that needs a little low end torque anyway.

So far so good. I have about 300 miles on it. The fuel hose leaked at the crimp near the TB, so I dug out a salvage yard one I had and it is working well. Had a pinhole in the radiator that I was going to pull and have fixed, but it sealed itself. I'll still pull it, but I'll drive it a little more just locally so I can see if everything else is going to hold together reliably first. No reason to doubt anything, but I hate to invest a bunch more if I made a build mistake, etc.. It was the dirtiest build I've ever done, but the pan was clean, and little to no metal in oil. Oil is super clean now, so I'm pretty sure everything is fine.

The car has 94K miles on the rest of the parts, so I thought it was worth saving. It is an ugly eyesore with sun baked paint, cracked up front spoiler, etc.. But the body is straight and rust free. It runs very well for what it is. I still need to tune it up a little with a TPS/ISC reset. I did replace the vac hoses with a silicon set I got free in the Mesquite raffle a few years ago. Thanks SOTTY!

All in all, I have about $550 in pistons, rings and bearings, and I used gaskets I've had laying around, so not much invested there. It cost $174 to re-register it. I'm running ethanol free premium gas in it. I needed to drain the old gas out, but there was still some smell, so I'll run a few tanks from the only pump in town that has ethanol free.

I'm just stoked to be driving this thing again. It had 74K on it when I bought it and rebuilt the engine in it. The OEM build was toast with a cracked head, and water damaged cylinders.

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  • 3 weeks later...

Yeah man - Post a pic I have only seen one with the Plymouth badging EVER. And it was on the Internet.

 

I am very interested in seeing this automobile.

 

Thanks,

 

SLim Jim

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  • 1 month later...
Well, the '85 is back off the road. After about 3K miles, a fight broke out between one cam journal and the cam. Metal from the cam actually moved into the aluminum journal and seized the cam. So the head casting and the cam are junk now. Of course I've got another fresh head to put on it, but that head had bronze guides, and bull hogged valve ports from the valve seat up into the port. Bummer! I even checked to make sure all of the rockers were getting good oil when I first started it. There wasn't any metal in the oil either. Just metal moved from the cam to the journal. Really odd. Checked the shafts and cam caps, and no metal in there, and all passages are wide open. It had to be a temporary starvation/blockage somehow to start the 'meltdown' process, with good oil to it after that being too late. Should just be as simple as replacing the head, but I will be sure to check everything I can, short of pulling the pan. I don't see any need to pull the pan at this point. All of the other journals on the cam and in the head were still perfect too.
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Just metal moved from the cam to the journal. Really odd.

 

I was wondering what that means? Oil starvation seems to be implied.

 

In the first post you said you had to hone it by hand. I have always wondered about the stone/steel material generated by honing. I see a lot of guys saying they honed the cylinders to break the glaze but then I never see mentioned on how the block was cleaned afterwards.

 

The bronze guides, are they the valve guides? Is bronze better than steel?

 

Let's see this eye sore!

Edited by tsi_tom
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The cam made a 'U' shaped groove in it, and the head journal had about the same sized 'U' shaped hump where the groove in the cam is. The cam cap was fine with just a little scarring. All other head and caps are still perfect. I'm leaning toward a bent cam in a straight head, but it is still a mystery. I bagged the crank as well as possible when I honed the walls. Then I sprayed a rag with brake clean and wiped as much as possible by hand. Then I sprayed with pressurized brake clean and wiped until the cloth stayed white when wiping. Like I said, it was still the dirtiest build I've ever done, but I've built engines outside before and never had this problem with them. I'm pretty careful to keep it as clean as I can. When I removed the bags from the crank (honed with crank still in), I sprayed again and wiped, and it was already clean. I'll keep an eye as I tear the head off, but I suspect everything will be fine in the bottom end.
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  • 1 month later...

