Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 129375 times)

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #135 on: January 11, 2015, 01:40:59 AM »
This photo gives a better idea of what the double roller assembly looks like before placing the connecting rod in position. There is approximately .001" to .002" total clearance in each window between the rollers & the cage.

JA

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #136 on: February 13, 2015, 02:25:19 PM »
Initial testing of the machined double roller retainer design has been successful thus far. The photos show the actual assembly still in the engine after several test runs at very high RPM's (19,000+).

Jim Allen

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #137 on: February 14, 2015, 02:34:28 AM »
Have just read the thread from beginning to end, absolutely amazing work Jim, and thanks for openly sharing such a wealth of knowledge!
I hope to be able to use your chrome plating guidance in future, assuming I can find a source for the various acids required. They are not so easy to obtain in the 'Nanny states' of Australia.
Many thanks.
Simon

"The reality is that without cheap imported machines, I would be spending my time doing something less creative and less enjoyable" - Captain Jerry

Offline Niels Abildgaard

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #138 on: February 14, 2015, 06:07:15 AM »
Hello Jim

I thougth You were using Cantilevered cranks only but the last three pictures is a normal pressed up construction?

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #139 on: February 14, 2015, 02:24:14 PM »
Hello Niels,

I have used both types of crankshafts in engines with different type induction systems. I have also used crankshafts with the induction passage machined in the crankshaft itself. There is an indication in smaller size engines that a cantilevered type crankshaft can produce more HP than an induction system (rotary valve, inverted & standard drum valves, bell valve) which would be driven by the crankshaft. The previous photos show an engine which uses piston porting for the induction process. This is the simplest induction system that can be used but it does not allow independent control of the induction's opening & closing events. The induction timing, which is controlled by the bottom of the pistons skirt, is symmetrical, with the opening & closing the same.

JA

Offline Niels Abildgaard

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #140 on: February 14, 2015, 03:01:25 PM »
Hello Jim.

This corresponds quite well with one of the brains behind the last 125 ccm engine (Frits is his firtst name)

http://www.pit-lane.biz/t5121p680-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-4

Somewhere in the very long thread he says that the ideal engine has a funny arrangement  for inlet control like bell,disc,piston port etc for starting and low load ,but when the going gets rough, a permanent open hole is best.You will have to register to see the pictures but the very friendly administrator speaks english and the two Aprilia gentlemen only write in english.

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #141 on: February 14, 2015, 03:05:35 PM »
I should apologize for skipping over many of the details of exactly how some of these pieces were made. In many instances there are no photos or prints, only the completed pieces & the fixtures used. Three piece crankshafts are machined .005" over size for OD's & .005" undersized for ID's. Grinding of OD's & ID' is done with fixtures such as shown in the photos. Assembly of the three piece crankshafts is done in a die set type fixture & then trued within .0002" in two axes from end to end, with each axis 180 degrees apart. The final truing is done with a four jaw independent chuck & .00005" indication. The crankshaft is zeroed in the chuck at is short end first before twisting & bending the end sticking out. A large, very rigid lathe spindle & a quality independent four jaw chuck make this possible.  I use this level of precision for three piece crankshafts because the engines where they are used have four main bearings, two on each side.

Jim Allen
« Last Edit: February 14, 2015, 05:10:42 PM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #142 on: February 14, 2015, 03:15:57 PM »
Hello Jim.

This corresponds quite well with one of the brains behind the last 125 ccm engine (Frits is his firtst name)

http://www.pit-lane.biz/t5121p680-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-4

Somewhere in the very long thread he says that the ideal engine has a funny arrangement  for inlet control like bell,disc,piston port etc for starting and low load ,but when the going gets rough, a permanent open hole is best.You will have to register to see the pictures but the very friendly administrator speaks english and the two Aprilia gentlemen only write in english.


I believe you are referring to Frits Overmars & Jan Thiel who are members of The Two Stroke Tech site. Both of these individuals, as well as individuals such as Darcy Rosenthaler, Lohring Miller & others have been invaluable in providing factual, in depth knowledge concerning every aspect of a high performance two cycle engine. There is an in depth discussion about the 24-7 engine theory on this site. I consider the site to be number one in the field of high performance engine building & tuning.

