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Author Topic: Longboy's "BEST FRIEND FOUR" model gas engine.  (Read 8182 times)

Offline Longboy

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Longboy's "BEST FRIEND FOUR" rod & piston.
« Reply #15 on: April 05, 2017, 05:48:30 PM »
The very basic barrel piston and a plain shape connecting rod fabbed from 1/4x 3/4 aluminum bar. I don't find Viton O- rings in my size at Ace Hardware. A plumbers O-ring made from....black stretchy stuff, makes the seal.



A pair of R144ZZ bearings ride in the small end. In a tutorial by Brian Rupnow, he mentions aluminum con rods can be their own bearing riding on the crankshaft throws. This would allow narrower 1/4 in. bar stock to be used. BEST FRIEND uses 3/16 in. throw pins and the 3/4 in. wide stock can also run on 1/4 in. pins using 4-40 rod cap bolts.


« Last Edit: April 18, 2018, 08:54:58 AM by Longboy »
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Offline Longboy

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Longboy's "BEST FRIEND FOUR" valvetrain.
« Reply #16 on: April 06, 2017, 08:37:12 PM »
On each side of the cylinder head will be the valve blocks mounted in outrigger fashion. On the ex. side, a strip of painters tape on each block face, some RTV sealant and eight ss 3-48 screws hold it together. The exhaust block is 9/16 in. wide and the valve guides are 3/8 in. and it was difficult putting on the RTV around the guide without contaminating the valve head or guide face tightening the screws down.  After about 3-4 tries, it was leakage free.



On the intake side, I tried furnace tape on the faces.....it was too thin. I went to some .060 gasket paper with RTV.......still leaks.  :disappointed: The gasket paper would get saturated with fuel and on compression stroke, would foam out between the two pieces! Not much margin here either from valve guide to edge of bar stock....and the screws are tightened.  Would have to find sheet rubber gasketing, remake using wider bar stock.....or sum-tin else. :headscratch:


« Last Edit: April 18, 2018, 09:00:48 AM by Longboy »
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Offline Longboy

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Longboy's "BEST FRIEND FOUR" valvetrain.
« Reply #17 on: April 08, 2017, 12:53:57 AM »
The valves are stainless in brass guides and the block has enough room for my solution.



Some 1/2 x 3/8 in. O-rings will have enough support on the block! :)
The guides were removed and a seat around their perimeter was cut in for them...



..and they leak no more! ^-^
« Last Edit: April 18, 2018, 08:11:32 PM by Longboy »
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Offline Longboy

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Longboy's "BEST FRIEND FOUR" valvetrain.
« Reply #18 on: April 09, 2017, 12:01:29 AM »
Another area that has to be leak free is the porting between the cyl. head and valve blocks. The brass tubing is blue Loctite in head but I want the valve blocks removable from head.



A set of eight collars for both valve blocks were made with O-rings to slip over the tubes. Three 6-32 bolts draw the blocks up to the head against the collars for the seal. The tubes do not penetrate the valve block port too deeply, the valve guides are close to the edge of block.

A side note with this valve arrangement is the porting volume, from cylinder to valves, becomes part of the combustion chamber volume for figuring the compression ratio. In BEST FRIEND, that would be 2 inches of 3/16 in. diameter porting between cylinder and valve guide per cylinder or .901cc.......ah, just forget I mentioned it. :Lol:
« Last Edit: April 18, 2018, 09:06:25 AM by Longboy »
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Offline Zephyrin

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Re: Longboy's "BEST FRIEND FOUR" model gas engine.
« Reply #19 on: April 09, 2017, 10:28:59 AM »
Quote
I find that the Kohler points has extraordinary stiff spring pressure for model engines...

I dont know for this type of points, but I agree that all commercial points I have found are all very stiff. However, in my last engine, a 8 cm3 mono 4 cycle , with a contact breaker from a moped, it worked perfectly without modifications, contrary to the many homeshop made points i did, with too weak spring giving lots of misfiring...

A great thread to follow, thanks to share.
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Offline Longboy

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Re: Longboy's "BEST FRIEND FOUR" model gas engine.
« Reply #20 on: April 09, 2017, 03:52:49 PM »
Quote from: Zephyrin on April 09, 2017, 10:28:59 AM
Quote
I find that the Kohler points has extraordinary stiff spring pressure for model engines...

I dont know for this type of points, but I agree that all commercial points I have found are all very stiff....

A great thread to follow, thanks to share.

Thanks Zephyrin. I've been using these Tecumseh points set on my engines and will continue. Pretty compact, they tuck up around the cam trigger and the spring tension is right. Part # 30547.

