Rebuilding engine- Need advice (and to vent)

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73SwingerBuild

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Hi all.

This isn't A-body specific, but it is Mopar. I have a 1972 Roadrunner and I'm looking for some advice on a rebuild. And I could use to vent.

My Dad and I restored the car when I was younger and it's been on the road about 8 years now. It has a 400c.i. HP motor, fairly stock, 0.030 over with a stock cam, stock dual plane intake, mildly ported stock heads, and stock cast iron exhaust manifolds. It's pretty much restored to factory specs but performs very well.

Anyways, I had it out about 3 years ago and it started to overheat a bit when I threw the water pump belt on the highway. I noticed it shortly after but the temperature gauge was almost pegged. Nothing blew in terms of water jacket plugs or cooling system components, but the radiator cap did open up and purge the excess pressure/coolant through the overflow drain hose.

Since then, I've been noticing more and more issues. Not huge issues that make a rebuild necessary, but a lot of small issues that make one seem imminent. Examples:

1. There are definitely some issues with the carb. It's a stock Carter TQ that's been rebuilt a few times and I'm starting to think there's either a vacuum leak or perhaps I just don't know enough about them to keep it tuned properly. It runs fine at speed, but just won't stay idling.

2. Power steering box developed a leak at some point. This could be resolved by removing the box with the engine still in the car, but I believe most of the driver's side exhaust, steering, and the torsion bar needs to be removed to access it.

3. There was a small water leak down the passenger side of the block. I still haven't pinpointed where it is coming from, but it started occurring after the engine overheated on the highway. It seems to have subsided for the the past year or two, but sometimes it happens after a short drive around town.

4. The exhaust manifolds have both developed small leaks around where the flange meets the head. They both also leak where they connect to the exhaust, but this may just be due to the crappy head pipes that my Dad had the local exhaust shop put on the car. I repaired the driver's side exhaust manifold leak by putting a new gasket on, but the threads on the exhaust studs were terrible and I could only tighten it so much before I feared they may strip.

Moving forward, I feel like a good rebuild of the top end of the motor would help to eliminate any and all of these issues. I could also take the time to upgrade to a slightly more aggressive cam, possibly a new Street Demon carb (the new one that looks like the TQ reinvented), and possibly some TTI headers. I would be keeping all of the stock equipment obviously, but I really want to make the car more fun to drive without taking away from the value of the car (it's all numbers matching).

In addition to venting my thoughts, I'd also like opinions on whether i'd be better off leaving the motor in the car and removing all of the top end down to the deck, or if I should just pull the entire motor out and rebuild it on the engine stand. I hate working over fenders, but I know pulling the engine out involves pulling the transmission, radiator, and all of the plumbing associated with the transmission and HVAC system, all of which are perfect right where they are.

Thank you all for letting me vent. Any responses and opinions would be very welcome. I'm just losing patience with the car but I would rather keep it than sell it.

-Mike
 

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Have you done a compression check on each cylinder to see if you may have blown a head gasket? Do you have any coolant in your oil?
 
I think my decision would be based on whether the entire engine needs to be freshened up in the looks department. If the block looks shabby then I would pull it,'repaint the block while tending to the upper end issues, change those manifold studs, look for the mystery leak, and also have full access to the steering box issue. I also don't relish the idea of doing all that work over the fenders, especially the steering box issue!! JMO of course, but a car that nice needs to be treated as such!! Good luck with the project, Geof
 
Pauly,
I haven't done a compression leakdown test, but there's no coolant in the oil, no smoke from the exhaust, and it runs awesome at speed. It just won't idle. I thinking carb or vacuum leak. But perhaps a leakdown test wouldn't be a bad idea.

Geof,
Thanks for the input and compliment. I definitely want to keep her up and running.
The engine is in pretty good shape cosmetically. Hardly any grime at all.
I can definitely access everything working over the fenders... Just not sure if it's worth straining my back and possibly damaging the fenders. Those B-body fenders are HUGE compared to the A-bodies lol.
 
