1989 SBC in and hooked up, issues cranking

[Jason_l]

OK, recently I took my 89 TBI motor out of a old truck to go in my 1981 GMC. Motor was switched to carb some time ago and always ran great. So I put the SBC in my 3/4 ton, the motor turns n stops, turns n stops. I removed sparkplugs and motor rolls free and distributor is putting out spark. Once plugs are placed back in it does the same , roll n stop ...all connections seem well and have took off to clean and check but it all seems good. Even tried a different starter and it does the same thing. Rotor turns with engine as it should, rods n valves seem to move freely as well. So what happens? Motor was a strong runner for years and I did nothing but put in a different truck. Could timing be off enough to build compression and stop due to timing? I've never had one stop,roll,stop roll.

[Jason_l]

Distributor was off a tooth. Truck starts n runs. Thanks guys

[Doug_Scott]

The first thing that comes to mind is pretty simple. Pull the power wire from the distributor and see if the engine cranks over normally. If it does, you have the ignition timing too far advanced. With the plugs out of the engine, all that does is allow the air to be expelled instead of being compressed. Given that the engine was swapped without the heads being removed, the only thing that can stop the engine from cranking like you describe is too much timing.

This also assumes that when the engine is cranked over with the plugs out, that there is nothing coming out of the spark plug holes, like water/coolant.

 

NOTE: just thought of one other possibility, verify that the spark plugs are the ones for the actual engine, not the truck's original engine. If the plugs are causing the interference you would see damage to the spark plug.

[Jason_l]

Same plugs are in that were in it before. That was my plan, don't touch anything cause it was a runner, just wanted to drop it in, make sure it ran and then tuneup and eliminate vac hoses. That's why I'm stumped. Didn't even touch the distributor and it hasn't moved. That's why I figured something with timing being that it's building compression and valves aren't opening soon enough to relieve compression . frustrated cause its gotta b simple unless chain jumped

[Doug_Scott]

If the timing chain has jumped a tooth or two it would also put ignition timing out. Easy enough to verify, just follow Jsdirt post on checking timing, but you can stop at setting the timing marks at 0. Once there check and see where the rotor is pointing. It will either be at number cyl #1 or at cyl #6. It should be very close to being right at that point. You can turn the engine to show 10 degrees and see if it is directly at either #1 or #6.

[Jsdirt]

The distributor may have got bumped without you noticing. I've seen it happen many times. GM's with that thing right next to the firewall, it's real easy to whack it, and either crack the cap or twist the whole unit several degrees one way or the other.

 

Another possibility is that the cap and rotor just got a little corroded from sitting a while. Did the engine sit outside in the weather any length of time, or just sit idle in high humidity? I've seen an old cap/rotor make an engine stop while cranking, like the starter didn't have the power to turn the engine over.

 

Doug beat me to it - whenever an engine does that while cranking, 9 times out of 10 it's firing too soon (too far advanced).

 

Wouldn't hurt to throw a light on it just to verify. Just mark the TDC line on the harmonic balancer with Wite-Out, or a white paint pen so it shows up nice and bright, and clean off the timing tab with the degree marks on it, and highlight 10° BTDC - you'll want to be right around there. Just cranking should be enough to see where your at.

[Jsdirt]

Good deal.

 

Sometimes when they're off a tooth, you can just twist the distributor WAY over to compensate, but that usually limits your adjustability, especially if it's got a vacuum advance hanging off it. But if you have room to get the timing where it needs to be, technically you can leave it that way without having to yank the whole thing and fiddle with the oil pump indexing.

 

I actually had to go a tooth off on my '89 S10 Blazer when I dropped in the '00 engine, to get the advance unit out of the carb linkage. Not a whole hell of a lot of room on those S-series trucks, especially with a true Vortec sitting in there ...