« Last Edit: April 18, 2018, 09:10:35 AM by Longboy »
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Offline Longboy

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Longboy's "BEST FRIEND FOUR" camshaft.
« Reply #21 on: April 10, 2017, 09:09:58 PM »
The cam drive is a pair of 20/40 MXL sprockets using a .25 in. belt. There are tooth belt calculators to determine the number of teeth needed for your set-up. I use this one!
http://www.bbman.com/belt-length-calculator/.



The cams just keep getting smaller! I'm using a 1/8 in. ss shafting with 5/16 in. cr lobes. This is the smallest I can manage for cam making stock.
Easy to hand file the profile after a couple passes under the mill creating the ramps. 4-40 set screws lock the lobes to shaft.



The lobe shows plenty of lift at around .085 in.




« Last Edit: April 18, 2018, 11:20:56 PM by Longboy »
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Offline Longboy

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Longboy's "BEST FRIEND FOUR" valvetrain.
« Reply #22 on: April 12, 2017, 04:11:39 PM »
The bucket lifters are threaded to the valve stems and evened out to same level. Valve lash is covered then by moving the camshaft up to the lobes, the mounting brackets for cam are slotted.
Initially the shaft would flex on valve spring compression, the span between bearings is over 5 inches. The ex. valve springs here were rewound using .020 piano wire to eliminate that issue, the .025 wire used too stiff. Another solution would be an added center shaft bearing.......but the Budget Dept. memo'ed back that there was no funding for that. :shrug:



A distributor cap base and sprocket guard are mounted to the camshaft brackets using a pair of 3-48 ss screws. R144 ZZ bearings support the shaft in the brackets.



« Last Edit: April 18, 2018, 11:18:52 PM by Longboy »
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Offline Longboy

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Longboy's "BEST FRIEND FOUR" In. & Ex. manifold.
« Reply #23 on: April 13, 2017, 05:41:27 PM »
A candy bar's worth of Delrin becomes the intake tract for BEST FRIEND. Is the best material here since mankind crushed rocks to make aluminum. :)  The cyl. head sculpted now.



A 1/8 in. brass modified plumbing elbow mounts the OS carb on top of pendulum. I really didn't care for the carb right angle stick-out. What to do..... :thinking:



« Last Edit: April 18, 2018, 09:25:19 AM by Longboy »
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Offline Longboy

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Longboy's "BEST FRIEND FOUR" In. & Ex. manifold.
« Reply #24 on: April 15, 2017, 08:06:02 AM »
Turning the carb 90 degrees and swinging it over the intake gives a better integrated look. The fuel metering needle screw now over its top and the fuel line will tuck in between manifold and valve block. :ThumbsUp:



The finalized intake was trimmed to width then. It is just a thumb press fit over the valve block port tubing.



The exhaust pipes come into the ex. valve block at an angle. I want to assure the forum that only the best quality steel shafting..... ever to be found in a Korean made VCR..... was used in their development! :Lol:



This is BEST FRIEND FOUR's story.  Coming next will be the studio photos and the running reveal.  :popcorn:  See you there! :DrinkPint:   Dave




« Last Edit: April 18, 2018, 09:29:23 AM by Longboy »
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Offline Jo

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Re: Longboy's "BEST FRIEND FOUR" model gas engine.
« Reply #25 on: April 15, 2017, 10:17:17 AM »
 8) looking forward to hearing her go Vroom, vroom.

Jo
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Offline Longboy

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Longboy's "BEST FRIEND FOUR" premier.
« Reply #26 on: April 16, 2017, 07:41:28 AM »
Welcome to my presentation of the BEST FRIEND FOUR flathead engine. :whoohoo:



The block and cylinder head were started back in July.



Work was set aside for the cooler days of Fall & Winter then.


Completed in February.



Being different with outrigger valve blocks. :o



And re-purposing electronics items for engine radiators.   :thinking:




And now....see how to burn a bottle of Coleman Camp Fuel in four easy cylinders! :drinking-41:   Thanks for following along!     Dave.

<a href="https://www.youtube.com/watch?v=2bRFujsk8LU" target="_blank">http://www.youtube.com/watch?v=2bRFujsk8LU</a>

« Last Edit: April 18, 2018, 08:23:07 PM by Longboy »
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Offline Admiral_dk

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Re: Longboy's "BEST FRIEND FOUR" model gas engine.
« Reply #27 on: April 16, 2017, 12:06:57 PM »
Nice engine and a very easy starter  :praise2:
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Offline Flyboy Jim

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Re: Longboy's "BEST FRIEND FOUR" model gas engine.
« Reply #28 on: April 16, 2017, 02:52:06 PM »
Fantastic!  :ThumbsUp: I love how the moving parts are out there in full view.

Jim
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Offline vcutajar

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Re: Longboy's "BEST FRIEND FOUR" model gas engine.
« Reply #29 on: April 16, 2017, 03:20:58 PM »
Congratulations.  A great runner.

Vince
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