Wow, That is a very VERY nice Roadrunner, I would be under the car removing the dust
shield and T.converter bolts, and strap the trans up to stay in place, remove the starter, radiator, fuel lines and carb and pull that numbers matching engine and get it on a stand I believe.. That is a superior car and well worth a new carb or have it rebuilt by a pro, Thats what my planes would be on that great 72 RR. I could do the engine but the carb would have to be dun by some one ells... Nizzze RR.
 
That is a SWEET numbers matching big block Road Runner!
I definately wouldn't sell it.....
I agree with Geof and would pull the motor.
 
Thank you all for the compliments. It sounds like pulling the motor is the best way to do it all right.

From a value point of view, would it detract from the car's value if I put one of the Street Demon 1904 carbs on it (http://www.summitracing.com/parts/dem-1904/overview/)? Rebuilding the original carb was quoted ~$250 by a member here who seems to be the Thermoquad Guru. However, that still uses the original emissions-based carburetor with the original fuel bowl, which is prone to cracking/leaking. For $150 more, I could get the all new carb which I have been reading some good reviews on. Also, I think a car that starts up and drives reliably holds more value than one that doesn't. But I'm not sure where to go with this one.

I also have a terrible belt squeal that I can't seem to get rid of... The car has four belts to run the alternator, powersteering, waterpump, and A/C. I was thinking of getting one of those serpentine belt conversion kits, but I feel like this actually will detract from the value of the car. They also only come in chrome, and I don't like too much chrome on a factory engine. Just my personal feelings.
 
I would also like to add that 1972 was a strike shortened production year and that your Roadrunner is a pretty rare bird. I would highly consider keeping this car above selling it, as
It is not only pretty rare, but with the driveline described I doubt it could ever be replaced!!

It's a keeper, and definetly worthy of all the attention afforded to it!! Geof
 
I would also like to add that 1972 was a strike shortened production year and that your Roadrunner is a pretty rare bird. I would highly consider keeping this car above selling it, as
It is not only pretty rare, but with the driveline described I doubt it could ever be replaced!!

It's a keeper, and definetly worthy of all the attention afforded to it!! Geof

Good to know! lol

I think I just needed to vent my frustrations. I plan to pull the insurance on it soon and yank the motor. It won't cost much to put new gaskets on everything. I think the only expensive item will be the new carb and new head pipes. But i think it will be worth it in the end.

Thanks all! And feel free to chime in about the value of the original carb.

-Mike
 
To find out which belt (or component) is squealing, pull one belt at a time. When it stops, you'll know. That new Demon carb looks great, but check the cfm. I thought they were only 625 cfm which may be a lot smaller than your TQ. Some of those were 800 cfm.
 
Things like a carb change and such are easily changed back,'and couldn't possibly hurt the value!! You're not selling so its a non issue. Do what makes the most sense for your drivability, and like you mentioned above box up the original carb for safe keeping!!

Unless you're entering it in concours judged class, bolt on changes to increase performance are A-OK!! Or, you can just trade it to me for my GTX and ill take the heat from the concours crowd!! Just a thought!!!LOL!! Geof
 
I'm not quite on board with yanking the engine, but here are my thoughts and experiences shared;

1. There are definitely some issues with the carb. It's a stock Carter TQ that's been rebuilt a few times and I'm starting to think there's either a vacuum leak or perhaps I just don't know enough about them to keep it tuned properly. It runs fine at speed, but just won't stay idling.

Scott will make it perfect. If the body is warped, he can do something with it. New ones are available. Gets them tuned right on a mule engine;

http://www.harmsauto.com/

I just bought the 1901 Street Demon for a 318. 625CFM. Holley/ BG/ Demon makes a 750 Street Demon (1904)

If you go this route and you have metal line from your carb, Holley does not supply a reverse flare in a 5/16" with the kit. If your car has 3/8 steel line to the carb, you are fine, they come with that. Holley is the only one that sells the 5/16" reverse flare fitting, if that's what you've got, currently, to make it a clean install.

