Having trubble starting engine

454Chevy · #1 10-31-2007, 12:44 AM

I have a 1978 gmc truck 1/2 ton with a 454 bigblock chevy. When I got the engine it was stock and it started in no time. I ported and polished the heads and swaped cam to street strip matching springs and roller rokers. Now I cant seem to start the engine it just crank and back fire a little. The engine is heavy to turn and it drains the battery in 5 to 8 cranks. do you guys know what could be the problem. Do you think the valves are to tight for the engine to turn?

Anything will help.

K10 · #2 10-31-2007, 01:02 PM

First of all, you should make sure you have your firing order correct for that motor. B/c the way you describe it, you turn over the engine, and it chugs, backfires, and stalls out. I would say that is a good place to start. If you installed matching springs and rockers, I don't see the valves being the problem. Good luck!

454Chevy · #3 10-31-2007, 03:46 PM

the firing order is correct I have a chilton book for that truck. Could it be the cam. the cam a bought was for a carburated engine but the engine was tbi.

2000CAYukon · #4 10-31-2007, 05:17 PM

Did you degree the cam? TBI does require the right cam to run right. Not sure if that would affect starting or not.

//2000CAYukon

454Chevy · #5 10-31-2007, 07:17 PM

Quote:

Originally Posted by 2000CAYukon

Did you degree the cam? TBI does require the right cam to run right. Not sure if that would affect starting or not.

//2000CAYukon

No i did not degree the cam compcams said it dose not matter. I took the engine from a suburban that was a tbi but I took that off and put on an edelbrock intake and a holley carb. the only thing a didn't do was adjust the valves I just tighten the nuts on the rocker arms.

maxwedge · #6 10-31-2007, 07:34 PM

How could you not adjust the valves? If they are too tight it will not start or backfire!

777stickman · #7 10-31-2007, 08:46 PM

MAX & YUKON are right on the money!!

#1. Cam timing is the backbone for engine performance.
#2. Proper valve adjustment is critical.
#3. Proper Ign timing is critical. (ref #1 as the dist is driven off the cam).

Good luck.

2000CAYukon · #8 10-31-2007, 08:58 PM

Did they recommend straight up, advanced or retarded? Is this a mechanical or hydraulic? Flat tappet or roller?

Since it is heavy to turn, the valves may not be opening enough (or at all) or the timing is off (ignition or valve).

//2000CAYukon

454Chevy · #9 11-01-2007, 12:07 AM

Quote:

Originally Posted by 2000CAYukon

Did they recommend straight up, advanced or retarded? Is this a mechanical or hydraulic? Flat tappet or roller?

Since it is heavy to turn, the valves may not be opening enough (or at all) or the timing is off (ignition or valve).

//2000CAYukon

Sraight up. hydraulic flat tappet. I think is the valves I will work on it this weekend I just get to lazy to do the valves but I will try and if I start it I will post the video. Thank you guy.

p.s.

Any one know where to get instructions on how to adjust the valves

robnoxiousauto · #10 11-01-2007, 12:28 AM

to adjust valves on a chevy w hydrolic lifters i do it one valve at a time due to valve overlap etc i find it easyist to turn the motor over by hand untill the exhaust valve is opened on a given cylinder then tighten intake valve to zero lash which is when u can not move the push rod up and down freely then turn and additional 90 to 180 degrees. as for motor not wanting to turn over freely did you change the ratio on the rockers and did u check that the valves are not actually hitting the piston? i do this with no head gasket and a solid lifter i install the clyinder head with a couple head bolts snugg and silly putty on top of the piston i then adjust valve to zero lash i then turn motor over 2 complete revolutions. i then remove cylinder head and check silly putty u need to have atleast 10 thou with the head gasket being 40 thou you will have 0.050'' clearence. as for tbi with a cam you will have some runability issues if the cam is over an advertised duration of 180 degrees because low engine vacum will cause high map voltage which will cause poor idle and may run fat with map and fuel trim codes any more questions u may email me direct at [email protected]

2000CAYukon · #11 11-01-2007, 12:43 AM

http://www.chevyhiperformance.com/te...nfo/index.html

This is a very good write up on adjusting valves.

//2000CAYukon

robnoxiousauto · #12 11-01-2007, 01:55 AM

Quote:

Originally Posted by 2000CAYukon

http://www.chevyhiperformance.com/te...nfo/index.html

This is a very good write up on adjusting valves.

//2000CAYukon

thank you very much have had hard time describing some tasks that have been doing for years but appreciate the positive feed back.

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