Well, I found the problem. It is hard to believe, but the head was cracked between the valves on cyl #2. The crack was there before, but we had vacuum tested it to be fine before. We also have a rule that if the crack is seen in the chamber, but does not extend to above the seat, then it is fine as long as it holds a vacuum. Well, the head was fine when I pulled it off the old engine. So I didn't check too close, other than to make sure there was no coolant leaking when I removed it from the old engine. It was a semi-fresh rebuild with more than 26K miles on it, so I didn't doubt the head.

So I just got the head off after the cam bolt breaking as stated in above posts. There were a few drops of coolant on the #2 piston. Not much at all, but some small drops. I almost thought it just seeped out from coolant passages after loosening the head.

What is hard to believe, is the crack went all the way up to the journal. The thickest part of the head has a hairline crack in the cam journal. So very slight amounts of coolant was leaking to finally seize the cam in the journal. Again, the other journals were fine. Only this one near the #2 cylinder that had the coolant leak in the main chamber too.

Anyway, I had about 3K miles on it before it seized, so the head was probably barely sealing for a while until the crack worked its way up to the journal.

I went ahead and put together my new marnal with new Martin Wells stellite hardened valves, newly reground hi-torque mechanical cam for the auto trans car, stock 70 Lb. seat pressure valve springs for the 5500 RPM max engine.

I had a slight fuel leak at the TB gasket, so I went through the TB and cleaned up the intake, etc... There were some exhaust stud issues that surfaced too, so I'm using all new studs in the new AMC marnal head. This is a new head I've had in the box for about 8 years. It is the same type I am running on my heavily modified '87 engine with no problems for many years now (about 27K miles on it).

I've got everything ready to put back together now. Except it snowed heavily and got very cold today, so I finished prepping everything I could in the warm alternator shop.

Been helping my friend Patrick (shop owner) build his 535 HP (computer calculated at flywheel) SBC. We have it in and running with a new 4L60E trans in his '81 Monte Carlo. We are hoping for low 12's at hi-altitude. The computer program he uses to predict power and times, etc.. is quite basic and doesn't work so well for our G54B engine, but it is usually very accurate for the Chevys he builds. Down to the 10th of a second at the track, and sometimes perfectly accurate as to what it says the car should run. It has been about 8 years since we ran the car. For 6 years prior to that, we ran street class with hi 12's and either placed first or second in points each year. Patrick hopes to run it this year, but he probably won't be as devoted to making most of the races like we used to do. We'll see. Its been exciting to get the beast back running again, and encourages me to keep working on my stuff.

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  • 1 month later...
Got the car running again yesterday. New head with new valves and another hi-torque, bottom end power cam. The throttle is much more snappy than it ever was. I didn't have time to take it out for a drive yet. Just broke in the cam, but all looks well so far. I rebuilt the TB and fixed a few other things too. Can't wait to start driving it!
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  • 3 weeks later...
So far so good on the new set-up. Drives very nice with a very responsive snappy throttle even under load. Lots of off boost power. I don't need much throttle at all to drive the speed limit. That's exactly what I hoped for with this auto car. At high altitude, the stock boost level is a few pounds lower, or so PQ said is the reason. Everyone at low altitude says they get 7+ lbs. of boost, but I only get around 4.5 or so on my non-IC cars. I can bring it up easily, but it tends to heat up more up here too. I'd say 7 would be the highest I can go safely non-intercooled.
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  • 2 weeks later...

I'm at about 6,000 feet.

I think I blew the lower downpipe gasket. I heard it blow out soon after it started with the new head, and now a major exhaust noise is there.

Other than that, it is still running great! Very fun in the snow too! It actually does good for rear wheel drive. I have snow tires for it too, but haven't put them on. I'll probably leave them off since winter is almost over. Drove it this morning in a few inches of snow. We had about 2 feet of snow last week and I couldn't get the car up my street. So I did a 180 and put it right back in its parking spot! I could have got up the slight incline if it had the snow tires on it. My one-legged '83 will get up the hill in snow easily too. The '85 posi with snows is a bit better than the '83. The key is to keep narrow tires on them. The narrow tires will drive up most any snow road, one-legged or posi. Wider tires will just sit and spin.

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