The carb will work with your air cleaner, no problem. I'd likely get Scott to redo the Carter TQ. The problems will go away. He just about has a monopoly on old TQs and does beautiful work. You can't go wrong, either way with that car, though. The Street Demon is a superior design, in my opinion, after going through mine for jetting and seeing the two, side by side, but you've got the next best thing that is dead nuts original, so that's why if I were in your shoes, I'd personally keep the TQ and send it to Scott.

2. Power steering box developed a leak at some point. This could be resolved by removing the box with the engine still in the car, but I believe most of the driver's side exhaust, steering, and the torsion bar needs to be removed to access it.

Pulled a leaky P/S box from a '73 Rallye Charger U code 440 resto about two years ago that was finished. If memory serves right, you go out from beneath, but I don't think the torsion bar comes out. Just the center link on that side and maaaaybe the exhaust manifold (which you're doing anyway). I know we had no issues leaving the engine and torsion bar in, though. Just fix the seal. Don't core it to some place. They will send you something in return that looks like it was dipped in tar and that crap doesn't come off easy.

3. There was a small water leak down the passenger side of the block. I still haven't pinpointed where it is coming from, but it started occurring after the engine overheated on the highway. It seems to have subsided for the the past year or two, but sometimes it happens after a short drive around town.


Rent/ borrow a coolant pressure leakdown kit and find it. Do this before you do anything else. You have to determine that the block is sound. If not, you need to get it stitched at the very least, at which point, I'd also pull the intake, leave the heads and examine the inner jacket walls. They are prone to cracking, but usually from freezing. No antifreeze in your oil tells me you just have an outer leak. Finding it is as easy as using a pressure kit at about 13-15lbs.

4. The exhaust manifolds have both developed small leaks around where the flange meets the head. They both also leak where they connect to the exhaust, but this may just be due to the crappy head pipes that my Dad had the local exhaust shop put on the car. I repaired the driver's side exhaust manifold leak by putting a new gasket on, but the threads on the exhaust studs were terrible and I could only tighten it so much before I feared they may strip.

Just replace the $2 studs. Vise-Grips and thread lock. Check the surface of the manfold and head and clean them up really well with a plastic gasket surface cleaning wheel, after you pull the studs and do both sides. Get sufficient head tubes, new gaskets on both sides and be done with it.

Moving forward, I feel like a good rebuild of the top end of the motor would help to eliminate any and all of these issues. I could also take the time to upgrade to a slightly more aggressive cam, possibly a new Street Demon carb (the new one that looks like the TQ reinvented), and possibly some TTI headers. I would be keeping all of the stock equipment obviously, but I really want to make the car more fun to drive without taking away from the value of the car (it's all numbers matching).

I really don't think you need to go this far. I think a large portion of your frustration with this car has directly to do with the small things that are wrong with it. The carburetor and a good tune (ignition included) will likely put a smile on your face, regarding how it performs.

I know the easy answer is a fix-all and to pull the engine, but believe me, on a car like that, you don't need it and it's way more work than what you set out to do with the engine in the car.

Consider this; in some likelihood, you may rebuild the engine and have to chase other leaks out of it, after the fact, anyway. I personally think that pulling the engine is time and money spent better doing other things.

I think you should fix the leaks, track the belt squealing and correct it, rebuild the carb and see how you like it before going cowboy on it. This is coming from someone who does it all the time and had to rebuild an engine, basically to exactly what you are talking about, Demon carb, new cam/ upper end and all and I only wish I could have done it in the car. It would have saved me a lot of time and unforseen problems.

Start small and move from there. If you have to pull it after trial and error, at least you'll have the carb tuned to go back on.
 
I don't know that I would change one nut or bolt on that car from stock. 72 is the year the least Road Runners were made. Being a factory big block makes it even more rare. JMHO.
 
Yep. I'd leave that carb right on top of it's intake after getting it perfect. Headers are for 318 cars. HP manifolds are fantastic on the street and won't bottom out everywhere.

The U Code 440 '73 Charger that I did the P/S pump replacement in, in it's color is something like, 1 of 1? That Roadrunner is not an easy find.
 
