View Full Version : 45 Piston Rings Clearance
I'm putting new rings on new pistons, and found the end gaps to be OK, but all 6 rings have between .001" and .002" side clearance.
How can I get the specified .004" side clearance?
Bore clearance or piston ring land clearance ? Paps
The ring grooves aren't wide enough, or the rings are too thick. (vertical measurement).
If you need only a few thousanths taken off of your rings you can have them Blanchard ground. Since it would only be a couple of thousanths to be removed, it won't matter which side you remove the material from. Before you do this though, check to make certain your piston grooves are not burred or rolled over at the ring land edges. Removing these can be real tedious work if done by hand. Machine tool removal is easiest but indicating the piston in is tough. By hand, you can dress them lightly with a fine tooth thin file with fine grit emery cloth wrapped around the file blade. You can also try a ring groove cleaning tool to make certain there is not a film of foreign material on the lands which would restrict clearance measurements. Paps
03-05-2007, 09:01 AM
Rex.... Being as these's are new parts your dealing with I would suspect you'll find a slight burr over the piston grooves, caused during final machining of the O.D. of piston. As Paps stated, Give those grooves a close look. A quick run around the grooves with emery may be all you need to do. Good Luck with it. -Steve
Paps & O.R.-
Upon your advice I've found the following today using a micrometer and 10x lens.
Compression rings actual thickness: .0930" spec:.0937"
Compression ring grooves: .0095" with a nice clean bevel.
I also inspected the rings for burrs, etc. and found none.
The odd thing is, when I put the ring o.d. side into the ring groove, it can't go all the way in and touch the groove's interior wall. It gets stuck between the top and bottom wall. It seems that the grooves aren't quite square.
I measured my ring groove cleaner and found the closest size cutter to be @ .093" and of no use.
I'll consider trying the emery paper or put it on the lathe and touch up the grooves.
Paps- What is Blanchard grinding?
03-05-2007, 08:32 PM
When I figured this side clearance thing out, I stopped sticking pistons in UL's.
A bell went off in my head when an old timer said..."I used to have one of those things; if I kept it above 75 for too long it'd seize a ring".
You can lap them on a piece of glass (or other flat surface) with sandpaper taped to it.
I think I use 220, then 320.
To avoid wearing out your fingertips, put a coarser piece of sandpaper on top of the ring, and that will grip the ring while you rub it around on the bottom piece.
Even better...put the coarser piece on a block so you get even pressure.
Yesterday I saw an post in another cycle site that showed a fixture for doing this operation.
In a block of steel, they cut a relief the same diameter as the engine cylinder, with a depth slightly less than the thickness of the ring. The ring is then compressed, inserted into the relief, and lapped on 400 grit paper soaked with solvent.
It seemed like their purpose was to face the ring surface, not to change it's dimension, as they showed only .0005" protruding from the fixture.
When doing this, how do you know when you're done?
There's a good article on the function of this group of parts at www.aircooled.net.
03-05-2007, 09:27 PM
Originally posted by Rex
When doing this, how do you know when you're done?
Trial and error, my good man!
Slip it on the piston every now and then and use a feeler gauge.
Blanchard grinding is a machine make name. It uitilizes a rotary/osiclating magnetic holding table that operates under a high speed revolving wheel with a set of grinding stones on it. The machine can be fed in increments of less than .0001" Coolant is constantly fed over the part being ground. Most machine shops own them. Dusting off those rings would take but a few minutes with a Blanchard grinder.
Skin cutting the piston groove lands will be a tough and tedious chore. Setup is the difficult part. A great deal of patience is a must also. The grooves will need indicated in both laterally and circumference wise. It would be advisable to use a last word indicator with a very small ball tip on the indicator stylist to check both sides of each piston groove lands so you can determine which land is tapered. Set the indicator up on the cross feed and run it in and out along the sides of the ring grooves to check for the tapered side or sides. Both sides may end up being tapered. I myself, would grind a couple of high speed tool bits to a point, a left hand and a right hand. Then I would put a micro radius on the tip of the tool bits according to the ring edges that fit that particular groove. You don't want to change the ring groove bottom corner clearances. Cut only the sides of the ring grooves that need trued up. Other difficult parts of this operation ? Determining when to stop the tool bit as you near the bottom of each ring groove and how to set the tool bit for the cut that will be taken on the ring land wall. A pair of indicators setup for both axis travels will gauge your moves in relation to the tool bits. Cutting fluid and slow rpm, along with a very minute feed rated will insure a smooth finish. Paps
I don't like the hand lapping of the rings technics. It is to easy to get them all out of whack that way. This is do to the un-equal pressures over the entire surface of the ring, that cannot be avoided, while hand lapping them. Thus my suggestion of Blanchard grinding. Paps
03-06-2007, 12:35 PM
I wouldn't grind the rings. What you'll end up with is custom made rings to fit a poorly made piston. What happens if you need new rings in the future? You'll also have an issue with improper support of the ring. Those grooves need to be square. Pistons are one of those parts that are spit out by the dozen on CNC lathes It sounds like there was a breakdown of the grooving tool during the machining process. The giveaway is the tapered sides on the grooves. Too many manufacturers are using their customers for inspection and quality control. Paps' instruction is excellent but an easier way would be to exchange the pistons for some that are made correctly. If the supplier won't stand behind their product for an issue like this I'd be leary of using those parts at all.
