A roller timing chain can be used on flat tappet cams. Roller chains are bicycle type chains that have been commonly used on engines forever it seems. The notoriously failure prone timing chains were the laminated link type that were mounted on plastic timing gears. Ford V-8s used the laminated type for many years but sometime in the 90s they went to the roller chain. All overhead cam timing chains are roller chains.
Man this post has been confusion. Stock then 408 now back to stock. I’m going with the theory that the stock motor is back in.
I agree with your assessment here. This happened to me about 12 years ago about the time they changed the oil formula from SL to SM and they removed the zinc and phosphorus. I ended up mushrooming two lobes on a new cam/lifter. My problem was I was backfiring through the carb and exhaust and couldn’t get the engine to run even at higher rpm. His problem is backfire through the carb so it would indicate that the exhaust valve is not fully opening to release the gases and they are escaping into the intake when the intake valve opens. Most people don’t know that those lifters spin and they essential wear into the cam. If you swap the cam, you always have to replace lifters. When you replace the lifters, there is also higher risk that the new lifter and old cam will not breakin properly together. If you clean your pushrods off near the rocker and use a paint pen and draw a vertical line on them you should see them spin around when the engine is running.
It also sounds like there was a problem before timing swap and all the other work that has been done. Sounds like he has been changing a lot of good parts searching for the problem but still has not found it.
If he uses a laser heat gun, he can measure the temperature at each exhaust port. Under this theory that he has a cam issue, he will find the cold(er) exhaust port that will isolate the issue.
Another possibility is a carbon built up on a valve not allowing it to fully close. Could have a valve guide coming loose and not allowing a valve to fully open.
Yes it is confusing but you are correct, stock engine is back in car. I have wondered about the cam wiping a lobe for a long time now. I didn’t know about the thermometer trick but I will look into it. I appreciate all the feedback and apologize for my long response times but I am reading every post. I plan to try the propane this evening. My next plan of action will be infrared thermo. I will update when I have the results. Thanks Again for all your help.
What if you got a cheap dial indicator, pulled the valve covers, and measured the lift at each valve as you turned over the motor by hand? Here’s one for $26, magnetic base included:
Or $30 for a clamping one from HF:
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Also if you have a chewed up cam, you should see it in the oil pan. If you got a week or two to wait, you could drain your oil and catch a sample and send it off. I historically used Caterpillar SOS program. https://www.cat.com/en_US/support/maintenance/sos-services.html
If you got flakes in your oil, I would recommend a complete dismantle of the engine. I would assume that the original engine is quite valuable to the car and saving it should be high priority to maintain high resale value of this car. Having a replacement engine on this car can significantly deduct from the value of the car. Easily $10K but maybe as high as $20K. # matching matters to people who are paying big bucks.
Yes your right. The engine is priceless to this car. Just did propane test. Nothing? At this stage I just want to find something wrong! I will get a thermometer and do a Google search. Just baffles me that she runs very nice until she warms up and then cough, cough??
Can you describe the blow back another way?
Do a compression test, I’m thinking worn cam or weak valve springs or burnt valve .
I really wish I could. I suppose its technically a backfire but there us no pop. It’s a cough causing engine to stumble and there is noticeable gas released from both primaries. Again, only when engine e warms up after a minute or 2. I wonder if I could post a video?
It ran fine when removed 5 years ago and you recently reinstalled the engine. Did you do anything to the engine prior to reinstalling it? New plugs, tune up, and wires?
Just to be clear, this problem existed before swapping lifters, timing, fuel pumps, distributor, plugs, wires, etc? You have swapped all those things and it is still having the same issue?
It runs fine above 1400 rpm but stumbles and sputters and blows back out the carb at low speeds? At higher RPM, your distributor will advance the timing via vacuum or mechanical spring and weights. At higher RPM the timing is changing from the 6* BTDC that you have at idle. Have you tried advancing and retarding your timing? No need to use a timing light, just lightly loosen the distributor clamp, start the vehicle and slowly turn the distributor left and right to see if it runs better at idle. Does it run fine under load at higher rpm or is your assessment only in park with no load?
You are clear on all areas. Everything you listed are items I’ve done to try and solve problem. Distributor is loose, easy to turn. Vacuum line is d/c and plugged. Seems to run worse when vacuum is attached
Ok, I think I understand, thanks for the explanation. OP changed to a new timing chain and timing gears, but left everything else on the engine stock. I’ve always thought all timing chains used in car engines for the last 50 years were the roller type.
I’m more familiar with hi-vo timing chains:
900rpm is a fast idle. How does it behave at normal idle (~650 I’m guessing)?
Is the cough at a consistent pace, like old faithful, or kind of random?
Sometimes there is no way to solve the problem other than to go down to the bare block and start over using known compatible components.
This thread is rather long so let me beging by saying that I did not read it in its entirety but read enough I believe. So please excuse me if I repeat a suggestion that has been made prior.
Is it possible that you have a rocker tightened too tight with a zero tolerance? If so…as the engine heats up the pushrods and lifters expand…that could add up to actually floating an intake valve just slightly…just enough so that it is opening prematurely ? The theory definitely holds water, I am just not certain it actually applies to your situation currently…something to check perhaps.
You could even induce excess valve lash just so that the rockers can be heard clicking away… does the issue go away? Its a rudimentary and simple test to try just for giggles. If the excess lash you induce stops the issue, then you can figure the rest out from there. You could also measure each of your push rods and really look closely at the rocker arms as well as the tops of each valve to see if you can spot any anomaly in the valve train components. Hell you could possibly have one lifter that is solid instead of hydraulic that somehow got mixed up in the ingredients… the excess lash experiment will suss out many components that could be the culprit.
Its just a thought and easy to do the experiment. You really have nothing to lose by trying it out.
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650rpm is worse. More random I would say.
I reread this thread and it appears that the engine has roller lifters installed on a conventional camshaft and if so that is the most likely cause of these problems.
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I couldn’t find anywhere he said it had roller lifters. He put on a roller timing chain.
Sounds like a vacuum leak to me.
Have you pinched or capped off the brake booster as a test?