CMB RS91H ENGINE

[Jim Allen]

Bill Wisneuiski once showed me an engine that was running under a load on a test stand. He then put a stobe light on it and I could not believe what I saw. The engine was flexing and moving in ways that you thought would be impossible and still run without coming apart. :blink:

Charles, I have done these tests with my Strobette Model 964 stroboscope at night as a result of conversations with Bill Wisniewski & Henry Nelson. This is one reason I use a bar stock case & a hardened steel front end. I even screwed & bolted front ends to the crankcase in an attempt to stabilize this area. The extra lugs used by many speed flyers & tether car racers are the best solution to this problem. Also the use of one piece crankcases are some help in correcting this problem.

To keep things as round & stable as possible in the critical upper areas of the liner during long heated runs at full throttle, I have found the following to work very well. Keep the liner wall thicknes at a minimum of .100; increase the lip thickness to .200, with the piston traveling half this thicknes when at top dead center; increase the diameter of the lip to the maxium diameter possible; put the head bolts through the lip, not outside the lip; use 8 bolts to hold the head, the liner & the motor together as one unit. These things have been in use by many foreign tether car racers on large & small engines for several years now. Examination of wear patterns after extensive dyno pulls indicate these changes are working.

I have posted pictures & explanations under piston relief areas.

Jim

 

[Charles Perdue]

Mr. Jim, I am still up for adoption so you can teach me all of your speed secrets. Wasn't one of your engines blocks made of steel? Did you see any differences as far as stability by using this material? Any advantages or disadvantages other than weight? Curious.

 

[Jim Allen]

Mr. Jim, I am still up for adoption so you can teach me all of your speed secrets. Wasn't one of your engines blocks made of steel? Did you see any differences as far as stability by using this material? Any advantages or disadvantages other than weight? Curious.

Charles, I will not adopt you & stop calling me Mr. Jim. There are really no speed secrets, only very sound engineering & many hours of bench testing. Does anyone think that the builders of high performance motor cycles, race cars, racing outboards or inborards run these engines before testing them on a dyno? Even the sanitation department of New York City has two dyno's to test rebuilt diesel engines.

Using the strobe while running that steel crankcase (made of 12L14 ledloy steel) in the darkness showed me that all of those engine oscillations could be eliminated. Helping this, was the use of a hardened steel front end & a very rigid mounting. The main advantages were a substantial HP increase (no information to be given); greatly decreased vibration & extended bearing wear every where in the engine. The main disadvantage was the weight!

Jim

 

[Rick Doane]

"I could feel the carb, the lower part of the engine case and they would be cool, sometimes very cool."

Charles....I have had the same thing occur with one of the old Picco .65 w/the black carb. The only difference was it would do this in the boat while running. When I would bring it in, the carb would be extremely cold even to the point of frost on the body.

Jim.......I use to have access to an x-ray machine to examine aluminum for high and low density spots within the metal. You would be surprised how much "unusable" metal is in raw stock depending on what you want to do with it, especially when heat cycling is involved.

Rick

 

[Jim Allen]

"I could feel the carb, the lower part of the engine case and they would be cool, sometimes very cool."

Charles....I have had the same thing occur with one of the old Picco .65 w/the black carb. The only difference was it would do this in the boat while running. When I would bring it in, the carb would be extremely cold even to the point of frost on the body.

Jim.......I use to have access to an x-ray machine to examine aluminum for high and low density spots within the metal. You would be surprised how much "unusable" metal is in raw stock depending on what you want to do with it, especially when heat cycling is involved.

Rick

Rick, this can be a problem with cast and continous cast alloys used for pistons. The newer meltspinning, chopping, compaction, extrusion process seems to have eliminated this.

Jim

 

[F.Orlic]

Mr. Jim, I am still up for adoption so you can teach me all of your speed secrets. Wasn't one of your engines blocks made of steel? Did you see any differences as far as stability by using this material? Any advantages or disadvantages other than weight? Curious.

