I've noticed that my '24 Touring seems to be pretty gutless, even for a T. I decided to check my compression, and all the cylinders measured in at 45 +- 2 psi. I hear that it should be around 55-60 in a strong engine. My question is, what could cause the compression to be so consistently low?
Here's the current status of my engine:
Iron pistons with new rings. It does not burn oil and the spark plugs show no signs of oil fouling.
Valve seats are shot, but the valves are new. Ironically, the cylinder with the worst seats showed the best compression.
New valve springs.
Cam and timing gears are original, and the cam bearings are fine.
Furthermore, what could cause the engine to feel so gutless? I've driven many other Ts before and mine doesn't seem to have as much pep as some of them. The ignition timing is right on and the carb has been rebuilt. It starts extremely easily and frequently gives me free starts (especially when cold), yet has trouble keeping up at speed. Hills are a chore and it has a difficult time getting up to 30 with four people on level ground.
I haven't the same experience with T's as much as many other guys here; more with other cars. One of my biggest questions would be the valves. You mention you have new valves, but bad seats. Did you check how the valves seat, even on the bad seats? Did you lap them in to get a good "seal"?
Mine is a '13 and also puts up 40-45 psi on each cylinder.
If you think about it... If a cylinder is sucking in a full stroke of air, and that air cannot go anywhere when compressed (i.e leak out somewhere), then that stroke and combustion chamber volume will yield a theoretical compression of X ( measured in psi by your gauge)
If air is escaping or if the cylinder cannot suck a full stroke of air, then it cannot attain that theoretical compression of X.
My T is in the low psi range as I said, but it frequently runs out of revs on hills and has to be slowed down! I had 4 adults, 2 toddlers and a baby on board at +- 5000 ft above sea level and was keeping top gear up moderate hills.
I also have cast iron pistons (original heavy type) with newish rings, and I run a Holley G and KW coils, although it did the above on mags of course.
I have just stripped this motor and mic'd it up. It had excessive wear on the rings, and only 1 valve was cleanly seated, the rest were black and one was about 1/3 shiny if that makes sense.
To me, if the rings are in spec, and the valves All seat properly, then you should get close to that theoretical compression of X.
What I would suggest is... to find the source of your low compression, is to see if the cylinders will hold the 45 psi for any length of time. Some guys talk about oiling the top of the piston on the compression stroke and seeing if the gauge will hold pressure or not..
I've not done this, and it sounds like it could be more difficult than I am explaining, but it sounds plausible to help you determine if its the valves leaking...
If it holds, then maybe you need to look at the piston and piston rings.
But... if it turns out that your cylinders are holding pressure, then turn your attention to carburetion and/or spark.
This forum is a wealth of information, and the experts here will have engineering degrees where I do not, but what I have suggested is how I look at the problem, and what I did to have a well behaved T.
I hope this helps, and all the best in diagnosing your problem.
The quality of the ring to cylinder wall interface and the quality of the valve to valve seat is the most important thing you do to make power.
The valve job needs to be done properly, which means cutting the seats and grinding the valves properly. Installing new valves without doing this is not going to produce good results.
The cylinder walls need to be smooth and not have excessive taper. If there is too much wear in the cylinder walls you will have excessive ring end gap. That costs power and causes oil consumption. Of course this depends on the ring end gap being within limits too.
A worn camshaft can cause reduced cylinder pressure.
Stuff you can do with the engine in the car - grind the valves, replace the camshaft, and install an aluminum high compression head.
Installing a high compression head will not fix the problem. In fact it could make it worse. You first need to find out why your compression is low. You can do this with a leak down test. You modify a spark plug with a tire pressure valve and install it in the spark plug hole. Then with the piston at top dead center and both valves closed, fill the cylinder with compressed air and listen for leaks. If it comes out the intake or exhaust it is leaky valves. If it comes out of the oil filler, it is leaky rings.
New rings can cause low compression until they seat. Put a few miles on the engine and check compression again. All spark plugs should be out and the throttle full open when you make this test.
If you have good compression, a high compression head will raise the compression, but if you already have low compression it won't help.
I don't know how worn your cylinders or valve seats are, but if you still have the cast iron pistons, and the engine has many miles on it, I would think you need a full rebuild, not just rings and new valves.
Cameron at 45 Lbs. you're not in a "very bad place" at all. Granted a good valve job might give you another 5/6 Lbs of pressure and improve performance but unless you're pulling long upgrades, which are hell on a T anyway, don't go nuts right off. How are the coils? New capacitors? HCCT set up? Timer properly set and being used correctly? Carb main jet needle set OK? Don't jump into a tear-down without some checking first.
Cameron, When you put new valves in, did you remember to correctly re-cut the seats? Or are the valve seats too recessed? Remember that when you install new valves you have to lap them in at a minimum. Better to re-cut the seat (seat should be a degree or two less of an angle than the valve). If you don't have a decent Neway valve seat cutter, you could probably rent one pretty cheaply or borrow one from a local club member. Once cut, you need to lap those valves in as well to get a good seal. Good luck!
I agree with Charlie B, 45 lbs is not terribly low. I will say however that I have never ever rebuilt a T engine without boring the cylinders and installing aluminum pistons at least 30 over. Also you need to rebuild your valve seats or you might not ever increase your compression. How many miles do you have on your new motor? You WILL RUN BETTER after its broke in.
I would check for a leaky head gasket and leaky spark plug threads as well cheap fix if that is part of the problem.
