235 popping thru carborator under load.

[jeffbcn]

Sorry if this is a long read but I need some advice.
I have a 47 thriftmaster with a 235 from 1962 and heads from a 261 1955 thru 1957 according to the casting numbers.
I have no idea about prior service. I have had it less than a year and put about 2500 miles on it. A couple of weeks ago I noticed intermittent popping thru carborator. I just took it on a 700 mile round round trip and when I came back the popping was more pronounced. if I ease it up to 2000 rpm it sounds great. Any higher or under load it pops and loses power. I ran motor flush and changed the oil. I timed it, new Dragonfire hei distributor. Still pops.
Opened the valve cover and it was dry, even some surface rust on rocker arms.i ordered new oil pump.

My question is this, can I just replace the oil pump, do I have to rebuild the heads or is the whole engine toast?

Any suggestions are welcome.

[Nordic]

Sounds like an intake valve is sticking

[joedoh]

intake vacuum leak. big one. see if the bolts holding the carb are loose, its usually at the carb base

[Jemezcrusher]

I agree with Nordic, but seems weird that it is intermittent. If your valve train is dry-ish the stems and such may not be getting proper lubrication at rpm and things are getting too warm and expanding, causing a valve to hang up

[Softpatch]

I could go either way stick intake valve or massive vacumm leak
try 4oz of marvel mystery oil in the crankcase (lubeoil)
And another 4oz per tank full (15gals)
for a few 100 miles........
You would be surprised what it will do...Sp

[jeffbcn]

Found carborator loose by a half turn. As I was tightening it I noticed a bolt below the exhaust manifold sticking out. Upon further inspection I found on bolt missing and the other almost out. It's the location where intake and exhaust manifold bolt together. Put new bolts with lockwasher and blue locktite. Was so excited but no go. Still pops. I also added a bottle of Seaford. Maybe I should drive it easy for a bit to see if it helps.

[joedoh]

Originally Posted by jeffbcn

Found carborator loose by a half turn. As I was tightening it I noticed a bolt below the exhaust manifold sticking out. Upon further inspection I found on bolt missing and the other almost out. It's the location where intake and exhaust manifold bolt together. Put new bolts with lockwasher and blue locktite. Was so excited but no go. Still pops. I also added a bottle of Seaford. Maybe I should drive it easy for a bit to see if it helps.

if it was running lean, your plugs are probably fouled. clean them up, costs nothing but the time, and you can look for any other problems with them out.

[jeffbcn]

I changed the plugs when I changed my oil just a couple days ago.

[joedoh]

did any of the old ones like whitish, like running lean?

[jeffbcn]

Light brown except #5&6 both looked a little darker and a little tapered. I was running platinum plugs gapped at .050 because of the Dragonfire hei. I went back to the plugs called for gapped at .035. no difference

[joedoh]

Originally Posted by jeffbcn

Light brown except #5&6 both looked a little darker and a little tapered. I was running platinum plugs gapped at .050 because of the Dragonfire hei. I went back to the plugs called for gapped at .035. no difference

then I agree with the others, you are not likely looking at a vacuum leak.

[Second Series]

I have a similar issue with my 47 thriftmaster with 54 235. My 235 has hydraulic lifters and I suspect one may be partially collapsed. It had a bit of rattle so I took it to a shop and had the valves adjusted. That's when the popping started. I Think that when it gets good and hot the one collapsed lifter expands and prevents a valve from seating. Fifteen years ago I had this engine installed by a mechanic way out in the boonies, south of Lockhart Tx. He said the lifters were bad, but he didn't want to drive to town for replacements. I drove it like that for a decade and forgot what he told me when I took it for adjustment.

[jbarron]

You might try checking the timing on #1 and #6 to see if your timing chain slipped.

[dwcsr]

I'm going to suggest you fix your oiling issue with the rockers, If your rusty on top your running dry and the valves ad rockers may be hanging and not able to close at high speeds. Specifically look at rockers that have dark plugs. Running out of fuel at high speed will cause popping as well.

