Does anyone have pictures of what it takes to put a full circle crank in the Zenoah Case?

Bruce,

No pictures of doing one, but here is a CASE shot with one installed, other shot of the Modified flywheel and required adapter.

I run 2 Zenoah 260's with RC cranks, they both run really well ;D

** What is required in getting the RC crank into the 231/260 cases is :

#1 Grind down the outside diameter of cranks counter weights @ .040" .... OR,#2 Open the inside diameter of cases an equal amount :

** I choose to grind the O.D of cranks on both of mine.

The P.T.O. end of either crank is the same, BUT the mag side is shorter on the RC crank that requires modifying of the stock flywheel and a billet extension/start dog placed threw the middle of it.

BTW.
In using these RC crank adapters, you get adjustable timing capacity because the mounting holes are slotted :

Modified flywheels and adapters can be purchased from Robert Finn at: This email address is being protected from spambots. You need JavaScript enabled to view it.
Bob is out of TEXAS U.S.A.


Regards,
Scott http://www.modelgasboats.com/media/kunena/attachments/legacy/images/2671_260_mods_014_jpg1251d5f47076bfd621b6325417fb795e
http://www.modelgasboats.com/media/kunena/attachments/legacy/images/2673_260_mods_018_jpgafe5ee4884595d0c115b520dc427faab

We dynoed the same cylinder on a Zenoah PUM crankcase with the dog bone crank and an RC car crankcase with the full circle crank. To my surprise, we found no difference in power. The car crankcase was modified to use the small flywheel Zenoah ignition and I expected that it would be the next step up in Zenoah modifications.

Lohring Miller

Thanks for the pictures i see you flat top the piston.How does that help with the mod?

: Bruce,

In this specific 260 engine, the flat top piston is only a small part of the unique set up

Look closely and you will see HUGE vertical slots on either side of pin boss.

** If interested in seeing more photos of this Very Exotic 260 ? ... Let me know and I will post them.

This engine is what I use in my Blazer Whiplash, It is set up to run Super strong on upper mid to high rpm, the flat topped piston is done to actually reduce compression. Reason is that when running these engines at really high rpm under a light load with a really efficient tuned pipe installed the boost from pipe is SOOO strong engine runs better starting out with the lower compression.

Once the engine is turning up at around 17K + and boost from tuned pipe is maxed out, the actual captive compression engine is running at is QUITE a BIT higher than the static compression ratio.

This same set up using a domed piston does not rev out as well IMO.

** Been running this engine now for 2 Race seasons with out issue.
;D And actually Set a New NAMBA National 6 lap record with it at the Gold Rush race 2 weeks ago ;D

It is a pretty wild engine to say the least ...

Regards,
Scott

Sounds like a winner,great job.Does the Sikk crank have the same size as the full circle rc zenoah crank?The pictures of the super mod would be great.Thanks Scott for sharing your knowledge.

Yes, the CY "Sikk" crank is the same size as the Zenoah "RC". But .... Don't use the stuffed version like is stock on the Sikk 26 marine's, they will throw the stuffing material at high RPM !!

These same photos and build info were shared on JRCBD over 2 years ago and really never received much interest ... funny how whats so foreign in terms of whats being done, sometimes is the sleeper that really sets apart the average from the awesome.

The edges of transfer passages within cylinder have been adjusted too line up with outsides edges of the pistons cut out slots.

* Weight of this highly modified piston came in a tad under 21 grams *

My general idea was to use the lower case volume of the RC crank to place MOST of the case volume up into the transfer passages and under piston, the vent slots within piston make every possible volume of air/fuel flow capable of exiting cases into the cylinder.

Very stringent efforts were made in keeping port angles aimed properly on all transfer windows maintaining flow symmetry from both sides, this extra effort required because of so much flow volume available.
The flow of air/fuel that does travel threw the piston slots needed to be directed into transfer passages very smoothly so as not too upset the natural smooth flow path in them out to the exit window of the actual ports.

The last photo was taken just tonight after I took top end off the engine after 2 years use !! ... The burn pattern tells the story on air/fuel flow threw this engine ;D

Scott

http://www.modelgasboats.com/media/kunena/attachments/legacy/images/2675_260_mods_002_jpg3e07126606bbd195d06b9576336cf102
http://www.modelgasboats.com/media/kunena/attachments/legacy/images/2677_260_mods_010_jpgbce65af3785106b4314f86159566a20e
http://www.modelgasboats.com/media/kunena/attachments/legacy/images/2679_260_mods_015_jpgfa4af8aaad9089259c6624567e2a1a0e
http://www.modelgasboats.com/media/kunena/attachments/legacy/images/2681_260_mods_011_jpgc3b22db18544ec50a2f2234e6c36e3f3
http://www.modelgasboats.com/media/kunena/attachments/legacy/images/2683_Engines_X11_jpgc90b1110ce0b3981470eec006ea5a77b

Scott

Your engine builds are always interesting to me. The last picture shows a carbon pattern on the piston that I have just started looking at. I noticed that both your piston and the one from my M&D cast cylinder engine have a very crisp pattern. My favorite mod Zenoah piston's pattern is fuzzier. I wonder if this indicates better scavenging flow control and contributes to better power. The cast cylinder engine is second only to the 25cc Quickdraw in power on our dyno.

Lohring Miller

Lohring,

With such radical flow paths happening within a Schrule ported 2 stroke engine, along with the thermal dynamic cooling the air/fuel has on parts of the engine it flows over, One would think that even the slightest flow variance would have thermal repercussions of the combustion process to show up by the carbon trace left behind.
*Basically what we are seeing now.

Where the cooling flow of the air/fuel is nil, piston run slightly hotter along with not having the air/fuel flow sweeping away residual deposits after each combustion cycle.

The more even an outline of the carbon trace is, stronger the flow boundary is defined on where actual flow is going and to a degree how much directional disturbance is present.

This is why ALL truly Hi output 2 strokes use cylinders with full liners and very accurate positioned transfer dividers and controlled exit shape aiming the outflow of air/fuel into combustion chamber, along with accurate exhaust window shapes to control outflow and enhance pipe boost return.

JMHO Scott

Pretty deep stuff really :-

does the crank or case need to be modded as well to use a full circle crank in a QD case?