headers glow on fresh motor

[mini64]

Just freshened my twin cam (bearings, rings) and put it back in and upon starting it within a minute the headers are starting to glow at the first bend out of the head. In two minutes they are glowing all the way down to the bottom bend. I shut it off at this point before they get too red. What have i done wrong?

I've double checked my cam timing. Running the exhaust a couple degrees less BTDC then is optimum, but nothing i havent done before. I'm keeping the rev's close to 3000rpm, as a rebuilders book i have always gone by says i should. Here the dstributor timing is about 20 degrees, although i backed it down to 15 once but no change. I havent run it long enough to check mixture on the plugs. There is some wetness on tops of the pistons, possibly oil from installing the pistons, but odly zero smoke out the tail pipe so maybe it is fuel (running webers) on the pistons. I should note this is a race motor and the headers are non-stock, larger diameter and somewhat thin wall, but i've never seen the glowing before. Then again, i didnt have them on last time i rebuilt the motor.

The bores are a bit oversize, this being the second time they were rigid-honed for new rings, so the piston-bore clearance and ring gaps are larger then they should be.

I do hear a funny exhaust leak puffing sometimes. Could that be pinging. Its hard to say as everything is so loud without a muffler. But then i had started hearing this noise just before the rebuild and had hoped new exhaust gaskets would cure it.

Could the head gasket be incorrectly positioned so that the compression rings are overhanging the bore and getting hot (worse yet could the nose be them getting hit? - nah, i heard that noise before).

This was a rush job and i didnt properly de-carbon the pistons or valves. I soaked the pistons overnight in carb cleaner, washed them off, then lightly rubbed the remaining carbon but a lot was left on. In fact I probably put some rough edges in the old carbon that could be glowing?

any theories would be appreciated. Just glowing exhausts wouldnt be that bad, but not so quickly!

[Frank Howard]

Fuel mixture too lean?

[c.d.s.]

Hello,

Please re-check your timing again as it may be to retarded.

Also, your fuel mixture to may be too rich, thus fuel is burning in the headers.

That would explain the wet pistons and the glowing.


regards


cds

[John Larkin]

I managed to make my exhaust headers glow once after an engine rebuild --- I had set up the timing on the wrong TDC of number 1 piston so I was out by one full rotation of the crankshaft.

John Larkin

[mini64]

thanks guys. I'll recheck timing again, both distributor and cam. but i always do a visual on the cams making sure the lobes for number one are more or less pointing out at tdc. this is correct, right? I havent messed with the mixture and havent run it long enough to do a plug reading (they look fine so far).

[denicholls2]

It's already been said, I second it. Unburned fuel ignited when it hits the headers is the most likely cause.

While the engine itself will run hotter with a lean mixture, the headers won't be significantly hotter than the engine under this condition. Too rich and they will.

Timing is a factor, but the poster who claimed they timed for 180 degrees out doesn't understand the mechanics of a 4-cylinder engine. TDC is TDC; the only difference is whether the piston is firing on the power or the intake stroke (distributor timing.) If the spark is timed 180 camshaft degrees out, there's no way the engine will run, let alone make its headers glow.

[John Larkin]

I believe that I do understand the mechanics of an engine. There are two TDC positions for each piston in a four stroke engine --- top of the compression stroke and top of the exhaust stroke. The number of cylinders makes no difference.

I had set up my timing based on the incorrect TDC of No. 1 cylinder --- in other words I was wrong by one full rotation of the crankshaft, and so sparking just before exhaust TDC.

One full rotation of the crankshaft is 360 degrees, and not 180 degrees.

John Larkin

[Petter Hval]

360 degrees crankshaft rotation is 180 degrees rotation of
the camshaft and the dizzy rotor.
Petter

[rdssdi]

I had the same problem. I solved the problem by adjusting the timing, "freeing" the advance mechanism and opening the idle mixture screws and balancing the carbs.

Bob

[mini64]

checked over everything and adjusted the exhaust timing by about 2 degrees more retarded. then just went into my normal run in procedure and all seems fine. Maybe it was just the combination of thin headers and holding it at 3000rpm with no airflow coming in. i dont know, but thanks guys!