Charles, I will not adopt you & stop calling me Mr. Jim. There are really no speed secrets, only very sound engineering & many hours of bench testing. Does anyone think that the builders of high performance motor cycles, race cars, racing outboards or inborards run these engines before testing them on a dyno? Even the sanitation department of New York City has two dyno's to test rebuilt diesel engines.

Using the strobe while running that steel crankcase (made of 12L14 ledloy steel) in the darkness showed me that all of those engine oscillations could be eliminated. Helping this, was the use of a hardened steel front end & a very rigid mounting. The main advantages were a substantial HP increase (no information to be given); greatly decreased vibration & extended bearing wear every where in the engine. The main disadvantage was the weight!

Jim

Dyno is a good thing and one can learn a lot from it but when engine is ran on dyno we control many things ;constant load, temperature, vibrations, drag etc. Running on water things are everything but controled. As I've said before what you see on dyno might or might not work on water.

One of main reasons for cases flexing is soft cast, billet aluminum is much stronger and there are some great aloys available. When engine manufactors started to make one piece cases engines also became much more reliable and longer lasting.

 

[Charles Perdue]

Mr. Allen, what are your thoughts on whether the sleeve remains tapered under operating conditions as when the top of the engine is hot and the bottom of the engine is much cooler or does it straighten out due to the differences in the expansion of the material in the sleeve from the top to the bottom? :huh:

 

[Jim Allen]

Mr. Allen, what are your thoughts on whether the sleeve remains tapered under operating conditions as when the top of the engine is hot and the bottom of the engine is much cooler or does it straighten out due to the differences in the expansion of the material in the sleeve from the top to the bottom? :huh:

Charles, I think in a setup like mine the taper remains because of the way the top end is made. I don't know for sure how much, if any taper is lost under runing conditions due to the heat in the upper end.

Since the heat is applied to both the piston & the liner the fit should remain the same.

Jim

 

[Tim_Duggan]

I don't know for sure how much, if any taper is lost under runing conditions due to the heat in the upper end.

Since the heat is applied to both the piston & the liner the fit should remain the same.

Jim

Jim,

Wouldn't that depend on the thermal expansion rates of the piston and the liner being similar, if not the same?

Tim.

P.S - you might want to change the wristpin in that new K90 you mentioned earlier for good measure!

 

[Jim Allen]

I don't know for sure how much, if any taper is lost under runing conditions due to the heat in the upper end.

Since the heat is applied to both the piston & the liner the fit should remain the same.

Jim

Jim,

Wouldn't that depend on the thermal expansion rates of the piston and the liner being similar, if not the same?

Tim.

P.S - you might want to change the wristpin in that new K90 you mentioned earlier for good measure!

Thats correct Tim. This is why high silicon aluminum pistons (30%), (8.3micro in/in/deg F thermal expansion), should not be used in #360 brass liners (11.4micro in/in/deg F thermal expansion). A better material would be #544 phosphor bronze (9.6micro in/in/deg F thermal expansion). The addition of the hard chrome plating lowers the the thermal expansion of both alloys. Also the #544 material has a higher tensile & yield strength. It is also harder than #360 brass, but #544 is much more expensive.

I puschased the K90 motor only for inspection purposes.

Jim

 

[Tim_Duggan]

Jim,

If 30% is not considered desirable - What % silicon alloy would be more suitable for chrome plated #360 brass liners based on thermal expansion rates? (I'm assuming this reference is for commercially available liners)

Also - while on the subject, how do chrome plated aluminium liners with 30% Si pistons compare? I'd imagine they are considerably different to brass.

Very interesting subject B) I have a liner being fitted with a new billet piston as we speak - for a K82.

Tim.

 

[Buckshot]

Sorry to interrupt class, but how dose the new CMB RS91H compare in weight to say a MAC .84?

-Buck-

 

[Jim Allen]

Sorry to interrupt class, but how dose the new CMB RS91H compare in weight to say a MAC .84?

-Buck-

Buck,

The MAC .84 weighs 1lb 11ounces with the flywheel & the CMB 2lbs 9ounces. Interesting note; the Mac .84 is lighter in weight than the Mac .67 which weighs 1lb 14 ounces.

