I'm just putting a rebuilt motor back in my truck and have a question about the distributor. The truck is just backfiring when I try to start it, making me think the distr. was 180 degrees out. But, I had someone turn the motor over while I left my finger on the #1 plug hole. When it blew my finger back I looked at the rotor and it was just before the #1 wire on the distributor cap. With a couple more starter bumps, the piston was at the top and all looked ok.
I did have the external coil (HEI)mounted on the inner fender and moved it to the block. During those few months the motor was out, the wires were unhooked from the coil. Is it possible the wires are reversed? I hate to turn them without knowing as one of the three wires is for power.

Any advice?

Check the firing order and valve adjusment first.

Good luck

I looked and the coil wires will only go on one way, so I know I have them right. I tried to rotate the dist. 180 degrees but it won't fit because of the vacuum advance hitting the block.

John, By checking the firing order, you mean the location of the wires..i.e. 153624? It is a 250 I6.
They ran the motor at Jasper where it was rebuilt. Would they have made valve adjustments then?

Who knows??

Run a compression test & put the dist back in the way it was. It sounded (by what you said) like that was okay.

Is it backfiring out the carb or exhaust??

Also; make sure It's dry inside the Dist. HEI hates any moisture. Make sure the power box is grounded good.

Is there a ground strap from the engine to the body??

Backfire is out carb. I don't have a ground strap from the motor. The coil is mounted to the block, so that could be a issue. I'll add a ground tomorrow and see what happens.

The Vacum advance Should be Facing Forward Or slitly to the water Pump. The Way You rotate the dist. Is to Pull It up JUST enough to be able to rotate The Rotor Button NOT the whole dist.
Each time the Piston come TDC it will want to push you finger anyway,JUST will have More Push because the Valves will be closed at that time.
The back fire out the carb does mean your 180 out
The ground strap from motor to chassi will not cause the carb to backfire(well NOT that I ever heard of)IF you want to be 100% sure you Valve are closed at TDC Pull the valve cover and Watch the rockers(if you don't have a dail gage)Then check you dampener to see if it is at Zero Then set you dist in at #one plug.If all is right It should fire right up No back popping anywhere (carb or exhaust)

>When it blew my finger back I looked at the rotor and it was just before the #1 wire <

Before you look at the rotor, look at the timing mark. You said it's a rebuilt engine, so you know the balancer is good and the timing mark is correct. Right? You are on the compression stroke so the timing mark should be real close to TDC. Turn the crank by hand so that it is sitting on about six degrees. The rotor should now be pointing to the #1 post. Pull the #1 plug wire off and put an old plug on the wire. Turn the key to "ON". Rock the distributor back and forth until you see the plug fire and try to stop at that spot. Replace plug wire. Snug distributor. Start engine.
Run for 20 minutes at 1500 to break in cam. Refill radiator as it heats up. Drop to idle, set timing with light, adj carb idle mix and idle speed. Recheck timing and go for a drive.

Thanks for your responses guys!
Walt,

The distributor I bought, I think from Langdons. It is made for an external coil, however I did have the coil on a previous motor and place it in a different spot on this motor and probably had the distributor cap off at sometime and could possibly have put it back on differently. Can you help me understand how to index the distributor?

Twisted,
My vacuum advance is pointing toward the rear. I have set a few distributors in (only a few) and probably have just been lucky on those, as I'm not sure I understand exactly what the process is. I'm a shadetree mechanic and have problems on occasion because I take everything literally and have difficulty understanding things when I know the procedure but don't understand the 'whys' of it. I understand the placing of the cylinder at tdc and know the distributor should fire at that point on the #1 cylinder. I don't quite get the part when the distributor is set in the hole with the rotor pointing to #1 cylinder, but the top part of the distributor can be moved. I think maybe I don't understand the relationship between the bottom an the top of the distributor,

Thanks again guys!

to paraphrase,
Take the valve cover off.
Turn it over until you see the #1 intake valve close.
Then look for the piston to come up to the top.
Thats where the timing mark and the dizzy should be.
Once its running, you use the timing light to dial it in.

Okay; I guess it was in wrong as Larry said.

Walt's description is right too.

Put the ground strap on anyway, even if it runs W/O it etc.

Good luck.

John,

I think it makes good sense to have the ground strap on. I'm looking into where to attach that.

Walt,
Thanks for your help. I now get the part about pointing the rotor at #1 piston. It could be any point, but that is just a good reference.

I followed the procedures all you guys gave today. Soon after, I fired the motor!! I have abusy day tomorrow, as the fat man comes tonight, but have some time off work till after the first of the year and am looking forward to spending some time in the garage.

John, gearhead, Walt, Twisted, Richard;

Thanks for all your help. I frequent several boards, but really hope to keep this truck INLINE. It's always nice to ask a question here and get some professional input.

HAVE A MERRY CHRISTMAS!!

Just wanted to let you guys know I got it in, set the timing and the thing purrs like a kitten. Thanks for your help!!

SixPac

Bob