Help/advice on reinstalling pistons

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Model T Ford Forum: Forum 2012: Help/advice on reinstalling pistons
Top of pagePrevious messageNext messageBottom of page Link to this message  By David Kriegel on Monday, July 16, 2012 - 12:50 pm:

I have a problem and need your advice

My touring had low compression, 22 psi would run poorly

I pulled the head, reground the valves, pulled the pistons. The ring gap was HUGE 3/8 inch but piston cylinder was only 0.10 over

pulled pistons keeping them in order, marked to replace in correct direction to the radiator along with matching rod caps

On reinstalling piston rod caps, had to really tighten cap bolts in order to place cotter pin in rod cap bolts

now engine is too tight to turn over

I suspect too tight of rod caps on the crank

I propose if you think this is the right course

1. Pull all rod caps

2. replace caps one at a time checking free movement of engine

3. If one cap is too tight add a few shims

until it just moves free

I am a good parts re placer and learning mechanic so I will appreciate advice


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Monday, July 16, 2012 - 12:55 pm:

several things may have occured, but suspect that you may have placed one or more caps on backwards or put wrong shims in wrong location(s) for the rod caps. There will be marks on the rods and caps...marks belong on the same side.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Monday, July 16, 2012 - 04:47 pm:

Are you sure that the caps are on the same rods from which they were removed, and that the rods and caps are in the same direction as when they were removed? Most rods and caps have numbers stamped into one edge near the bolt. That number is in order from front to back in the engine. The cap should have the same number as the rod, and the numbered sides should be together. When the rod is installed, the wrist pin bolt goes on the side toward the camshaft.

When you get all the right parts lined up, next thing to do is to loosen all the bolts about one turn. At this point you should be able to turn the engine using the crank. Then tighten one rod at a time. If your auto parts store has plastigauge, get some and put a strip in the bearing from front to back and tighten the cap. This strip should flatten out and there is a scale on the package which compares the width with the clearance. It should be .0015 inch. If it is less than that, add a shim and try again. If it is more than .0015 remove a shim. When you get it right, loosen a turn and go to the next rod. When you get it right go to the next etc until all are adjusted. Each bearing should be oiled as you do this adjusting and after all are adjusted turn to 30 ft lb torque. and place the cotter pin. If the pin doesn;t line up, remove the nut and file down a little and try again. Do not over torque the nuts. When you get all 4 oiled and tightened with the cotter pins in place, you should be able to turn the crank. It might be hard to turn, but nevertheless you should be able to turn by hand. Then place the inspection cover and pour in the oil. If you have a starter, it should turn over enough to be able to start the car. If not, try pulling the car with a long rope from the spring shackle or frame. Do not pull directly on the axle. Try pull starting it in high gear. Once it is started, let it warm up and then re-torque the head to 50 ft lbs. Drive slowly and do not let it boil for a few hundred miles and it will be broken in.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Monday, July 16, 2012 - 08:21 pm:

If you have mixed up or rotated the rod caps you need to lightly coat the babbitt surface with Prussian blue and retighten the rods just past snug. Then rotate the crank 360 degrees or more. Remove each cap and look at the bearing surface. If its shiny, virtually all across the Babbitt surface, then its correct. If you see a little shiny surface and considerable blue surface its the wrong cap or the correct cap turned 180 degrees. If the rods didn't knock then then there is no need to remove shims or file the caps.

How did you measure the ring gap? If you have iron pistons you could install the piston with rings slowly upside down in the cylinder and note the ring gap. This would be more difficult with aluminum pistons and a narrow piston ring. If its 3/8 inch, then you have a problem and should install new rings. On your cylinder measurement, do you mean 0.010" oversize, 3.760 inches. I don't think your 0.10" is correct.

You need the Model T Service Manual and the MTFCA Engine Manual. They are inexpensive and will get you going in the right direction.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Tuesday, July 17, 2012 - 06:02 am:

something else that I just saw upon rereading your initial post...if you are looking at the ring gap when the rings are out of the car, they will be large. Ring gap is measured when the rings are installed into the cylinder, not when they are loose.


Top of pagePrevious messageNext messageBottom of page Link to this message  By CharlesHebert on Tuesday, July 17, 2012 - 07:36 am:

Something else...you may try plastigauge to measure your rod cap clearances. Yo can buy it at auto parts stores..


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