Rebuilt Engine Issues

[Craig French]

I rebuilt an engine with new sleeves, pistons, rings, valves, babbitt, and other new parts. I put it on my test stand and got it running just fine. It has only run about a half hour with no issues. My last test was to short out each plug to see if the engine speed slows down. Nothing changed on plugs one and two. Plugs three and four had a marked reduction. The engine ignition was stock with Anderson timer and wood coils. I switched plugs one and three and the plug in one still didn't change speed. I then switched coils for one and three and the same thing happened, NOTHING. I have another T with the VW distributor and modern coil. I tested that engine in the other car and each plug shorted out with a reduction in speed. So I installed the VW distributor and coil with all the wiring into the engine on the test stand. The same thing happed with the so called modern ignition. Plugs one and two indicate spark with the screw driver shorting to the nearest head bolt but the speed didn't reduce. Shorting plugs three and four did reduce the engine speed. All cylinders have similar compression, about 90 PSI. The engine runs like a normal Model T engine. I can't figure out why two cylinders don't act like they should with shorting out the plugs. I have no idea why this is happening. Does anybody have an idea as to how to fix this condition? Please let me know. I would not be happy if I installed the engine into the car and then found out that there is a power reduction due to the weakened cylinders number one and two. It is much easier to fix the engine while it is on the test stand. Please let me know if you have any ideas.

[Jerry VanOoteghem]

I'd let it run in a bit more before making any conclusions. Allow the rings to seat in at least. Maybe check the gaskets on your intake too?

[Scott_Conger]

Maybe check the gaskets on your intake too

this is precisely what I would do, too.

[Les Schubert]

Does it sound like it’s hitting on all 4 cylinders?
Pull the valve cover and examine the valve action, are the the valves actually opening?

[Les Schubert]

Does it sound like it’s hitting on all 4 cylinders?
Pull the valve cover and examine the valve action, are the the valves actually opening?

[browning]

Any chance of a tight valve guide in cyl one and two. Good time for a compression test.

[Craig French]

Thanks for the ideas. I will check the intake manifold gaskets. I don't think the valves are an issue since I get all four cylinders showing the same compression, 90-92 PSI. The compression tests should resolve any issues with the rings and valves. Any other ideas? I appreciate all your advise.
Thanks
Craig

[TXGOAT2]

In addition to the above: Valves that are tight in the guides may cause issues when running, yet still allow a good compression check. I'd also check valve to lifter clearance very carefully. Too little clearance, especially at exhaust valves, could cause poor seating while running, and yet still show a good compression check profile. Check head torque. I assume you're running the engine with coolant and 20W oil.

[Norman Kling]

A compression test will tell you if the valves, rings and head gasket are good on those two cylinders. If you have approximately the same compression around 50 psi on all cylinders, your engine is most likely OK. And you have already swapped coils and found it doesn't change which cylinders are misfiring. Next thing to check is the vacuum in the intake manifold. Try turning the mixture rod counterclockwise and see if the first two cylinders begin to run smoother, but maybe the last two become a bit rough. That might indicate a leak in the gasket at the front port. Sometimes the manifold gasket allows some extra air to get into those two cylinders.
Let the engine get up to operating temperature and adjust both fuel mixture and spark to see it will smooth out.
Your case can have one or more causes, so you might need to keep working on it until you find out what is causing the problem. Sometimes it can even be an ignition problem. Be sure all the wires to the timer are in proper order and the contacts in the timer are clean and operating well. Sometimes the problem can even be caused by coils not sparking at the correct timing causing one or more to fire late.
Norm

[jab35]

Craig's original post: " All cylinders have similar compression, about 90 PSI."

Norm: " If you have approximately the same compression around 50 psi on all cylinders, your engine is most likely OK"

Clearly, your compression ratio is nearly double what it should be! Good luck solving the mystery, and seriously, don't try to reduce the CR.

