I bought a used 1979 SBC 400. Seller told me it was a good runner. I pulled it from a motorhome. After some checks it did shown pretty decent. I bought and cleaned it up. Did some maintenance and upgrades and put it in my 1980 Vette.

I installed a new timing gear and chain set.
Installed headers.
I installed an Edelbrock performer intake manifold.
I cleaned up and installed a 1975 Quadrajet.
I installed an MSD Street Performer HEI dist. Assy.

After assembly and installation the engine fired up quickly but sounded pretty rough. We played with the timing and air idle mixture screws. Things improved but it still ran pretty rough. It wouldn’t rev up smooth or make good power. I double checked all my spark plug wires, all are new and in proper position. More screwing with the timing led me to believe that’s not the issue.

The quadrajet definitely is problematic. It’s certainly over fueling. Even leaking fuel. Pooling in the manifold divots. I checked fuel pump pressure its a new pump. It makes 7.5-8 psi. I will get the Quadrajet dealt with. Yet I was thinking maybe I am out 1 tooth on my timing chain? A few times while adjusting the timing, when cranking the engine over to start, it pushed a good shot of compressed air up through the carb. Spraying raw fuel out of the venturi into the sky. Hmm. Again I am thinking, maybe valve timing is out.

I just pulled the front end apart and checked my timing marks. Seems to be bang-on. With distributor rotor pointed to #1, timing marks are lined up (spread apart, both dots at the top of their gears, lined up). I took valves cover off and confirmed valve movement. Checked tension at rockers. Both valves are definitely closed. #1 is at TDC. I feel like my distributor and timing gears are all lined up.

Here’s the weird thing: with the timing light connected to spark wire #1, when the engine is running, the flash of the timing light is picking up the harmonic balancer mark at about 11 o’clock when viewed from the front of the engine. It should be over al about 2 o’clock. I’m thinking, hmm. Harmonic balancer has maybe slipped? Or maybe slipping while the engine is running? I can see the rubber has a few small cracks in it. No obvious signs of it coming a-part or slipping. It is the original 1979 balancer. I have ordered a new balancer. It’ll arrive in a few days. That should eliminate that variable. The timing light I am using is old school. On off. No adjustments.

With the balancer removed here, right now #1 is at TDC. Gears lined are up. When I slide the balancer on the crankshaft the timing mark is at 2 o’clock. Where I expect it to be. Weird. Why does my #1 spark plug seem to be firing so early? My distributor might be out one tooth? Am I on the right track here? Yet we twisted the distribution a lot in both directions when trying to clean up the rough running. Engine running didn’t improve much.

Next point:
I am looking here at #1 TDC all lined up. Harmonic balancer is at the 0 degree timing mark. That all looks good. I locate and find #1 spark wire boot at the distributor. I remove the distributor cap. The Rotor is about half way between wire 1 and 2. Well past where I think it should be. I believe it should be at #1. I thinking I need to pull distributor and set it back a tooth. Am I on the right track here?

2 things going on here and are separate issues. The carb will also be addressed.

Your comments are appreciated. Thx.

 

It sounds like you have it assembled correctly. Might the poor engine performance be caused by the overly rich fuel delivery and who knows what else is going on with the carb?

#1: I think you should borrow or rent another timing light to make sure your light is working properly. No dissing intended: are you testing TDC and connecting your light to the plug wire on the forward-most driver's cylinder?

#2: When you said the rotor was half-way between 1 & 2, I want to make sure I'm understanding: The #2 cylinder fires immediately before #1 - was the rotor between these two? #8 fires immediately after #1 - was the rotor between these two? The only time I'd restab the distributor is if there isn't enough room to swing the distributor to get the proper timing.

Maybe post a photo of the top of the engine without the air cleaner.

 

Thank you for the reply. I mistakenly said my rotor was between 1 & 2 distributor lugs. I meant to say it was about half way between 1 & 8 distributor lugs.

I was reading timing off of cylinder #1. Front left drivers side of the engine.

My problems could very well be 100% carburetor induced. I ordered a new rebuild kit. I’ll give it a shot this week. If it is still a problem, they stock brand new Edelbrock carbs just down the road. If I get yo the point of having enough of the quadrajet, that’s what I’ll probably do. I’ll try posting a photo of the top of my engine tomorrow.

 

damper for 400 sbc is unique unto itself. Its outer ring has a large cast-in imbalance that should be prominent.

Do you have access to the OE 79 Qjet for your 400 ?

 

The timing tab needs to match the mark on the damper. Some original applications moved the timing tab and marks closer to 12:00 where it would be easier to see during service on other ( non-Corvette) chassis. You may have a mismatched pair.

 

A few photos as requested:

 

The engine was pulled from an 1980 1T Van (RV) chassis. The 6.6L was dated 1979.


My 1980 Corvette was purchased with a blown engine. I decided to use the carb that was on the blown engine. That Quadraject SN indicates its from a 1975 Corvette with manual transmission. My 1980 has an auto transmission. I do have the original 1979 Quadrajet carb that came on the 400. I could try using it.

I am in Canada. I could send either carb to Lars. It may be cost prohibitive. Also down-time considerable, during prime cruising season. This is why I am leaning towards a new Edelbrock here locally. I’d be up and running in a couple hours.