I'll second all of that Kojack. Dusting the rings a couple of thousandths will work though, if the land taper is not on the load bearing sides on the pistons. Most definately easier to exchange them or buy a new pair for sure. Paps
Thanks for the many and varied suggestions for fixing this problem. I think if you do a forum search of my name you'll find this type of issue to be constant.
It seems as if I have difficulties in only three operations:
1. When fitting new parts to old parts.
2. When fitting new parts to NOS parts.
3. When fitting new parts to new parts.
Notice any common elements?
The pistons were bought and installed during a botched rebuild @ 5 years ago from a source unknown to me, so exchange isn't an option.
The badly done parts that I have returned in the past resulted in either an exchange for another new bad part, or a "store credit".
I don't have the feeling that buying more new parts will help me.
If you know of a source of +.040" piston/ring sets that will guarantee (money back) all the dimensions will be correct when I take them apart and check them, I may consider buying new.
Unfortunately I've already paid for having the cylinders and wrist pin bushings fitted to these pistons and pins. If I do have to start over, should I buy a +.050" set?
03-06-2007, 07:39 PM
this is one of the reasons i like buying a barn fresh bike, tearing off the heads, making a jig,picking up a mallet ,pounding the pistons loose ,install the heads ,add gas AND GO !(i did this )
03-06-2007, 07:40 PM
ps , its still running 6500 miles later
Lucky SOB !! :) Just kiddin with the SOB part. ;)
Yep...work the fits on what you got then. But ??? If you run into bad troubles ? I do have a set of NOS OEM .060" oversize pistons with rings in their original boxes. They are oem nos HD original. Alas though...I provide no warranty, even though they are HD. Really pricy too !
Good luck with the re fitting of the ring grooves Bro. If you need any additional help, feel free to email me direct. Paps
03-07-2007, 04:07 AM
Re-cutting the old grooves sounds like a good option. The problem is that unless you have access to a lathe you'll have to farm the job out. Machine shops ain't cheap and I'd bet that you'll get charged 2 hours or more for that job. New pistons with pins and rings (which BETTER be guaranteed) are around $90 each and I'm not sure that you could get your old pistons cut much cheaper than that. If you have a friend with a lathe now is the time to look him up.
It will take them a hour each just to true them in on the lathe. You are looking at 3 hours. Ask a friend indeed or save those pistons for bookends.
Kojack........how do you waranty original nos oem antique HD parts when HD themselves don't sell them anymore ? ;) If I sell or purchase a an nos oem part in original packaging, I have no way of knowing if they are corroded underneath. I have uncovered some really pristene parts but I have also uncovered some real eye sores as well. Now if we are talking new production parts from any manfacturer, don't buy without a full warranty on defects in materials, workmanship, and craftsmanship. Paps
03-07-2007, 11:47 AM
I was talking about new aftermarket pistons, Paps. The prices are from 45 Restoration Company, a reputable dealer. I once purchased a set of NOS rod bearings for a 741 Indian in the original WWII cosmoline packaging at a swap meet. When I handed them over to the guy who was building the engine he warned me that there was a good chance that they'd be junk. I lucked out and they were OK. I bought a couple of valves the same way and they were junk, rusted right in their original wax covered package. I didn't pay much for them however. You're right, it can go both ways. NOS parts sold by a third party can be guaranteed but that's the choice of the seller and he should make that clear before the sale. If you really want to get top dollar for a part you should stand behind it for things like size and condition. If you're selling a part just because it's in the cool original box than that's OK too, just make it known. I've seen that happen lots of times. I wonder if anyone could guarantee the actual perfomance of a part however. When a piston does fail it can be impossible to pinpoint the cause, at least as far as satisfying a warranty goes. Too much depends on handling and installation. Pistons that have been rattling around loose in a box of junk won't be my first choice for a rebuilt motor, that's for sure. I've come up with some other uses for those.:p
Now that is cool !! Nice work !! Not to stray far from the topic, but, I once bought an nos oem 45" pinion shaft wrapped in it's original military dressing. When I uncovered it, the pinion splines were not machined onto it. Bet that would surprise the motorpool folks. ;) Paps
Got a lathe in the shop, a brother for a machinist, and a fair amount of time since the heads are out getting new sparkplug holes and are not done yet.
