How tight should a rebuilt engine be?

I suppose there could be many differences depending on the engine. I had an engine rebuilt and had it in my garage for eight years before I was ready to use it. It was incredibly tight. I used 12 V on the starter and towed the car with my tractor (very slowly in third gear), let out the clutch very slowly until I could hear the clutch start to grab and then hit the starter. When the fan started turning, I let the clutch all the way out and towed it about a mile. I did have the plugs out. It was enough to loosen things a bit. I reinstalled the plugs and towed the car again and I had it running in about 100 ft of towing.
Good luck with it. Ed
 
Had mine rebuilt by a local Model A specialist shop in late '80's; it was tighter than Dick's hatband and I had to tow it w/o plugs for a bit to loosen it up before I could start it with the 6V starter. It got better and better pretty quick and ran well. But within a few thousand miles it started to leak out the rear main and make a little noise; disassembly revealed that the rear main had broken up. I had the same shop rebuild it; also really tight for the first miles when reinstalled. Now it's Deja Vu all over again: I just pulled the motor last weekend to see why it's leaking out the rear main so much. I will pull the main cap this weekend to see what's going on; wish me luck, fellows!

In my experience a tight motor does not necessarily equal a good rebuild job. And if the bearing is broken up again you can bet that I will be looking for a different shop to pour the babbitt this time around!
 
I remember a lot of the old mechanics would build the engines so tight that they would have to pull them quite a bit before they could be cranked. Most if not all of them didn't hold up very long. I don't believe in a too tight engine. I set my rods and mains at .002 clearance. I aim for the block assembly to turn over on the engine stand at 55 foot pounds at the crank ratchet with a torque wrench. this has worked out good for me.
 
My new engine was tighter than a popcorn fart! I finally changed the battery to a more powerful 6 volt and it solved the problem. Prior to that I had tried different starters, battery cables and grounding points. The battery was the answer. Easy starting since then!
 
Most of the responses did not focus on "hand cranking". Yes, that will be a bit testy for awhile. Even removing the plugs will be a little tight to break it loose BUT then should turn with a bit of effort until you stop. Then you need to break it loose again. It shouldn't take much running/driving time before it becomes relatively easy to hand crank.
 
My fresh rebuild will moderately strain my 6 year old six volt battery and untouched for 55+years starter when cold and severely tax them when hot. When Hot I have to bump the starter past compression once before it will spin. I would never be able to start it with the handcrank due to the combination of stiff bearings and high compression. I can rotate the engine very slowly with the handcrank though with considerable effort and frequent pauses as it hits compression. I expected it to be stiff, so wasn't really worried, but was curious how my engine compared to others on the Ford Barn. Irene helped me out, work was cancelled Monday, allowing me to pick up the engine from the rebuilder, and work was agin cancelled Tuesday, allowing me time to install it. I can now climb hills in third gear with my Town Sedan that I formerly had to downshift to surmount. I am pleased with the rebuild.
 
I sense some mixed signal are being sent here. Is the engine tight from babbitt clearance -or piston-to-cylinder wall clearances?

Generally speaking, some builders set up the mains & rods very snug because they do not burnish the babbitt. Usually in this case, after the initial start up and running for a minute, if the engine is stopped and allowed to cool, the babbitt will have reformed around the journal pin and it should be fairly easy to hand crank. If the pistons are tight, THAT is a diferent issue and likely won't correct itself for a long time.

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If the pistons are whats tight, shouldn't you be able to rock the crank back and forth slightly indicating the crank moves freely but the pistons are staying in place? Or, will a new engine not have any slop in it like that?
 
Paul from Maine said:
How tight should a fresh rebuilt engine be? Should it be fairly difficult to handcrank when warm? Not worried, just curious.
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You will find that long stroke engines like the Model A will be harder to turn when rebuilt than, a short stroke engine. This is because of leverage on the piston. A long stroke engine has a faster piston speed in the middle of the stroke for the same RPM than a short stroke.
 
MrTube said:
If the pistons are whats tight, shouldn't you be able to rock the crank back and forth slightly indicating the crank moves freely but the pistons are staying in place? Or, will a new engine not have any slop in it like that?
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If the rods and wrist pins have the correct clearance. you will not be able to rock the crank. If an engine is set up correctly, you shold be able to turn the engine with the crank. If it is too tight to turn by hand, something is out of the recommended clearance.
 
