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Running In New Piston Rings

A review of correspondence from NOC-L

The relative merits of running in new piston rings by the 'dry' method


Can new rings be run in dry?

A while back on Brit Iron, there was some discussion on the appropriate surface finish to use on cylinder barrels when installing new (cast iron) rings. I've always specified using a 220 grit hone for the final finish. However, the proponents of modern thinking now prefer to go with a fine finish (up to 600 grit), and build the engine with no oil on the rings to accelerate seating. It seems hard for me to accept; would anyone care to express opinions on actual results achieved ... either pro or con?

Greg Kricorissian (grkricor@ccs.carleton.ca) on NOC-L 8th. Apr 1997


Dry running in - a recommendation

I use a Sunnen AN 200 stone for cast iron rings and a AN 300 for ring sets with a chrome plated top ring. I've never been accused of modern thinking, but I do put the pistons in dry; I've never scuffed a piston and oil control has been good on most of the engines. I also don't break them in. As soon as the engine is warm enough to respond to throttle, it's gas it down the road.

As a matter of fact aircraft engine manufacturers say at least 75% power for the first few hours. The combustion pressure holds the rings out against the cylinder wall and for good seating they want lots of pressure, so that means lots of throttle.

Vernon Fueston (fueston@snowcrest.net) on NOC-L 9th. Apr 1997


Dry running in - other references recommending it as a method

This is quite well explained by Kevin Cameron in the March or April Cycle World. It seems that modern oils lubricate too well for break-in as we knew and loved it to occur. Thus, building the motor closer to the desired end result of perfect fit is required. The dry rings assembly was made famous by Udo Geitl in the mid 1970s, on the American Superbike championship winning BMW R90s that were BMW's swan song in racing. With instant and perfect break-in, and the best possible ring sealing, I've been doing it for 20 years with good results.

Who recalls Hepolite Powermax pistons, the principal feature of which was 'caragraph' coated rings? - a reddish coating that one was warned not to disturb, that supposedly enhanced break-in. Did it really work? Is it still offered?

Ben English (ben.english@dmvms.mailnet.state.ny.us) on NOC-L 9th. Apr 1997


Dry running in - another recommendation

I've used coarser grit with better results myself, I must admit. Fine honing was done when the bike reached rebore time (105,000 miles and still going strong) and the bedding-in did seem to take longer. When I was an agricultural engineer we used to work on compression-ignition diesels (between 22 and 25:1 compression ratios) and again, we used coarser grits (simply because that was what we used). There were no problems, and those engines needed to seat-in well and quickly, since they received very little maintenance and couldn't be let to burn too much oil when running.

As for dry assembly, well this is what I've always done, except on motors with splash-lubricated cylinder walls. How long the rings stay dry in an engine with active lubrication of the bores is open to question anyway. Whether they run dry at all, when kickstarting a newly rebuilt engine, with cold pistons with brand new rings and spray-lubrication of the bores, probably depends on how many kicks it takes to get the thing started in the first place. One thing I do, is to use a multigrade for the first half of break-in time, then switch to monograde. Multigrade oil is thinner on start-up and kinder on the new engine parts and I guess that since you're using the bike at run-in speeds you probably wouldn't need the better heat dissipation qualities that a good monograde gives you.

D.J. Walker (djw12@leicester.ac.uk) on NOC-L 10th. Apr 1997


Dry running in - better results than when oil was used

Three of the last four engines I've put new rings in have taken in excess of 1,000 miles to seat the rings, with oil fouling of the plugs a problem at low and moderate speeds. I've used the traditional method of 300 grit hone and assembly lube on the pistons and rings. The fourth engine, a 750 Atlas was done with a fine hone and no oil on the rings or cylinders. The rings seated immediately with no oil fouling. Still, I took it easy on the motor for the first while. I also used Castrol 20/50 as the break-in oil.

Thomas H. Allen (thomasa@halcyon.com) on NOC-L 11th. Apr 1997


Dry running in - further details

All I know about Mr. Geitl is what I've read on the Brit-Iron list. C.R. Axtell is my mentor on internal combustion engines. He taught me to put them together dry and it has served me well. After honing the cylinder I wipe the grit off with paper towels, then scrub the cylinder with waterless hand soap and paper towels until the towels come out clean. Then wash with solvent and blow dry with compressed air. The piston and rings go in absolutely dry but the rest of the engine is lubricated with oil or Lubriplate. I have used this method for over 20 years on car, motorcycle, and aircraft engines with good results.

Vernon Fueston (fueston@snowcrest.net) on NOC-L 11th. Apr 1997


A running in procedure

Before doing anything drastic, try giving the bike a good long ride with SA oil (the ultra-cheap non-detergent, non-additive stuff sold for old junkers). Since it has nothing to make it slipperier, it will give the rings a better chance to seat.

Also, make it a long ride of 100 miles or more on a highway, doing the following: accelerate quickly from about 35 to 55, let off the gas until it returns to 35, then repeat, over and over again; (best if the road is one with light traffic!) You can also do it at 40 to 60, etc., if minimum speeds are a problem, and as the rings break in, you could do it at higher speeds -- 55 to 75, etc.

Using this oil and this procedure, I have seated (cast iron) rings on Commando barrels without honing at all.

Mike Taglieri (miketnyc@juno.com) on NOC-L 22nd. Jun 1999

 

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