I wouldn't advise this hobby to anyone who doesn't have a lathe, mill, tooling, and someone to run them.
03-07-2007, 07:02 PM
Sounds like you're good to go. Groove depth isn't critical, as long as the the ring has at least enough back clearance to allow it's face to be recessed completely into the groove. Too much is OK, not enough could cause seizure. You already know about the side clearance. Good luck.
I found just the thing for this project at
Scroll down to item PGC 150
I agree with everything Kojack just stated. Depth has to be deep enough but just don't cut clean throught he wall. :) Seriously though, if you do skin the bottoms, blend them in with the sides smoothly and with a minute radius at each corner. Make sure the radius is not to large as to be restricting to the inner ring edges. Sharp corners make for weak corners. Fracturing may occur at the point of a sharp corner.
You have the tooling needed. Have fun and enjoy the results.
Oh Yeah !! I clicked on the link Rex, but only got an email addy. Paps
03-07-2007, 11:34 PM
Here's a working link (http://www.mondello.com/Catalog/mondello_blueprinting.htm)
Thanks Perry. There is a bunch of nice equipment on that site. That indicator is equal to a last word type manufactured by Starret and other manufacturers. Paps
03-08-2007, 07:58 AM
It only takes me about ten minutes at most to set up a piston on my Logan,... What am I doing wrong?
03-08-2007, 09:24 AM
I don't know what you're doing wrong but I could watch and let you know. :D Seriously, I would say that's an average time if everything goes well. If you have a quick change tool post and a good insert grooving tool you could do this whole job in under an hour. Then again, I've seen some old 3 jaw chucks that you'd never get to run true without a lot of shimming and cussing. It all depends on the equipment you have to work with. I worked in a machine shop for a long time and learned it's best not to comment on how long it takes someone to do a certain task. Getting it done correctly is more important. Notce though, that I said you'd likely get charged for two hours. I also learned how machine shops bill.
03-08-2007, 07:12 PM
Who needs a chuck?
That just gets in the way, or scars the skirts if you actually try to use one.
Cotten...You checking all TIRS when you set one up ? All ring grooves running true, all diameters dialed in, wrist pin on center to diameter, piston face running out ? We are talking about conventional machine tooling, not 95% contact precision collect production machine tooling where an operator needs only to load and unload parts.
Three jaw chucks are for roughing or don't mean much parts. Great for polishing at best. Never saw a true running three jaw. Close to true, give or take a thousandths, but never true. What do you do when a part moves a tiny bit on ya ? Change it to a four jaw, that's what. Might as well have setup the four jaw in the first place. Four jaw is the only way to go when finishing critical works. Holding power is better and more reliable than any three jaw. Never trust a three jaw for precision work. You can't dial it back in like you can a four jaw. Three jaws have a tendency to spin loose around a part too. Try chasing threads with a three jaw. If the chuck spins loose from the part or the part moves, try picking the thread back up on it. That is a nightmare enough with a four jaw, but at least it can be done. Paps
Scaring is a lack of softjaw usage, over tightening, under tightening, or a combination of some or all. Paps
03-08-2007, 07:34 PM
For Gawd's sake,...No jaws!!!
Just draw it up onto a faceplate.
(Using a drawbar through the headstock with an eye to pull on the wristpin.)
The bottom of the piston is cut square to the ring lands. A dial indicator and a small wooden mallet will true it quite close to its original axis with little patience at all, and the drawbar will secure it most firmly.
03-08-2007, 09:15 PM
Hey guys, letís not come to blows about this. Iím sure there are many methods. Cottonís method is common. Iíve never seen it done on a face plate though. If the bottom of the skirt is square, and it should be, that should work fine. Iíve seen it done with a flat plate that holds the piston the same way and is then held in a chuck. The plate and piston unit can then be easily adjusted to run very true. If I knew I was going to be doing pistons on a regular basis Iíd definitely make one up. Cotton, The shop I worked in had over a dozen engine lathes from 6Ē to 96Ē (plus CNCs) but not one face plate. Some of the chucks had t-slots that weíd use for some setups, but that was mainly on the big verticals. Maybe if Iíd had a chance to live with one Iíd like it but I think I can do anything with a chuck that can be done with a faceplate. When I started my apprecticeship the shop used to re-cut the ring grooves oversize for Alco diesel pistons. We used a four jaw chuck. Weíd chuck on the head of the piston with the top ring groove just past the chuck jaws. The head is thick enough that it wonít deform. We put small pieces of copper between the jaws and the pistons to prevent dents. We had a counterbored plate that fit on the skirt end to allow us to run a live center for more support plus it aided in holding the piston in place against the chuck during setup. If youíre thinking you needed three hands to do all this youíre about right, but we managed and with time you got pretty good at it. A 45.piston head doesnít have as much room to chuck on as an Alco but thereís enough and it can be done the same way. The piston is light and you wouldnít need to support the skirt end. Youíre just skinning the grooves, not roughing. I donít think chucking on the skirt is a good idea. Itís too easily deformed. Besides, Iím not sure but arenít 45 piston skirts slotted? Paps, I agree with everything you say about three jaw chucks. Fours are better 95% of the time. I donít work in a shop anymore. I have a friend with a 9Ē South Bend and all he has is a three jaw chuck. If thatís all you have, you use it. The depth of the ring groove isnít critical. If I can get the side of the groove running true and the bottom is running out a thousandth or so, Iíll cut it. By the way, when I worked in our die shop I got to spend a lot of time with a Kellenberger grinder. It only had a three jaw chuck. It could be fine tuned with four adjustment screws. Very slick. Much easier to control jaw pressure and still fine set the job.
