Pistons in - how much drag is acceptable?

garmo

Member
Hi guys,

Just put new rings on my pistons, honed the cylinders to remove the glaze and had the crank polished and all new bearings. Now that I have the crank in, and the rods and pistons I'm wondering how much effort it should take to turn the crank. Seems the oil rings are fairly tight. All end gaps are within spec. The rings I pulled off of the tractor had huge gaps, some as much as close to 1/8" .

It has been about 25 years since I rebuilt a motor of any kind and would appreciate some feedback here.

There seems to be one spot in the rotation that is causing a bit of resistance more than in other areas.
This is a 1949 8N, with the thicker cylinders.
 
Yep, did you clean the carbon out of the ring grooves? A buddy of mine put new rings in his 289 Mustang back in about 1970 and when he got all of the pistons in he could barely turn the crank. Turned out that he had not cleaned the grooves.
 
I did clean the grooves well. I pulled things apart and used plastigage. The mains and rod checked out to be in spec. It looks like the #1 piston is ever so slightly cocked toward the front of the motor. I did not check the exact measurements, but there is just a bit more room to the rear side of the piston than the front side.

I can turn the crank with not a lot of problem using a 24" piece of square tubing. I just notice that at certain times I hear more of a scraping than at other times. I am not gouging the cylinder and everything else looks ok.

Maybe I am being overly cautious.
 
On two recent rebuilds I was able to turn the engine while on a stand with a socket on the pulley nut and a 20" breaker bar.
 
(quoted from post at 07:51:27 08/26/13) The cylinders must have some taper so you have to be careful measuring ring end gap.

Where did you get that idea? A freshly bored and honed cylinder should have as close to zero taper as the engine builder can get. High dollar engine boring and honing machinery goes to great lengths to ensure that. A top quality CNC engine shop shoots for something less than .0005 maximum taper - a low budget shop with a manual boring bar and hone is working closer to .001. The Ford 120 specification for maximum allowable cylinder taper when fitting new parts to a [b:6e651a5008][u:6e651a5008]worn[/u:6e651a5008][/b:6e651a5008] cylinder is .004, max out off round is .003.

TOH
 
Rope seals may be causing more 'drag' than old pistons in old worn sleeves, assuming rings/grooves are all good.
 
Thanks all. I pulled all the caps and checked clearance with plastigage. They all came within spec. This is my first rebuild with rope seals. I'm gonna put it back together and hope it is just that. It's not like I have to jump on the breaker bar, it is just a bit more resistant in certain places in the rotation.
 
(quoted from post at 09:50:11 08/26/13) Thanks all. I pulled all the caps and checked clearance with plastigage. They all came within spec. This is my first rebuild with rope seals. I'm gonna put it back together and hope it is just that. It's not like I have to jump on the breaker bar, it is just a bit more resistant in certain places in the rotation.

Every engine I have ever built taook more effort when the pistons went over the top and bottom. Sounds normal to me. New rope seals are a lot more drag than modern rubber ones and can make it very hard to turn at any position....

TOH
 
(quoted from post at 17:20:38 08/26/13) TOH,
Coupe doesn't need my defense but one could take his reply to mean that since Garmo did not replace the sleeves he "should" have some taper.

I considered that before I replied which is why I added teh bit about new rings in a worn cylinder. But it's not what he said so just consider my reply a more detailed clarification on the taper issue.

TOH
 
Most all rebuilt engines are tight and some more than others. What I do is before I put the head on, I put a generous helping of lite old, 10w, and crank the engine about 30 second. Clean the oil and do it several times. That will seat the rings somewhat. Sometimes with a tight engine it will run hot until broke in. I remove the lower rad. hose and stick a water hose(sealing with a rag) in the lower rad. and fill the water chamber. Leave water on as it runs out the lower water outlet in the engine. Crank engine a run for and hour or so. After that it should be smooth.
 
(quoted from post at 17:51:41 08/26/13) He did not bore the cylinder EXPERT.

I realize that and that is what I was attempting to clarify. There is no MUST when it comes to taper - the cylinders MAY have some taper if they are worn.

At this point in my life I no longer consider myself to be an expert in anything. When I was younger I thought I was an expert in some very specific technical areas of my chosen profession. As I got a bit older and my professional circle got a little bigger I demoted myself from "expert" to "knowledgeable". From there it was all down hill to simply "experienced in a wide range of topics" :cry:

The one thing I have learned in that developmental journey is to continually strive to readily acknowledge my errors with a semblance of grace and humility :idea:

TOH
 
Are you sure thqt you put the rod caps on the same rods they came off? They are not interchangable and if you mixed them you have a problem.

Zane
 
I am certain they are where they belong. They were marked by someone before me. I kept them the same.

I put the crank and pistons in today. I can turn it with an 18" breaker bar. Seems tighter in some places but I think I'm ok.

I left the crank pulley on and now I see it must come off to put the timing cover on. I need to go buy a socket to get it off. I don't have a 1" socket.

Tis is taking longer than it should. I broke my ring compressor. Spent about an hour fixing it, then it broke in another place. Not fixable any longer. Had to borrow a compressor to get the last two in.

Now I'm stuck till I get a socket.

It's always something.
 

I am with the rope seal contingent. You may have to turn it over with the wrench for a half hour to flatten the rope seal out enogh to get it to where the resistance is moderate.
 

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