707C engine 1970 R 608.

[mackdump600@yahoo.com]

Hello I have a 7707 c that exhaust temperature melts the Pistons rebuilt the motor 40 over new pistons rings and it’s still running hot put a pyrometer on it ,tried drilling out the jets in the carburetor it’s still running way too hot ,unless I pull the choke out better than halfway to keep it temperature down any advice is this common with them or should I put a four barrel Holly or anything else on it. It is the original carburetor yet

[mowerman]

Yes it sounds like it’s almost running to lean. Maybe radiator  needs flushing. Or faulty thermostat. That’s all I got good luck.

[mowerman]

Years ago, I had an issue like that with a Chevy pick up. Turns out the water jackets were full of stop leak.

[mowerman]

It was all caked up and they’re like silly putty

[1958 F.W.D.]

What fuel are you using? 

[mackdump600@yahoo.com]

I’m using regular 88 fuel with the 10% ethanol in it it’s about all I can find around here the water temperature doesn’t go up it’s exhaust temperature melts the pistons

[mowerman]

Sorry, but I’ve run out of ideas that sucks

[mackdump600@yahoo.com]

Thanks 

[theakerstwo]

Sucking air in the intake as well as fast timing will run exhaust temp hi also.Also hi compression due to over surface head or block is not good for it.

[Joey Mack]

I was wondering about trying to suppress this heat..  I understand what Glenn posted and I agree.. Can you retard the timing a couple degrees?  I also thought about the alcohol/water injection I had on my '69 Camaro..  would that help turn the heat down ?  It's been a long time for me, so there is a chance I forgot a detail or two..  But, I think about a timing adjustment first..  If I were an engine,,,,  I would rather be wimpy, over being burned up..     jojo

[theakerstwo]

That engine does not time fast so maybe the timing marks are incorrect.

[theakerstwo]

I was thinking it timed at 8 degrees

[mackdump600@yahoo.com]

• Hi  I thank everybody for the answers .the timing is part of the problem the first time the engine blew I did   Have the timing advance too much the book and I have the original book calls for 2° and that’s what it set for with regular fuel I have a pyrometer on it now to keep an eye on the internal temperature of it but it’s still getting too hot I’ve triple check the Intake for vacuum leaks nothing there in process of drilling out the jets on the carburetor but it’s slow going and with winter I don’t get a chance to run it that much thanks everybody for all the suggestions will keep you informed merry Christmas

[steve s.]

It is more likely that your timing is retarded than too far advanced.  When the spark occurs late, fuel can still be burning as it makes its way out the exhaust. Maybe you could set your timimg with a vacuum guage.  Or do it by ear. Just advance the timing as far as you can without getting spark knock under load. The timing marks don't seem to be helping any.  I doubt that the carburetor is the problem unless it is the wrong one for your engine. Pulling out the choke to make it run cooler is strange. Drilling your jets is not a normal repair for anything. The alcohol/water injection is a good idea, and will allow you to advance your timing more, but you really shouldn't need to add it. Another thought is that your cam timing could be off. Good luck

[theakerstwo]

He is saying it melts the pistons.Fast timing puts more heat in the pistons because the fire is on top of the pistons longer with fast timing.Slow timing is a cooler piston but hotter valves a exhaust is hotter after it leaves the heads.

[mowerman]

Well, I hope this cures your problem. I also thought cylinders may have been over bored . But I am sure the temperature gage would also read high best of luck, partner bob 

[mowerman]

 gasoline mixture too high or too low. I’m sure somebody else already brought that up.Bob

[mowerman]

I was just kind of curious do you have any problems getting electrical parts for that engine? Bob 

[mackdump600@yahoo.com]

Hi  not so far, I also have a 49 Chevy 4400 series 235 six cylinder and it takes exactly the same rotor cap and button as my Mack ,also the per Tronics was the same as I put in my Chevy . everything else is just Standard  turn signal relays. I changed it over to negative ground from positive and  only had to reverse the wires on the temperature gauge and it still works today , went to a one wire alternator and did away with everything else on the old charging system in 04 and haven’t had a problem with electrical at all .

[mowerman]

Excellent I knew you were going to say that about some of the ignition parts. I’m thinking of doing the same thing with mine going to negative ground  with a auto generator or alternator I put an air starter in it and that illuminates a lot of unnecessary parts four 6 V batteries, for example parallel switch and so on   And some doped up ass clown lifted all my battery cables while I was in the hospital with back surgery 11 years ago. No I don’t know what to do with what is left or how to hook anything up… Bob

[mowerman]

It sure helps out when you can just walk in to your neighborhood auto parts and buy a lot of stuff for it… Bob

[doubleclutchinweasel]

Just went back and re-read the original post.  If pulling out the choke cools things off, then it definitely sounds like a lean mixture.  But...

I think everybody here has listed all the normal issues.  Inadequate cooling.  Intake leaks.  Lean mixture.  Timing too advanced (hot piston/detonation).  Timing too late (burns exhaust valves).  Fuel octane (too low = detonation, too high = burnt exhaust valves).  There are only a certain number of things here to look at.

I'll be curious to hear the eventual solution, as I'm sure all the others will be.

[MorrisMe]

I agree with all the above as well, and since you rebuilt the engine that would eliminate your block and heads being plugged up (provided the block and heads were hot tanked).  Exhaust valves should have been replaced / reground, and new exhaust gaskets ect, (example: running with a bad exhaust valve could cause burnt piston).  Sounds like you have addressed all of this.  So...

Too lean fuel mixture = hot combustion.  Factory carburetor, are you sure this is the right carb?

retarded timing = hot exhaust valve and manifold.

Combination of both = extra heat.

only other thing could be head gasket.  I am not familiar with this engine but is it possible that the head gasket is on backwards or upside down, not allowing sufficient / improper cooling in the head?

Stock from the factory engine and carburetor should all perform correctly and drilling jets / pulling choke would only be a bandaid for actual problem in most books not actually fixing the real issue.  If the carburetor was at it's maximum flow capability from the factory then a .040 overbore could be overtaxing your fuel delivery. (requiring jetting and usually air flow as well.

check fuel pump pressure, all factory fuel lines / filters, to make sure fuel is being supplied in the correct amount.

[mackdump600@yahoo.com]

Thank you for trying to help me I will double check everything again water temperature does not go up ,its exhaust temperature with the pyrometer goes up extremely fast when it starts to lug down, went up a heat range hotter on the spark plugs haven’t been running it much yet to see if that helps I appreciate the thought have a good day my friend will post when I find a problem