JohnW said:
If the rods and wrist pins have the correct clearance. you will not be able to rock the crank. If an engine is set up correctly, you shold be able to turn the engine with the crank. If it is too tight to turn by hand, something is out of the recommended clearance.
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There is onlyone place the crank will turn without resistance from the pistons. This is at the top of the stroke for 2 and the bottom of the stroke for the other 2. This will be only for a slight instant as the rods rock over before moving the pistons.
 
Alignment of the crank hole with the pulley makes a huge difference on a stiff engine. My worn engine turned over OK on the handle , but when I replaced it (a '28 engine in a '30 roadster) with a reco '29 from Snyders, the crank handle bound up in the pulley ratchet with the extra turning effort. On checking, the chassis was bent half an inch to the right. When pulled straight, and aligned with the pulley, the engine would turn on the crank OK, though still stiff.
I also had too long bolts in the starter which bound up the flywheel. They were all the same length and fine on the old motor, but too long on the new one.
The final remedy was some thinned oil sprayed into the cylinders, which must have been too dry.
After all this, I could finally crank the motor with the handle to time it and the starter (6V) would turn it over.
It took about 3000 miles before it freed up enough to rock back on compression when switched off. Compression pressures are 90 to 95 psi on 5.5:1 Snyder head.
 
Probably from both babbitt and piston/ring clearance and increased compression. Thanks for bringing up the piston/ring issue. I was only thinking in terms of babbitt clearance and increased compression and had overlooked the fact that obviously the piston clearance would now be a great deal tighter. However the engine is behaving exactly as the rebuilder predicted. I've talked to him since the installation and it was like he was reading my mind about the performance and characteristics of the engine, both running and while cranking with the starter or the handcrank. So I am not worried at all or complaining...just curious about other people's experiences with fresh rebuilds. I just have this compulsion to understand what is happening since this is my first experience with a FRESH rebuilt engine.
BRENT in 10-uh-C said:
I sense some mixed signal are being sent here. Is the engine tight from babbitt clearance -or piston-to-cylinder wall clearances?

Generally speaking, some builders set up the mains & rods very snug because they do not burnish the babbitt. Usually in this case, after the initial start up and running for a minute, if the engine is stopped and allowed to cool, the babbitt will have reformed around the journal pin and it should be fairly easy to hand crank. If the pistons are tight, THAT is a diferent issue and likely won't correct itself for a long time.

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James Rogers said:
There is onlyone place the crank will turn without resistance from the pistons. This is at the top of the stroke for 2 and the bottom of the stroke for the other 2. This will be only for a slight instant as the rods rock over before moving the pistons.
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Never thought of that. Thanks for the insight!
 
A professional rebuilt engine should be too tight to crank start with the hand crank for the first few starts but should turn over and start with a good six volt battery. I remember when I installed a Marlar rebuilt engine in my 31 tudor back in early 2000. The engine was very tight but it cranked right up with the starter. I let the engine run for about 20 minutes, retorqued the head and changed the oil. I then cranked it back up and in my excitement I decided to drive it up town and show it off to the guy that owned the Parade gas station where we bought gas. This guy also had a model A that had been apart for many years in the process of restoration. We talked for a while and the guy inspected my work. When I got in to crank up and leave, the starter would spin but wouldn't throw the bendix gear to the flywheel so it could engage and turn the engine. What an embarassment. Not only that but I felt a slight chill up the spine as in what the hell am I gonna do now!!! I knew that the engine was tight but I got out the hand crank anyway. I know the happy look had left my face. There was a black guy nearby gassing up his car, I don't think that he had ever seen a hand crank and he looked at me like he wondered what my intentions were. I inserted the crank, gave it my firmest lift and it sprang right to life. everybody smiled because they had never seen a car hand cranked. I was happy because I really didn't know if I would be able to start the newly rebuilt engine in this manner. The problem was when I installed the starter I had sprayed some thin oil on the helix of the bendix and it wouldn't allow the bendix to work, out in the cold january temperatures. When I got back to my home shop I removed the starter, washed the helix of the bendix with lacquer thinner and had no more problems.
 
These comments help me also. I adjusted mains/rods to specs. (new rings) and all turned freely. When I put them all together the whole assembly was really tight and had to turn it over with a 1x4 lever at the flywheel (engine out of car). Glad to know that's normal.
 
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