The Stovebolt Site Forums The Shop Area Engine Shop Adjusted Valves, Started backfiring?????

When I first bought my 52 AD with a 58 235 it seamed a little noisy. I adjusted the valves with feeler gauges to the proper settings. The truck started running warmer than usual and someone on here siad the valves were probably too tight. I readjusted the vlaves and loosend them up a bit, still within spec. Well I was taking the truck in to have the tranny converted to an 700R4 and while I was driving along the truck started backfiring slightly but I kept going wanting to make it to the shop. It got worse and worse. The guy at the shop says it is my carb but the shop foreman just called and he said he thinks its internal. I thought it was points but why did this start after I adjusted the valves? I asked the foreman to take the valve cover of and look to see if I left a retaining nut loose and a rocker came loose. I am at a loss right now. Any suggestions?

The carb did look wet when we got to the shop.

Rcimp,

I'm a pretty firm believer in the cause & effect theory. If you had the intakes way too tight you could be blowing air/fuel back through the carburetor which would make it damp with fuel...and cause backfiring.

I would make sure the shop ran the valves to the proper settings before they did anything else. If that didn't do the trick then it would be time to start looking around.

Stuart

I readjusted the valves and loosened them up compared to where I had previously adjusted them. I know for sure they are not too tight right now, unless they tightned up when driving? Is that possible?

Rcimp,

If you loosened them up then they are loose and wouldn't get tight by themselves. I don't think 'too loose' would cause anything other than poor performance.

Could you have knocked any plug wires off or done anything else while doing the valves. Could a pushrod have slipped off a lifter. If everything was fine before running the valves then it seems the problem would be something associated with that chore.

Improper valve lash shouldn't make the engine run warmer. Excess advance timing can result in higher operating temperatures and could account for backfiring. A fuel mist coating the carburetor sure sounds like tight valves though.

Stuart

One theory is, if an exhaust valve is too loose or the retaining nut came loose and allowed the exhaust valve to loosen up then it may not be opening enough not allowing the gases to exhaust out causing the backfire when the intake valve opens which in turn will cause the fuel mist around the carb. What do you think?

I also think points can cause this to.

The truck was running fine for about 5 or 6 miles then all this started happening.

I think Stuart is on the right track with the cause/effect theory. The fact that it ran fine for a few miles then started acting up brings a couple of questions to mind:

When you adjusted the valves, the engine was HOT, right? Did you use the static adjust method or adjust them while the engine was running? And then a really basic question, is your '58 a solid lifter motor or hydraulic????

I adjusted the valves with the motor hot, static and I thought all the lifters on the 58's were solid? My 235 does have 30lbs of oil pressure when driving.

If a valve adjustment came loose you would get a loud ticking noise. It would be fairly obvious. I would look at the points. If there is no lube on the breaker cam it can wear the rubbing block to where the points are barely breaking.

Rcimp,

That's an interesting theory about the exhaust valve. How true it is I have no idea. I don't think the intake valve would start to open until the piston was past TDC a few degrees. If the exhaust valve were set too loose, it would probably only be by a few thousandths at the most and it doesn't seem like, coupled with the fact the piston was now on a downward stroke, that there would be much 'backwash' into the intake and up into the carburetor....whew, what a long sentence!

But who knows, maybe so. I looked at some of your previous posts and there seems to be a string of problems and unanswered questions on your rig. Some heating issues and a few valve adjustment questions.

If all the tune-up parameters could be met, valves perfect, timing right on, carburetor tuned and functioning then there would be a benchmark to go from.

If the truck is in the shop right now, the mechanics are qualified (for a old bolt engine) and the hourly labor rate isn't astronomical, it might behoove you to have them figure out exactly what is wrong. Good luck

All 1958 truck 235s had mechanical lifters but all passenger car 235s had hydraulic lifters.

Also, I think that from 1958 onwards the truck 235 block was set up to work with hydraulic lifters - it could have been converted.

I guess the only way to know for sure if it is hydraulic lifters is to pull the side cover off?

As far as previous overheating problems, I tested the water temp with an A/C temp gauge in the radiator and the water at its hottest point was 196* idling for about an hour in one place. My dash gauge was saying 212* so I faulted my gauge. The truck never acted hot other than the reading on the gauge. I asked for a 180* thermostat from the auto parts store but I guess they could have had a 195* in a 180* box???

I have not tuned this truck since I bought it so I should get that done first. Should I rebuild the carb myself or buy a rebuilt? Does anyone know a good rebuilder at a reasonable price?

The shop the truck is at is a custom rod shop, they are installing a 54-59 rearend and a 700R4 with a new steering column. They don't do engine work, funny huh?

It is certainly possible for valves to tighten up on their own as well, from one of two mechanisms:

The pushrods in a 235 rotate because the cam lobes are off center and it makes the lifters rotate. This is a clockwise rotation which is the same direction the adjusters rotate to tighten. If there is enough friction between the pushrod and the adjuster, and you didn't tighten the locknut, it is possible that the pushrod rotated the adjuster.

The other mechanism is that the valves got too hot and the seats receded into the head from overheating. This is a runaway condition because it tightens the clearance.

Either way, readjusting the valves fixes it unless the seats got ruined and leaky from overheating.

If the truck sat for a while the carb could start leaking independant from the valve problem, but a tuneup always starts with a valve adjustment, since a problem there will mask any carb or ignition problem.

Before you let them do a teardown, insist on a full diagnosis and an estimate to repair what they think is wrong. I'm getting a very uncomfortable feeling about this shop's approach to the problem. Before I'd allow anything else to be done, other than the original transmission swap, I'd want some sort of assurance they're not just on a fishing expedition for a bigger payoff.

At the very least, I'd want to see the results of a compression test, and a cylinder leakdown check. Also get them to check the dwell and ignition timing, and possibly redo the valve adjustment. If there is something going wrong internally, one or both of those mechanical tests should show some incorrect readings. If they aren't willing to do those things, or don't know how, call a tow truck and get your vehicle out of there, pronto!
Jerry

I am curious about how they are going to hook up the Throttle Control Valve cable to the Carburetor when they install the 700R4
I realize this is getting off the original topic.
Cleon

This shop does not do motor work. They will install your motor or do conversions, and custom machine work.

I have purchased a new set of points, condensor, and coil. I will go to the shop and install them and re-adjust the valves. If it is something internal it looks like I might just have to install a V8 Already got my eye on a nice little 327.

As far as the TV cable, I am sure they will fab up some little bracket, they have a full machine shop.

I just called the shop to inform them that I was coming in to do a tune-up on it and the shop foreman told me he took off the valve cover and one of the retaining nuts on an exhaust valve had backed off. He adjusted the valve cold to the same as another cold valve and he said that cured the problem. I am still going to go and do the tune-up and re-adjust(or make sure) everything is in spec. My theory stated on page 1 turned out to be right. I am glad it was something easy. It was my fault.

Rcimp,

Great news. You proposed a theory and the facts substantiated it. This will certainly go into my little book of knowledge, thanks.

Stuart