I agree with Dave Bonds and I have to say,why pull the engine and transmission? I have never done that before, even on FWD vehicles.
 
To find out which belt (or component) is squealing, pull one belt at a time. When it stops, you'll know. That new Demon carb looks great, but check the cfm. I thought they were only 625 cfm which may be a lot smaller than your TQ. Some of those were 800 cfm.

Tried that. Pulled all different combinations of belts. I think the only belt that didn't squeal was the Water Pump or the Power Steering Pump belt. Do you think it's possible the crank pulley is worn out and the belts are riding too low in the grooves?

Thank you for the suggestion though. It is a good one.

And the Street Demon 1904 model is a 750CFM unit with vacuum secondaries and an electric choke.

Thanks again.
 
I'm not quite on board with yanking the engine, but here are my thoughts and experiences shared;



Scott will make it perfect. If the body is warped, he can do something with it. New ones are available. Gets them tuned right on a mule engine;

http://www.harmsauto.com/

I just bought the 1901 Street Demon for a 318. 625CFM. Holley/ BG/ Demon makes a 750 Street Demon (1904)

If you go this route and you have metal line from your carb, Holley does not supply a reverse flare in a 5/16" with the kit. If your car has 3/8 steel line to the carb, you are fine, they come with that. Holley is the only one that sells the 5/16" reverse flare fitting, if that's what you've got, currently, to make it a clean install.

The carb will work with your air cleaner, no problem. I'd likely get Scott to redo the Carter TQ. The problems will go away. He just about has a monopoly on old TQs and does beautiful work. You can't go wrong, either way with that car, though. The Street Demon is a superior design, in my opinion, after going through mine for jetting and seeing the two, side by side, but you've got the next best thing that is dead nuts original, so that's why if I were in your shoes, I'd personally keep the TQ and send it to Scott.



Pulled a leaky P/S box from a '73 Rallye Charger U code 440 resto about two years ago that was finished. If memory serves right, you go out from beneath, but I don't think the torsion bar comes out. Just the center link on that side and maaaaybe the exhaust manifold (which you're doing anyway). I know we had no issues leaving the engine and torsion bar in, though. Just fix the seal. Don't core it to some place. They will send you something in return that looks like it was dipped in tar and that crap doesn't come off easy.




Rent/ borrow a coolant pressure leakdown kit and find it. Do this before you do anything else. You have to determine that the block is sound. If not, you need to get it stitched at the very least, at which point, I'd also pull the intake, leave the heads and examine the inner jacket walls. They are prone to cracking, but usually from freezing. No antifreeze in your oil tells me you just have an outer leak. Finding it is as easy as using a pressure kit at about 13-15lbs.



Just replace the $2 studs. Vise-Grips and thread lock. Check the surface of the manfold and head and clean them up really well with a plastic gasket surface cleaning wheel, after you pull the studs and do both sides. Get sufficient head tubes, new gaskets on both sides and be done with it.



I really don't think you need to go this far. I think a large portion of your frustration with this car has directly to do with the small things that are wrong with it. The carburetor and a good tune (ignition included) will likely put a smile on your face, regarding how it performs.

I know the easy answer is a fix-all and to pull the engine, but believe me, on a car like that, you don't need it and it's way more work than what you set out to do with the engine in the car.

Consider this; in some likelihood, you may rebuild the engine and have to chase other leaks out of it, after the fact, anyway. I personally think that pulling the engine is time and money spent better doing other things.

I think you should fix the leaks, track the belt squealing and correct it, rebuild the carb and see how you like it before going cowboy on it. This is coming from someone who does it all the time and had to rebuild an engine, basically to exactly what you are talking about, Demon carb, new cam/ upper end and all and I only wish I could have done it in the car. It would have saved me a lot of time and unforseen problems.

Start small and move from there. If you have to pull it after trial and error, at least you'll have the carb tuned to go back on.

Dave,
Thank you very much for taking the time to reply with all of this information. It's definitely helpful to see simpler solutions for all of the issues I listed.
I will get a call into Scott and see what he has to offer on rebuilding my carb. Thank you for that link as well.

-Mike
 
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