I would lean towards the kind of things Charlie posted above. I thought my T was kind of gutless until I installed new properly adjusted points, clean plugs and especially new coil capacitors. Leaning out the mixture a bit seemed to help as well. I now consider my T to be rather fast.
you weld a fitting on an old spark plug base to plug in your air hose. put the piston at top dead center and blow low pressure into the cyinder for your poor mans cylinder leak tester. listen...air out the carb? intake valves, air out the exaust? ex valves, air out the breather? rings. just patching any of the above will not make a good motor, really dave is right, a complete rebuild for a strong healthy motor will make for more fun and more reliable touring. its only time and money!
All good advise above, just to make it all as clear as mud.
Lost of power or lack of can be a number of things. You really are in the wheel house with your compression ratio, assuming your are running a Ford high head (low compression), on an older engine.
You state that all cylinders are within a +/- 2 psi, which is kinda of normal. All the spark plugs look about the same color? A difference between 1-2 and 3-4 would indicate a leak on the intake manifold, which will rob power.
You can check the quality of the rings seating in the bores by running a compression check, record, and the do it again but squirt oil into the cylinders, it will increase a little but if you have big gains in pressure, your ring seal would be in question. Remember to remove all the plugs and have the throttle wide open when doing a compression check.
If all look good then a leak down test would give you an idea of the valves seating correctly.
Assuming that nothing really jumps out with the test.
What gears are you running in the rear end, 3 to 1 gears in a touring with 4 people will not pull the hills very well and on flat land would have to work to get up to speed with a load.
A stock cam that is worn out would also cause a lack of power, and really is a big factor in engine performance.
The best bang for the bucks is to put a high compression head on, next would be to put a good cam like Chaffin”s or Stipes new cams. I like 250” lifts in heavy cars with loads for hill country pull. I am not a fan of re ground cams but that is just me.
My 2 cent worth, your mileage may, will vary.
AH ! to have 45 PSI ! My second car down the road to do will not hand crank start despite new coils, strong spark and a rebuilt carb. Wonder why ? About 15-20 PSI ! I am working on a nice 1926 that has the same problem
I do need recommendations on a tool to CUT the valve seats, as I believe my lapping job has been too inadequate
You can check the ratio of the rear end by putting the car in high gear. If you have a Ruckstell put the lever forward. Then note the location of a tire valve stem and pull your car forward with the hand crank. spin the crank all the way around in the same notch. You might need someone to help you by pushing the car as you crank it. Count the number of crank rotations for one complete rotation of the tire. If you have 3 crank rotations, your ratio is 3-1. The standard ratio was 3.6 to one. So you would have just a little over 3 1/2 turns of the crank to one of the axle if you have standard ratio. Mike Bender is right. The 3-1 ratio works OK on very flat country, but in hills you will do better with standard ratio.
Thanks for your replies!
Let me see if I can address a few of the questions and comments people have made.
I lapped the valves like crazy and they seemed to seat well and make a good seal. I couldn't afford to have the seats ground, so I made the best with what I could.
I have rebuilt my differential and it is completely stock with the 3.63:1 ratio.
The best I could do to the cylinders was hone them. I have no idea as to what condition they are in otherwise.
I'm running my electronic coils, and they work beautifully. Getting the magneto working and going back to stock coils is on the list when I do a big rebuild.
The head gasket is new and had been coated before the head was put back on.
The spark plugs are all a nice tan color, which really surprised me.
Did you torque the head after it was warmed up? They can loosen up the first few times the engine warms up and then leak.
The valve seats should be narrow about 1/8 inches wide. If they are wider, they can trap carbon and leak. That is the reason for the 3 angle grind. If they are sunken below the top of the block or if the seat is cracked or severly pitted, they should be replaced with inserts. You also need to remove some from the valve stems and check for valve timing. See book on Engine for details. Unless you have adjustable lifters. If they are adjustable, you might not need to cut off the valve stems. If you have a new or reground camshaft you can use recommended clearance for the gap instead of valve timing. All the above will effect compression.
Lots of good ideas, but I like to think outside the box at times. Have you looked to see what gear ratio you have in the axle? If you have a high speed ratio, you will not have enough power with a touring body.
The first T I bought turned over free, but lacked compression, it turned out that it also lacked pistons.
"The first T I bought turned over free, but lacked compression, it turned out that it also lacked pistons." OK this post really gave me a laugh !!
One of my cars went from a good pulling car to one that could not climb a hill, yet it ran fine on flat roads and never missed- just no power. I was constantly having to use the Ruckstell, where others on the tour would make the hill in Ford high. I slowed everyone behind me down.
Upon dis-assembly, the fiber timing gear had sheared at the 2 cam pins & turned a bit. I installed a new timing gear and the car was back to it's old self.
I'm thinking that you might be on the right track here. My T has the cast iron timing gear, but it may be loose (which would also explain a very difficult-to-trace knock that I have). I don't remember how I tightened it, but it may not have been enough.
As I recall, my T used to pull hills real well, even with two hefty guys in the back seat. Now it seems to lack power and has a hard time getting out of its own way. I never did any sort of compression test back then, so I can't compare it to the readings I got about two months ago.
If the timing gear is loose, it can certainly cause a lack of power, and that strange knock. Next time I'm out there, I'll pull the generator and check that pesky timing gear!
45 psi is a 4:1 compression ratio, 60 psi is a 5:1 compression ratio.
if you want to make a "poor mans tester" as noted above, no need to weld on a spark plug base. Model Ts are 1/2" pipe thread.. so just go to lowes and get a 3" section of steel black pre-threaded pipe and adapt an air-compressor quick connect to it. easy as pie