[Speedbumpauto]

Take the valve cover back off and look carefully for a broken valve spring, probably intake. At low rpm's even the broken spring can keep up but at any higher rpm, the valve hangs open slightly during combustion and it pops back through the carb. Could also be a severely galled rocker arm holding things open if there is a serious lack of oil.

[tmoble]

Don't run Platinum or other fancy plugs in these trucks. take them out, throw them away. put in the regular gasketed 13/16" hex plugs.

Those Pt plugs are good for modern cars with EFI and multi-coil ignitions. Old trucks? Not so much.

[jeffbcn]

I put in a new oil pump, pickup tube and made sure the delivery tube was clean too.
I am now getting some oil to top of rockers. It's more of a weep between rockers not a squirt. Enough oil to pool and drain back to pan. The oil coming out is black and gritty not like the fresh oil in the pan. Before dropping pan I ran motor flush for 5 minutes and put Seafoam in with new oil.
Now I wonder if my rocker tube was completely clogged. Also the engine is from 1962 so it's supposed to be full pressure with hydrolic lifters. Could they be clogged too?
I took it on a 10 miles run today and some of the popping decreased.
Am I on the right track? How much oil should the top of head get?

[Coupeguy2001]

What is your oil pressure at idle, and again at 40 in high gear?
If you are getting gritty oil, you are ruining the rocker shaft by not taking it apart and cleaning it.
You might put some regulated compressed air through the oil tube to clean it out. You can use pipe cleaners too, or engine oil chamber wire brushes, but they are very long.

plugs are plugs, except that the newer plugs have a resistor in them for protecting the quality of your sound on the radio. Your ignition should produce about 35,000 volts to fire any plug, even the ones with resistors in them.
I would double check the plug wires though, and see if you have resistor wire. double resistors may be too much for your coil.
If you want to keep your setup, i would change the coil to a high performance one, and check the engine to frame ground cable and make sure the ground points are clean.

You might want to back off the intake valve adjustment .002. sounds like whoever adjusted the valves may have gotten them a tad tight.

If your now oiling, and you think it is adequate to keep the rocker shaft lubricated, I would do a another oil change in about 500 miles, and use a synthetic blend oil.
Using straight synthetic oil in an engine not made for it may affect your seals. Other than that, it's the clearances that may affect the oil pressure.

Adjusting the valves is easy. get yourself tha 9/16 wrench that has thin wall box, and a flat tipped screwdriver that is fairly square. Purchase a feeler gauge set, and make sure that there are not more than two gauges put together to make your lash thickness.
then take the rocker cover off, and warm it up, watching the rockers, and seeing that the pushrods rotate, or are easily rotated while the engine is running. check your oil pressure while it is cold, then after it warms up. there could be as much as 20 pounds difference between hot and cold.
Then while the engine is running,try to get the feeler gauge in between the rocker and the valve. If it is the right thickness gap, the feeler gauge will slide in under the rocker, but it might not go easy. If it is too easy, the lash is too great.
If the gauge slides in easy, you need to loosen the nut, and turn the center screw until the feeler gauge drags between the valve and the rocker. then tighten the nut. recheck your gap with the gauge again. You might have to do each valve a couple times to get it right.
If you do it with the engine shut off, the lifter may bleed down a little bit, and you end up with too tight of a gap, and your valve could hang open a thousandth or two, and give you the popping.
If you are more comfortable adjusting with the engine off, try shutting off the engine, and holding the screw with the screwdriver, back off the nut, holding the screw from turning. If you have to increase the gap, don't back off the screw more than twice the thickness of the screwdriver blade, then tighten the nut, and recheck the gap. lessening the gap is the same procedure, but only tightening the screw the thickness of the screwdriver single blade thickness. If your valve aren't noisy, they are probably too tight, or right on.