[TRZim]

I had the same identical problem, checked everything. Finally out of frustration I changed timer for the third time but this time I replace all the ignition wires on the firewall. That solved the problem for me.

[TXGOAT2]

What type is the ignition system? Is the coil box in top condition?

[Craig French]

Thanks for all the suggestions. I will check out the valve movements and other intake manifold concerns today. As noted in the comments, my compression is over 90 PSI on all cylinders. So something is working right in the valve train. Also, please note that I've used two complete different ignition systems on this engine. The first one was a stock Anderson timer with original wood coils. I removed that entire system and installed a working VW distributor with a single modern 12 volt coil and all different wires associated with that system. The results were identical to to original system, no change in the firing on cylinders one and two. Also please note when I rebuild the engine, I removed the mag coil ring since some coils were broken. I also removed the magnets from the flywheel since I plan to run the car using the battery only (12 volt). The commonality for these two cylinders to not indicate much power is the intake manifold since both cylinders one and two are connected by that manifold. I will continue to check out the engine today and see what I can find. If anybody else has some additional ideas, please let me know.

Thanks,
Craig French

[TXGOAT2]

An intake valve that is not fully seating at operating speeds could affect the other cylinder on the same manifold branch. It would have an effect similar to a manifold leak.

[Adam]

If it is anything at all; Whatever it is probably won’t require removal of the engine to fix. Install the engine and see how it actually performs in the vehicle. It usually takes me 3 hours to remove a T engine and 6 hours to install. That time covers EVERYTHING (radiator, steering column, radiator, sills, hood, etc). You very well may pass the 6 and 9 hour marks troubleshooting on your test stand and not find anything wrong.

My best guess would be that your front intake port is a little leaky and the front cylinders are working well enough to not be dead misses running but not as noticeable as the rears when shorted out. This might be combined with a leaky throttle shaft on your carburetor which is also an intake leak under high vacuum for the whole system that would throw all cylinders lean at high vacuum (which would be idle or high idle). Only other thing that could be possible is that you have a very poor quality used cam. Was a new one installed? Sometimes wear is much heavier on the front lobes & if the valves weren’t timed by piston position there could be a noticeable unbalance in performance between cylinders but your compression test wont show it.

[Norman Kling]

You must have a high compression head because it is much higher compression than usual. What kind of manifold gaskets are you using? Do you have the gland between the block and manifold? If you are just using flat gaskets without glands, you could have a misalignment of the manifold. You might try some spray such as WD 40 around the intake manifold to block connection and see if it changes things. Also one more thing to check would be to try changing the gap on the spark plugs. It takes a stronger spark to jump the gap with high compression, however, since the compression on all cylinders is the same, I would think if one or two plugs were not functioning, it would transfer with the plug when you swap cylinders. So I still think your problem is with a vacuum leak at the intake manifold. One more thing I might ask if the surface of the block or intake manifold has been resurfaced? That could affect the fit of the gland which could keep the manifold from fitting tight to the gasket and block.
Glad you are still around and working on T's. It's been a long time since I saw you.
Norm

[Craig Leach]

Hi Craig,
One of the performance issues of a model T is the 1-2-4-3- firing order. That is why Ed Winfield made the 2 up 2 down and it was so
successful. Considering this almost anything that effects 1-2 or 3-4 will adversely effect the other. It's apparent you have changed
ignition & plugs with no change. You have good compression. It sounds like you did a good job rebuilding the engine. So the issue
will most likely revolve around 1-2 cylinders the answer will need to be there. Fuel mixture or valve sealing are the most likely
as valves can seal differently at cranking speed than running speed if there is a significant spring pressure or clearance difference.
I will respectfully disagree with putting the engine in the car before I'm completely happy with it. Now that I have a run stand I
run a engine long enough to be sure when it is installed it's 100% I run a compression check & change the oil before it is installed
or put away fore future use. I once spent a whole day working on my Grandsons VW before I figured out that two plug wires
where crossed. So don't believe everything you read on the internet.
Craig.