 

If it were mine (it's not) I'd limp-thru this season w/ best carb on hand. Then, post-season: send best Qjet out for Pro overhaul. Nothing stops you from DIY freshening what's on-hand.

From my perspective, bolt-on Edelbrock seem to be a crap-shoot. Some are great; others rather not.

 

Check out @stingr69's answer to this other '79 timing mark question that sounds just like what you're asking.
https://www.corvetteforum.com/forums...post1597274107

When aligning timing chain marks, I find it easiest to place the engine on #6 TDC compression stroke. This puts the crank dot at 12:00 and the cam dot at 6:00 and just an inch apart. (also from the thread link above)

 

Thank you. Yes I confirmed dot to dot line up with both dots close, about 1” apart. Also the dots spread wide apart and lined up.

Reading the articles about people having mis-matched harmonic balancers and timing markers. I agree I likely am experiencing this. What tool are people using for a tool to stop the piston travel in forward and reverse? To manually confirm TDC. Feels like that might be a fun project.

One other point I thought about. Might have Inset the valves too tight. With each valve closed, I turned the rocker bolt just enough where I could not feel any movement in the push rod. Then I turned the rocker nut another ½ turn. Effectively pre-loading the hydraulic lifter I assume? Thx.

 

if that’s where the rotor button is when you’re at TDC you’re off a tooth. It should line directly up with the post on the cap. You should be able to lift the distributor just enough to disengage the cam gear but still have the oil pump shaft follow along. ‘Walking’ it to where it needs to go.

 

Pro Form piston stop tool 66792 about $14

 

I wouldn't worry any more about the timing chain if you checked both positions.

The Summit tool would be fine; a lot of folks use whatever is at hand. A wood dowel would work well - 3/8" - it's soft so you're not going to damage the piston. That said, whatever you use, come up gently to contact the stop.

The feel for preloading hydraulic lifters is a pretty subjective thing with a couple of caveats. Not feeling any movement could well be too tight if you're talking about rotating the push rods. "No movement" is really aimed at removing the up and down gap between the push rod and the rocker. Rotating the rod, it should just barely drag. My method is to alternately rock the rocker against the valve tip and push rod while pulling upwards with a hand on each side of the rocker's body. I find it pretty straight forward to feel when there's no gap. Doing it this way might not be far enough, but adding 3/4 turn preload on the nut will more than compensate for that. (BTW, GM recommended 1-full turn to preload.)

 

I just spent some time learning this and it took me a bit to acquire the feel. One thing that helped me: ditch the ratchet and use a small breaker bar. Reading your post makes me think you were standing there next to me

 

Aha! Look what I found digging through my scrap pile here. The 350 timing marker vs the 400 marker. The 400 was in a van chassis. Chevy must have moved the marking at 12 o’clock on this engine. As it is nearly impossible to get a side reading in a van chassis. The engine is buried pretty deep in the dog house.

That addresses some head scratching. Learning as we go here. Solving previous unknowns.

 

Exactly. Now you can add a new bolt-on timing tab that works better for a car application and add a new zero mark on the balancer. Probably need to get the TDC tool first but at least you are out of the woods now.

 

Here is a better shot. My dots are aligned properly.

 

Use whatever timing tab you think you will stick with. Around 2 o'clock seems to work best, usually, except maybe on vans LOL.
After you get the piston stop tool, mark the balancer about 2" away from TDC,
tighten the piston stop until it touches, recheck, then rotate engine the other way and make a 2nd mark.
True TDC is exactly halfway between those two marks. Make that a permanent mark.
Then set the engine to true TDC. using that mark.

Even an OEM setup can be 1-2* off.

I will bet that solves your distributor alignment issue.
I'll bet it points directly at one tower now.
Make that one #1.

Various stock SBC timing mark locations:
12 o'clock, 1 o'clock, 2 o'clock.

Only the 68 version lines up with the keyway and the bolt hole on the balancer.

The two covers you showed look to be the 30* apart versions. That would really retard your timing!

 

Something that belatedly occurred to me. TDC is what it is but it's not unusual to stab in a distributor at somewhere other than TDC. I stuck mine in @ 12 degrees BTDC. I also got one of those cheap timing tape sheets to ensure that the marks on the tab are actually correct for the size balancer in use.

Also, careful with the piston stop as it can leave a small mark or dig in your piston. Ask me how I know
Not enough to matter but careful. It's definitely easier to roll the engine by hand with the plugs out, if you use the metal stop that might not be a bad idea.

 

Folks all your points make sense. I have been researching and learning. Following sound advice. Yet things weren’t adding up. I had feeling my valve timing was out. I even mentioned valve timing in the title of this thread. The unknown truth smacked in the face at 4 am this morning, in bed.

I bought a bolt-on timing mark indicator. It bolted to the 2 o’clock position as per the image above. The 350 and the 400 internally are mostly the same engine, except bore and stroke, externally balanced and steam holes right? Not quite so. An important little thing was overlooked. The crankshaft key-way in the 400 when used in a van application is indexed so the timing can be read from 12 o’clock. Straight above the pulleys. Not knowing this, I time’d the engine with the timing marks lined up at 2 o’clock. I lined up my timing chain and gears at this position, truly believing #1 was at TDC. I now realize my valve timing chain is out. I have to go back in there and address it. I set all my push rod clearances at this same incorrect timing mark. I will go back in and address all.

Lesson learned.