Jim Allen
« Last Edit: February 14, 2015, 03:34:08 PM by strictlybusiness1 »

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #143 on: February 14, 2015, 04:44:03 PM »
Jim, I think it's more that I've learned from you than you from me.  I mostly have off the wall ideas.  You put them into practice.  I'm glad you are finally addressing the connecting rod big end bearing problem in racing gas engines.  That's been a weak link since we were pushing Quickdraws to their rpm limit.  Even modified Zenoahs are seeing rod bearing failures as they run more and more over 20,000 rpm.  My only gas engine rod failure was a bearing cage failure.  This allowed the rollers to skew and the result is below.  Fortunately, the cylinder, an M&D cast unit, wasn't destroyed.

Lohring Miller

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #144 on: February 14, 2015, 04:59:59 PM »
Lohring,

The person who manufactures the OD engine has purchased some of the latest design retainers to test in his R/C gas cars & on his dyno. He wants to build OD top end assemblies (32 or maybe 34 cc) that could be used on Zenoah bottom ends. Of course the present Zenoah 32 cc bottom ends are failing with 20 ounces of oil/ gallon & engine RPM's of 16,000. This person is not aware of the necessary metallurgy or radial tolerances necessary to give a reliable bottom end assembly that can withstand 24,000+ RPM.

Jim Allen

note: I haven't forgotten about the mold, just cannot find enough time because of what is taking place at Aero Precision Machine concerning the greatly increased Nelson Q-40 production.
« Last Edit: February 14, 2015, 07:25:39 PM by strictlybusiness1 »

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #145 on: February 15, 2015, 06:48:45 PM »
We ran into two big end bearing/crankshaft problems in our testing.  Since we were going for straight line speed with existing propellers, top speed was directly related to rpm.  We could run Quickdraws to at least 25,000 rpm for a short time without failure.  They probably developed around 3 to 4 hp at this rpm.  They had a 28 mm stroke and 34 mm bore.  After they noticed big end bluing on their dyno, Quickdraw modified the rod bearing with oil slots and increased clearance.  We didn't experience any problems after that.  My engine, pictured in my last post, had several racing seasons of high rpm operation before failure.  The crankshaft and connecting rod was the stock Zenoah one, the same as Quickdraw used.

On the CMB, a 35 mm bore and stroke engine, we had issues with the crankshaft flexing as shown by flywheel strikes.  The solution was to add another bearing on the front of the crankshaft.  Other problems limited the rpm to around 23,000.   We never had a rod bearing issue so we didn't make any modifications or measurements.  I think crankshaft rigidity is as much of an issue as bearing design, though.

Lohring Miller

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #146 on: February 15, 2015, 07:13:17 PM »
I totally agree Lohring. There is only one way to prevent crankshaft flexing. Make the crankshaft larger in diameter, mine are 15 mm compared to the stock 12 mm size & make the dog bone a full disk type. Total elimination of roller skewing & limiting roller sliding to a minimum are the other things that would allow the engine's RPM to easily exceed 23,000 & very possibly go as high as 28,000. Increasing radial clearance amounts in roller type assemblies always encourages an increase in roller sliding. Roller sliding is also effected by roller OD finish & the crank pin's OD finish.

JA

note: Lohring, I have been informed that there should be some very encouraging information posted on JRCBD this evening after more wide open throttle testing. More than four 500 ml bags of fuel & no signs of any failures. This is just with a change of the retainers design & all other parts remaining stock including the radial clearance numbers.



« Last Edit: February 16, 2015, 01:56:38 PM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #147 on: March 09, 2015, 10:47:14 PM »
For the last month I have continued to investigate the possibilities of bottom end roller assemblies that would be used in 15 to 30 cc two cycle engines. These assemblies must be able to operate in the 22,000 to 28,000 RPM range, at 7.5 to 9.5 HP, with absolute mechanical reliability.

