Polyurethane motor mount melted during break-in

[389Z]

Anybody ever have this happen? I did the break-in for 25 minutes and never got above 180 degrees with good oil pressure, etc., but man the headers were aglowin'. A few small oil leaks caused some smoke, but all went well. When we rolled it out again, we noticed some red melted plastic on the ground and were stumped until we looked underneath. The passenger side polyurethane motor mount (got the red ones to match the chrome/red engine build) melted slightly enough to leave a couple of drops on the garage floor and a three inch string hanging down. It doesn't appear to have affected the mount as it is still solid and doesn't move a bit, but it seemed very strange. My buddy who has about seven SBC builds under his belt had never seen/heard of it and thought I would pass it along to you guys. My guess is the header heat caused it coupled with the 10:1 383. I am continuing to watch it and no further damage so I am figuring it is just another break-in thing. Anybody ever seen anything like this on polyurethane mounts?

 

Also did the maiden drive and the 383 is like a new car compared to the old 350. Nothing too radical as we still needed to rework the lash and finish the carb tuning, but everybody I drove by just stood there slack-jawed as I motored past. Nothing sleeper about it...

 

Bill

[Poundz9oh9]

Wow, never heard of that. Those headers must have been H. O. T!!! I don't think they're supposed to get that hot if your motor was running right.

[COZY Z COLE]

Glowing headers.... The two main reasons are a rich mixture and late ignition timing i.e. the fuel doesn't have enough time to burn inside the combustion chamber.

 

 

 

 

LARRY

[1 tuff z]

i thought that a 'too lean' condition was the reason headers would get too hot [not enuf fuel to keep the engine cool]?

[e_racer1999]

i thought that a 'too lean' condition was the reason headers would get too hot [not enuf fuel to keep the engine cool]?

 

that's the case with the motor running hot. if there is still fuel left to burn in the headers then it's basically a second combustion chamber.

[naviathan]

that's the case with the motor running hot. if there is still fuel left to burn in the headers then it's basically a second combustion chamber.

Oh no, I've cherried an exhaust manifold (i.e. cast iron stock manifold) on a toyota 22R by running too lean.

[Pop N Wood]

Yeah, I have always thought that high exhaust gas temps are from running too lean. That is what all the turbo guys say.

 

Need to get this right so I don't burn off the ceramic coating from my headers on startup.

[COZY Z COLE]

Here's a couple more reads...

 

http://www.auto-ware.com/autoware-bin/techarchive.pl?noframes;read=6433

 

http://racingarticles.com/article_racing-56.html

 

And yes I've seen a too lean condition mentioned by people. It's seems timing problem is agreed by all but a rich/lean condition is still being debated.

 

 

LARRY

[naviathan]

Not to argue, but the 22R I cherried the manifold on was fine after richening the mixture. Running a rich mixture can cause fuel to burn in the exhaust, but usually that only makes a popping or backfiring sound and doesn't really create any more heat than is already there. Excess fuel will "wash" a cylinder causing it to cool. Hence the reason Harley's ignition modules will shutdown cylinders when the temps get too high. No spark no fire, cool fuel washes cylinder, reduces temps, bike stays running (although a bit rough and slugish) and nothing warps. fuel burning in a manifold isn't hot enough to cause the manifold to heat up to cherry red. It's no longer compressed once it's pushed out the exhaust thereby making temps lower than in the cylinder. Lean however will superheat the air left in the cylinder and blow it out the exhaust causing the manifold to heat. Heating the manifold and the internal cylinder temps causes the engine to run hotter in general and I've even seen it burn holes in pistons, melt valves and deform exhaust headers. Perfect example of too much air not enough fuel and the effects on metal. Look at an Oxy/Acetylene cutting torch. regular mixture heats the metal, but as soon as you hit that extra oxygen it melts and blasts through it. The Acetylene is the fuel, the oxygen helps it burn just like gas in a cylinder. You increase the amount of oxygen over the amount fuel and it get super hot. Anyhow, sorry to ramble.

[LLave]

huh... polyurethanes dont melt until something like 400 degrees F. I wonder if there was some red coating on the outside left over from the manufacturing process. Then again, if the headers are cherry color they are in the 1400 degree neighborhood.

[heavy85]

I thought cherry headers were normal if under heavy load or elevated idle such a during break-in ... at least one's I've seen on the dyno do? I thought this is one reason header manufacturers say not to use ceramic coated headers during break-in as the coating hasn't fully cured and the high heat will damage the coating. At least that's what the JTR (Sanderson) headers say.

 

Cameron

[389Z]

I would definitely say it was burning rich during the break-in with no real tuning other than idle and of course the 2,500 - 3,000 rpms for 25 minutes is a much heavier load than normal conditions air-flow wise (too busy looking for fuel, coolant, and oil leaks to mess with the carb settings). I expected the glowing headers during break-in, but the melting motor mount was a little freaky. It is really not misshapen or out of altered as a result, just singed. The driver side was unaffected so that would tend to rule out the coating, but who knows. It doesn't seem to be happening now under driving conditions and I have no experience with urethane motor mounts, so I wanted to throw it out there just in case you guys had seen it before and could tell me to relax. Seems like all is well. I will follow-up if anything else develops. Just when you think youv'e see it all......

[Teekass]

Leaning the mixture will cause the exhaust gas temperature to increase, but only to a point....continuing to lean past that point will actually cause the EGT to decrease. I learned this during my days of flying piston powered airplanes. Airplanes have a mixture lever that directly controls the amount of fuel going into the engine. When you set cruise power, you lean the mixture while watching the EGT gauge. The EGT will go up to a peak, then start to come back down. There is a second needle on the outside of the EGT gauge that you move to mark what the peak EGT temperature was (normally around 1,500 degrees F). Most people set the mixture at the peak, then richen the fuel until the EGT drops 50-75 degrees F (known as "rich of peak"). Another method is to lean the mixture 50-75 degrees "lean of peak".....better fuel economy but expect to replace cylinders more frequently.

 

With all that said, my guess is that a lean mixture alone wouldn't cause an abnormal amount of heat in the headers.

 

If you get bored, look at this airplane engine....I'm always amazed at the displacement of airplane engines......550 cubic inch 6 cylinder .

 

http://www.tcmlink.com/EngSpecSheetDocs/TSIO550C.pdf

[bjhines]

I have to second Teekass on that. My limited experience with both Airplanes and an EGT I have used to setup my triple Webers shows that you can peak EGT and then find that it will read lower than peak if either too lean or too rich. I also run multiple O2 sensors for A/F ratio monitoring. The off-peak EGT correlates well with too rich/too lean A/F readings. When timing is seriously retarded the EGT will suddenly JUMP to far higher than normal EGT readings.

 

I don't doubt that there are some siuations that can cause the headers to glow besides retarded timing.