45 Piston Rings Clearance

[Rex]

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?

[Paps]

Bore clearance or piston ring land clearance ? Paps

[Rex]

The ring grooves aren't wide enough, or the rings are too thick. (vertical measurement).

[Paps]

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

[Ohio-Rider]

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

[Rex]

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?

Rex

[charlie frey]

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.

[Rex]

Charlie-

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.

Rex

[charlie frey]

Originally posted by Rex
Charlie-
When doing this, how do you know when you're done?
www.aircooled.net.

Rex

Trial and error, my good man!
Slip it on the piston every now and then and use a feeler gauge.

[Paps]

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

[Kojack]

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.

[Paps]

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

[Rex]

Everyone-

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?

Rex

[cheifrider]

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 )

[cheifrider]

ps , its still running 6500 miles later