The tools shown in the first photo, as well as the holding fixture mounted onto the Brown & Sharp's solid tapered center, are required to machine the 14 slots in the retainers .5470" OD. The slots are 25.714* apart. A calculation is made of the width of the retainer's pie shaped piece between each .0787" wide slot, measured at the roller's center line. This dimension is approximately .027". The following calculation is made to determine which dividing plate is needed to give 14 divisions of 360*. Since the dividing head is geared 40 to 1, 40 is divided by 14 which equals 2 12/14 = 2 6/7 = 2 42/49. This means that for the indexing of 14 slots, each 25.714* apart, the dividing head is rotated 2 turns (18*) plus 42 holes (7.714*) on a 49 hole plate. The dividing head is rotated an additional 2 holes to give .001"+ clearance (.0797") for each roller in it's slot. Again the 40 to 1 gear ratio means that one complete rotation must equal 9*. Using a 49 hole plate means that each hole equals 9* divided by 49 or .1836* (11 minutes). Therefore, two holes on the 49 hole plate equals .3672* (22 minutes). This is sufficient to give the necessary .001"+ clearance in each slot.

The dividing head repeats accurately because there is no vernier scale to read. The spring loaded tapered pin must drop in it's hole for indexing amounts. The two photos before the last two show how easy it is to index & open the slot for the .001"+ clearance.

The last two photos show how the machined sleeve is mounted & located precisely for machining. By using a solid aluminum mandrel inside, which is located in the holding fixture, there are no burrs to be removed on the ID of the retainer after machining. Tumbling removes any burrs on the retainer's OD. The sample roller & the gauge pin act as go-no go gauges for slot measurements.

Jim Allen
« Last Edit: March 09, 2015, 10:50:48 PM by strictlybusiness1 »

Offline 90LX_Notch

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #148 on: March 10, 2015, 12:11:10 AM »
Jim-

I've been following this thread from the beginning.  The "full on" effort is beyond words.  High end competition is always about the details and your attention to details is amazing.  Thank you for the education and your willingness to share with us.

-Bob
Proud Member of MEM

My Engine Videos on YouTube-
http://www.youtube.com/user/Notch90usa/videos

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #149 on: April 05, 2015, 06:12:46 PM »
It should be noted that the building of very high RPM, high HP, connecting rods "CANNOT" be made to operate mechanically reliable without consideration of wrist pin, crank pin & crankshaft axis squareness. Keeping these axes square to each other can become difficult if not impossible without proper machining fixtures & jigs. Squareness of + or - .0002"/ 6" allows connecting rods to be built with .0001" radial clearance in the top end & .0003" radial clearance in the bottom end over a connecting rod center distance of 1.741".

The crankcases in the first photo are machined from aluminum alloys 2024 T-351 & 7075 T-651. Several crankcases were machined from 12 L 14 Leadloy steel & these were used for dyno testing only. Transfers are broached machined from the inside of the cylinder bores using a proprietary process. Different transfer shapes: number of transfers; entry angles, both axial & radial; as well as different depths were dyno tested. After many hours of testing, I can only say, without any doubt, that bigger area transfers DO NOT necessarily mean more HP. However, a steel crankcase runs faster than aluminum because of the greater rigidity of steel.

The bottom & rear of the fixture shown is square within .0001" over 6". When mounted to the machined face plate of the lathe, the cylinder bore & the front end bores can be machined square to one another. The face plate is mounted to the lathe's spindle with a D-4 camlock nose. Two .3752" dowel pin locations in the bottom & the rear of the fixture make precise re-location easy. The fixture is held securely to the lathe face plate with a custom made draw bar extension. Cylinder liner bores & crankshaft bores THAT ARE NOT SQUARE TO ONE ANOTHER produce all types of unsolvable mechanical problems, such as, connecting rod walking on the crank pin; cocking of the piston in it's bores; poor wear characteristics in bushed & roller type rods; high wear in piston boss holes; high friction & heat in associated parts; etc.

The four small diameter locating pins located on the top of the fixture, beneath the clamping devices, engage the four crankcase mounting holes with a tight fit. The engine begins as a block of metal with the mounting lugs already machined. It is clamped for all machining operations while in the fixture including the cylinder bore & face; the front end bores & face; the back end bore & face; 8-32 threaded holes for the front & back ends; 8-32 threaded holes for the head bolts; the exhaust outlet & the 8-32 threaded holes for the exhaust header; profiling of the crankcase outside & the internal broach cutting of the transfers.

More to come........................

Jim Allen
« Last Edit: April 05, 2015, 06:31:46 PM by strictlybusiness1 »

 

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