The Stovebolt Site Forums The Shop Area Engine Shop Rough running - diagnosis

Plugs, points, and wires have all been done. Condenser not yet. Will do some spark checking this weekend.

Timing has been set to ball. Can't run long enough to do anything better than that.

(To Deve's questions) -- fuel system is new -- tank, pump, and lines.

A question was asked about the "power valve". The "power activating piston" and its function are described here: http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0659.htm
The piston can be cleaned and polished with some very fine sand paper(600-1000 grit) and a hand drill. chuck the long skinny part into the drill, polish the piston part until you have a smooth fit in the body of the carburetor. It must be smooth and free, all that moves it is vacuum and a spring. Usually only moves at full throttle under a load. But it can move under partial throttle and loading as vacuum demands. If it starts and runs most adjustments can be made. Even with a poor missing idle you should see a Dwell angle of about 30 degrees. That confirms the point gap is correct(0.0018 to 0.0022 inch). More "Specs" here: http://www.tpocr.com/chevr.html
The stuck heat riser must be fixed. So do that first. After that is working start with the suggestions as posted above. Lots of smart willing folks here to help you. Keep us posted.

Just a note for some more on the heat riser issue: https://www.stovebolt.com/ubbthread...al_spring_on_heat_riser.html#Post1121720
Discussion is current and may prove to be helpful.

Might have had a modest breakthrough.

Did a complete spark check. Coil to distributor wire. Spark at all plugs, for some reason #3 and #6 seemed a hair weaker for whatever reason. Put a new terminal on the coil-to-points wire. Had a questionable connection there.

Startup - same symptoms

Replaced condenser. That turned out to be an adventure. An oversized screw had been installed and head was nearly stripped. Didn't know it was oversize until I reinstalled. Had to reuse it.

Startup - same symptoms.

Loosened distributor clamp (another struggle) and advanced the timing to fire so the ball was just outside the left of window.

Startup - engine runs completely different. In a good way. Smoother. Was able to push in choke cable nearly all the way. Guess the timing was just retarded way too much.

Heat riser still stuck. Try that another day.

Got a good, long run yesterday with the help of buddy. Got engine fully warmed and the choke all the way in for several minutes.

The aforementioned advance of my distributor made a big difference. But now I can do no more advancing. The grease cup is hitting the vac advance. Is pulling the distributor to re-align everything the only way to remedy this? I think I have an old thread tagged with a procedure somewhere.

Exhaust heat riser still stuck. Need to try that one more time and if I can't... punt and switch out manifolds.

Idle was a little tougher than I'd like. But without exhaust hooked up or being able to fine tune the timing...also a little tough to tell.

what does the old thread say to do?

I've seen Deve and maybe a couple other folks describe getting #1 in just the right position and getting the vac advance set parallel to the block. My advance is roughly 5 o clock to the block.

Didn't know if there was an easier remedy to my situation. Assume that pulling dizzy is in order.

In other news, pulled the manifolds off and tried/failed to free heat riser one last time. Used a few different cycles of heat and PB blaster. Guess I've no choice but to rob the manifold from my parts motor.

If you have any concern that maybe good oil is not getting to the rockers, or just want to check that, it would be a good time when the distributor is removed to prime the oil pump. It IS a good time to pull it and put it in the right place.

Dads50 has a nice video on how to pull and reinstall the distributor as I recall. Be sure to get it all the way down when putting it back. Check oil pressure right away on restart.

Lots of us here to help you get it done.

You shouldn't have to remove the distributor

Put pointer ball

loosen the clamp on the back. Turn the body, reindex the wires

I'm an idiot. Knew I was missing something easy.

Me too. But I am even worse, I didn't think I was even missing something easy! Although, pulling the distributor is something I do a lot.

Going to swap to a manifold set with working heat valve.

Understand a few things reading old threads. But also some questions.

1) check for warpage with straight edge
2) connect intake to exhaust only loosely until snug to block
3) install gaskets on block --- no special goop?
3.5) any sort of anti-seize on the bolts?
4) tighten in shop manual sequence. I don't see any way to get a torque wrench on some of those bolts?
5) tighten intake to exhaust connection

No goop on the gaskets, always a good idea to use anti-seize but not sure how necessary it is due to the extreme heat. And you have it right. If you see any warpage, the machine shop will re-deck the surfaces for about $60 or so. Its a really good idea to have a flat surface there. If you do that, bolt it together on the engine as you describe, tighten down the intake to the exhaust, but when you take it off to have it surfaced leave the intake and exhaust tight to each other, then take the whole thing to the machine shop. Don't forget about the three alignment rings.

How critical is the torque setting? Other than the outside two bolts, there's no way to get a torque wrench on them. Guess maybe I can "feel" the outside two and then try to replicate the middle.

Need a little metallurgy lesson. My "new" manifold had a different size port for the wiper vacuum. Need to hit the hardware store for an adapter. Will brass be compatible with the cast iron?

Yes, it would be OK to " "feel" the outside two and then try to replicate the middle"

brass is OK - use the anti-sieze here, if you want to do so

If you want to see what NPT size you need for your manifold, this may be of help.

http://devestechnet.com/Services/PCVUpgrade

(only offered for the three pics on NPT sizing.)

Bumping an old thread. How much warpage of the manifold surfaces is too much?

I've got a manifold pair with a working heat valve that will replace the one with a stuck valve. If I turn it over, and lay a framing square across it, I can see maybe 1/32" (eyeball test) of daylight on a couple of the exhaust surfaces.

My theory is that minor gap should close up once I loosen the two manifolds from one another and torque it up to the head. Between a little bit of flex in the manifold and the gasket thickness...that I might be OK without getting them belt sanded.

What do you all think? Worth trying it as is, or need to have the surfaces milled a bit?

Why don't you loosen them now on the bench and see if you can move the two faces into alignment.

You can also install just the manifold in question to the head with no gasket and see if when you torque the bolts it removes the bowing. You can verify by trying to insert a thin feeler gage between the head surface and the manifold. If you can stick anything thicker than a .005"-.010" feeler gage between them, then that should confirm your analogy.

Good suggestions. Thanks.