03-08-2007, 09:29 PM
We've come a long way from burnin' our fingerprints off from rubbing rings on sandpaper, eh?
03-08-2007, 09:41 PM
If the rings are held properly the fingerprints will stay intact.:D :D :D
03-09-2007, 06:00 AM
I'm bein friendly, honest....
Sanding rings has the disadvantage of removing the Parkerizing. Take that away, and you remove not only corrosion protection, but start-up lube as well.
Cotten and I never throw right crosses at each other. Maybe a left jab here and there but never a right cross. ;)
You just have to replace the parkerizing Cotten.
Yeah, I have seen those adjustable three jaws. Never used one though.
I mentioned TIRS because having all those dialed in, represents the original machining proceedure. When you have it all dialed in, you know exactly where the lands stand in relationship to the rest of the machine work. Hopefully they all run true enough to each other. Can't tell you how many times I have found otherwise on parts throughout my life span. This provides you with stock options such as what land to skin cut. how much to skin each land, and where the cut will be at the bottom of each land.
Kojack.... ever use a cathead ? We used to make these up for the tailstock end when re machining old roll shafts who's centers were either never put in or were beyond use from damage. They are hollowed out round stock [like unto a cap] with a center in the un opened end. The center was used with a live center in the tailstock. The other end of the cathead [cap] wall was drilled and tapped in eight equally spaced places around the circumference. The drilled and tapped holes held adjustment bolts for indicating the tailstock end of the roll shaft in. Used mainly for bearing journal work and many times body work as well. The combination of the cathead and a four jaw allowed you to dial a roll shaft in any which way you needed or wanted to. Paps
03-09-2007, 12:44 PM
Used a lot of catheads and always wondered how they got the name. Someone must have had a really ugly cat. I also made up a few "spiders" that would adjust to fit inside a thin walled job and allow you to chuck it with squashing it out of round. One of my regular assignments was making ladle car axles, kind of like a 20' long railroad car axle. I'd use a cathead to set the stock (which was always bowed) and cut spots for the two steady rests I had, then drill centers. Then I'd start roughing, turn the job around, rough some more, then have to re-cut the spots. The stock would bow in a different direction as it was cut and the stresses changed. Sometimes it would cause the bed of the lathe to start flexing as it changed. Usually took me 5-6 shifts to do one in the CNC lathe I ran. Of course none of this has anything to do with 45 pistons. Maybe we ought to start a "Dumb Machinists' Tips" section in the forum.
Dumb machinists topic.........great idea Kojack ! Should be fun, informative and interesting, to say the least. What do you think Cotten ? We could all learn a lot from each other experiences, such as, tricks of the trade, short cuts, eventful moments doing such work, even shoot the bull stuff. Share photos too ! Please do ! Paps
Used spiders too. Man Bro !! You bring back memories for me ! Your last reply reminded me of numerous such times. How does that song go ??? "THOSE WERE THE DAYS "
03-09-2007, 09:22 PM
I'm not a machinist, I'm a metal butcher.
So 'dumb machinist's tips' is right up my dumpster alley.
03-10-2007, 08:49 AM
I worked for a race engine builder many years ago and Cotten's method of holding pistons is very similar to what we did. However, instead of a face plate, I used a lump of Aluminum with a hole through the center for the draw bar. I chucked on the lump and would take a light face cut with each new job so I knew the face was true. Even though I learned a lot of useful car stuff at that place, it cured me of ever wanting a hot rod or doing anything more than changing spark plugs or oil on a car. It's funny how car people and motorcycle people really don't mix. A philosophical loggerhead.
Great tool Eric ! Along with lathe chucking and face plate usage. we now have three methods of doing the job of ring groove cutting.
Metal Butcher......:) Boy do I have stories on that !! Paps
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