TN 28 total rebuild

[tinkerman]

Ok I’m ready to start rebuilding my TN 28 after much help locating parts. I’ve got new crank pistons connecting rods and wrist pins as well as gaskets and rings. Checked the rings by dryfittimg in cylinders and measuring end gap and filing ends until I hit the middle range of clearances. Checked ring grooves in pistons for clearance and this too is good then checked clearances between cylinder and piston, ok there. One thing I noticed was if I tried to stick the outside edge into ring groove in piston that a couple of grooves wouldnt allow the ring to “bottom out” in the groove. I took an old ring and used as a scraper and tried cleaning the back of the groove up a little and never got it to completely seal. I installed the rings pistons and crank. No sealant yet but dryfitted the lower half of block and snugged 4 nuts down. I have to put a crescent on the flywheel nut and use moderate pressure (stiff) to get the crank to turn. I don’t think this is normal. Do you think the grooves in pistons need more “cleaning up”?
Any help is appreciated. It’s gonna turn 1500 times the first minute I start it so a little turning and disassembly and reassembly shouldn’t hurt if need be, right?

It's a jungle out there.

[frankr]

I ran into that problem myself, several years ago. The rings bottomed out in the grooves. As well as I can recall, it was the result of superseded parts not fitting older applications. Sorry, I don’t remember all the details or how I dealt with it. Perhaps somebody else will chime in and take it from here.

[tinkerman]

Well I don’t think the rings are the issue now. I loosely put rod caps on the crank and hand tightened a couple nuts on the other half of the block and the motor spun snug but freely. However if I tighten the rod caps it gets a little snugger and if I tighten the other half of the block it’s pretty stiff to turn the crank with an 8” crescent wrench. There is no gasket between the two halves so maybe the sealer is “just enough” to loosen it back up some? Time will tell

It's a jungle out there.

[Mumbles]

Do those rods and caps have alignment pins? If not, you should tap them lightly near the joint while tightening the screws. This is how you seat them to the crank. Doing it on the bench first will give you an idea how this works. This way you can hold the crank in your hands and spin it to check for drag before doing the final assembly.

It goes without saying to mark the rods and caps before disassembly so they can go back together on the same journal the same way they came apart but hey, you already know that! ☺

[frankr]

Yep, caps cannot be swapped between rods, and cannot be turned end for end. Align the match marks

[tinkerman]

Yes , did this but not as easy to tap with hammer as they make it sound due to not wanting to damage crank with a mis lick so TAP I did (and yes marked rod caps and facing right way and on correct piston with same bolts in same holes) I guess if you havnt rebuilt any of these engines before, it’s hard to gauge what is too tight and how much leverage you gain with the flywheel installed

It's a jungle out there.

[tinkerman]

I think I’m gonna take both halves of the block with the pistons and crank to a machine shop and see if they will assemble it and check clearances . Somethings still not right and I’ve got several $ tied up in parts. Just seems something is too tight and I still havnt torqued the other half of block. I put it in a vise with these bolts snug and put the flywheel on temporarily and pulled with a rope and I’m certain when I torque the bolts down itlll be “too” tight to pull with a rope

It's a jungle out there.

[Mumbles]

Hey, hold on. Something isn’t right here. Before you go to a machine shop, lets do a little bit of back tracking here.

In your opening post, you mentioned you got new parts for your rebuild. They were a new crank, pistons, rods, rings, wrist pins, gaskets, etc. Were these parts brand new original parts or new to you parts from another used donor motor? I’m just wondering because it can make a difference. Also, why would you want to replace all of the internal moving parts? If they were worn or damaged beyond repair, the block should show similar signs of wear or damage.

You can check the crank for free running by lightly oiling its main bearings and putting the two case halves together. any binding here and you can suspect your crank might be bent.

Also, try loading each piston individually with its rings and install it into its respective cylinder one at a time. Don’t forget to oil it. A certain amount of drag will be felt with new rings in a freshly honed cylinder but any sign of tightness or excessive drag means something aint right.

After seventy years or so of use, the cylinders have probably worn to a taper shape, wider at the top and narrower at the bottom. The minimum end gap of the new rings has to be checked at the narrowest area of the cylinder they will see, which is below the intake and exhaust ports in the relatively unworn area of the cylinder. Setting the end gap of your new rings at the top of the cylinder may cause binding as the motor is turned over.

Double check, triple check your work as it’s probably something really simple causing the issue. Chances are, the machine shop might not have the time to be able to figure it out or want to work on it either.

[labrador-guy]

I was going over this tread again at I was reminded of a problem I had a few seasons ago. I was working on a motor that had water in it and was mildly stuck. A few smacks with a hammer and a block and it came apart. I decided to get some new rings and I fitted them to the cylinders. Did a lot of cleaning and some honing. When I went to assemble the pistons in their bores they were way to tight. I could barely move them up and down. After some rechecking I found that the ring locating pins had moved out some. (toward the cylinder) Maybe from ice, that moved the rings out and way to tight against the cylinder. Just a light smack with a punch and I moved the pins in a little and it cured my too tight problem! Something you can check when you get back into that motor.

dale

[tinkerman]

Mumbles you made a great point with the ring gap, as you suspected I DID check end gap towards top of cylinder and should check at the bottom. The motor was seized due to moisture I believe and rings were beyond stuck. I destroyed a piston and rod unseizing the motor.i was fortunate and found NOS pistons, rings, rods, wrist pins and a new crank also (very reasonable price) the old pistons weren’t scored and neither is the block so I thought would be a good rebuild candidate. Without the crank installed (just pistons with rings in cylinder) the pistons feel “right” thru the entire stroke, no drag. I agree I should try installing just the crank and torque the lower block and check resistance and narrow it down to crank clearance issue and if not the issue then attach the rods to crank and check again. Process of elimination thanks for the reply’s sometimes just need a nudge in the right direction.

It's a jungle out there.

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