Jim

 

[Buckshot]

Thanks Jim.

-Buck- B)

 

[Jim Allen]

Jim,

If 30% is not considered desirable - What % silicon alloy would be more suitable for chrome plated #360 brass liners based on thermal expansion rates? (I'm assuming this reference is for commercially available liners)

Also - while on the subject, how do chrome plated aluminium liners with 30% Si pistons compare? I'd imagine they are considerably different to brass.

Very interesting subject B) I have a liner being fitted with a new billet piston as we speak - for a K82.

Tim.

Tim,

Mahle #138 with 18% silicon & a thermal expansion rate of 11.1 micro in/in/deg F works very well in all the test I have done. I do not know what is used in commercial motors for liner material, probably what ever is cheap & available. #360 free machining brass is both of these.

30% silicon aluminum pistons work very well with silicon aluminum liners made of Mahle #138 or RSP #446 (20%silicon). In the early days the standard aluminum casting alloy A357 (7% silicon), was used for aluminum liners. The problem with chroming aluminum is the high rejection rate that comes about even when cleaning carefully. The areas where the chrome flakes off show up during grinding. Since the chrome can not be removed with a 50% solution of HCL acid, these parts become scrap. This is why I use brass or bronze.

Many different things can be made to work if the engine is fitted correctly when it is cold.

Jim

 

[Dan_Cousin]

Jim,

are the piston and sleeve at the same temperature? if the piston is significantly hotter, would it dictate a low TCE material so it doesnt' outgrow the bore. How does the expansion of the aluminum case affect this TCE matching exercise?

Very interesting subject by the way.

P.S. I noticed you have a 7HP custom engine in your photo gallary. How much HP did you get with a stock 90 motor. Back in the day everyone was claiming 5HP and the target to beat for 90s.

 

[Jim Allen]

Jim,

are the piston and sleeve at the same temperature? if the piston is significantly hotter, would it dictate a low TCE material so it doesnt' outgrow the bore. How does the expansion of the aluminum case affect this TCE matching exercise?

Very interesting subject by the way.

P.S. I noticed you have a 7HP custom engine in your photo gallary. How much HP did you get with a stock 90 motor. Back in the day everyone was claiming 5HP and the target to beat for 90s.

I don't know if the piston & sleeve are the same temperature, but they probably are not. I think this is why lower expansion alloys must be used for pistons & higher expansion alloys for liners. The information I have from MALHE GMBH does not address electrical temperature measurements of liner walls. This is because the piston is not in direct contact with the liner except in the TDC area in unringed motors & only through the piston rings in ringed motors. I don't know for sure, but I would think, the very low expansion of the upper aluminum or steel crankcase area has very little, if any, effect on the TCE matching exersize. A very thick & large lip diameter fastened between the crankcase & head definitely have a positive effect on internal cooling is this area.

The only stock motor I have used & tested on the dyno was a highly modified 1978 yr, OPS 67. This motor on 65% nitro would produce 5.8 to 6.2 HP at 24,000 RPM. Every part in this motor was broken at some time, even the lip the liner sat on, in the crankcase, would be crushed. I have posted a picture under piston relief areas of the hard steel insert that was shrunk into the crankcase to prevent this.

Jim

 

[Charles Perdue]

My thoughts on the liner taper under running conditions. I believe that the taper of the liner pretty much goes away due to expansion from temperature differentials and pressure loading differences from the top of the sleeve to the bottom. I also believe that this contributes to some of our engines "staging". As the liner staightens there is less friction between the piston and the sleeve. This in combination with the pipe, the intake track, the porting, the port timing, the tuning, the engine temperature and a multitude of other variables is what allows our engines to "stage". When all of this comes together and the RPMs climb that is really sweet music. Just my opinion.

 

[Charles Perdue]

I am very interested in other engine builders thoughts. Come on Jack O'Donnell, don't be bashful. I know that you have done about as much in piston/liner and taper work as anyone. I really respect your opinions. Enlighten us with your vast knowledge.

 

[Jack ODonnell]

Hi Charley ; I will try to put something together on this subject. Regards J.ODonnell