Chris_1

iTrader: (1)

Just the chain like sdmartin suggested would make a big difference - even a stock one - at least as far as getting it back to where it was originally. When the chain starts to stretch a little the valves will be opening and closing at a slightly different time than when they're supposed to. Pulling that back to where it belongs goes a long way toward bringing back that original crisp throttle response.
As for the coil, it seems like sticking a non stock coil in the middle of the stock ignition system tends to make the other components in the system start to fail. The stock ignition system seems to be generally pretty reliable just the way it came.

Gcs

Thankyou that makes a lot of sence. Is there any way of telling if the chain is streached. Any inspection hole or anything like that. The truck came from a Clas b dealership with no mantainence records. Maybe the chain got replaced. The truck shows good mantainence.

Chris_1

iTrader: (1)

Not likely to have been replaced, but if it were you would see new gaskets on the timing case cover.
If you want to get an idea of how much slack your chain actually has, you can put a socket on the crankshaft bolt and a long bar. You can then turn the motor back and forth, the crankshaft and pistons will move fairly easily but when the chain tightens against the cam gear you'll feel quite a bit more resistance. Rock it back and forth from tight to tight and note roughly how many degrees the bar will move.
When the chain was new that would be zero to maybe a few degrees. 5 is still pretty good, even 10 degrees is not too bad - get to 15, 20 or 25 degrees and you can start to see how far your cam is out of sync with where it's supposed to be in relation to the position of the piston ;;theoretically it's only out 1/2 that much since you're checking slack in both directions and the chain only turns one way (just to clarify) but still - if the cam is out 10 degrees then the valve is opening a lot later than it was originally designed to do; it's also closing later than it's supposed to too.
Hopefully you can see how any signifigant amount of slack in the chain would seriously hurt potential performance.
It's probably recommended that the battery be disconnected before you stick your fingers in there; at the very least I'd make sure the truck was off and I had the keys in my pocket ! (Always play safe )

Gcs

Thanks again for that valuable information. As I don't want any deficiencies, I think it best to do both the rv cam and timing chain. I did not realize that the chain stretching would have a detrimental effect. Probably would do the cam bearings while I am at it. I assume all this cam be done with the motor in the truck.

hobolabo

Thanks Chris_1 for the great explanation on the timing chain. I'm currently working on my 78 build with a stroked 351M that has about 75k on it, gonna check for slack while its out.
Great explanation!