Also, what oil are you running now?
Cam manufacturers have been warning for years that the cams will go flat on flat tappet cams because they have taken the phosphorus and zinc out of the oil for the EPA.
It seems that the phosphorus and zinc on high mileage engines is getting stuck in the catalytic converters, so they just took it out.
older engines suffer the consequences unless you change the oil you use.
Phosphorus and zinc as a combination make an extreme pressure lube , that in the oil, protects the camshaft from wear. without it, your cam will go flat.
The options are to use oil made for diesel engines, and you can use a 15-40 weight oil, or use the synthetic blend oil.
For my 57, I use straight synthetic, but it is an 89 corvette 350, and for my wife's car, I use synthetic blend oil, and add an extra full synthetic quart to get to the fill line on the dipstick.

At this point, I would do a compression check , one when the engine is cold, and one when it is hot. Compare the two numbers, and make sure the numbers don't change by more than 10%.
If the numbers on any cylinder change appreciable between cold and hot, you have a binding/sticking issue that is altered by heat.
Remember, on cold compression checks that the engine is made to run warmed up, and that the cold numberss might be a little low, because nothing is expanded yet.

[jeffbcn]

Thank you for your detailed reply. At this point it looks like I need to pull the rocker Assy. out and clean it.
I don't have an oil pressure Guage. Reproduction gauges were for the original 216 and max out at 30. Gonna have to get one I guess.
How much oil should get into top of head?

[tsmith8]

is your engine pre-detonating? What is the compression of your engine and are you running regular gas?

Check your plugs to see what they look like and add an octane booster to your tank.

[jeffbcn]

Compression test 6 months ago was 150 on all 6. Normally I run 87 octain gas. This time I put in 5 gal. Of 91 and 2 gal of 100 octain racing fuel just to see what happened. No change. I did take it on a 10 miles freeway run and some of the popping lessened a little. Still not much power. 2500 rpm max on slight incline barely 3000 downhill.
I can move pushrods up and down almost 1/8th inch on some when not running. Gonna pop distributor cap off Dragonfire hei just to look inside.
Looks like I need to clean out rocker tube and adjust valves.
What about hydrolic lifters? Could some be plugged and not opening enough for valves to work properly? I don't know where the get oil from. I do know the cam was covered in oil because when I changed the oil pump I could see it. Dripped all over me.
Am I on the right track or is maybe my cam flattened?

[Coupeguy2001]

If your engine is popping back through the carb, it is an indication that your cylinder compression is not staying in the cylinder, but going past the valve, and back up into the carb. That's why I thought you might have a intake valve slightly open.
The reason the race gas does get the popping lower is because the fuel is now waiting for the ignition system to fire it instead of the deposits in your cylinders to get the cheap gas of today to light it off. I don't think you need more than the 87 or 91 of today's gas to get your buggy running.
If you back off the intakes just a couple thousandths of an inch, and the popping stops, that is what you want.
But to be on the safe side, adjust them all.If there is grit coming out of the rocker shafts, the oil is carrying particles that is not good for the metal surfaces that are rubbing together. If you see the spring on the rocker shaft, it is supposed to keep the rockers from sliding on the shaft. if you loosen the rockers, and slide the rockers to where you can see the bottom of where they are normally riding, you can gauge with your fingernail just how worn the shaft is. Not an easy task, but doable before you tear it apart.
If you use a depth micrometer, or a dial indicator on each rocker, you can determine if your cam is worn.

[Coupeguy2001]

You know, we forgot the most important thing.....drag out a timing light and determine the engine is timed properly!

Check your cam lobes for lift,and put the oil in it if they are not worn.

[jeffbcn]

Timing was spot on.

[jeffbcn]

I solved 95% of my popping issue. I had replaced the fuel pump and lines and put on a new carborator to no avail.
So I decided to adjust the valves. This motor came out of a 62 chevy truck so it has solid lifters. I found several valves that must have had an 1/8th inch gap and a couple with no gap. Adjusted all to either .020 or .008 per specs. Truck runs so much better. Getting oil to top now. Had to put a K&N air cleaner because my oil bath would not fit on new carborator. Need to time it and adjust carborator again but the popping is 95% gone and engine power is restored.
How the valves got so far off I have no idea.
Thank you all who took the time to respond and point me in the right direction.