RCMK Engine Modification

Noph Veluvan created the topic: RCMK Engine Modification

This thread discusses the Content article: RCMK Engine Modification

Scott,
Thank you very...very..much for this article. My friends at the lake and I appreciate all your works.:)
#6380

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CrushKrew replied the topic: Re:RCMK Engine Modification

Great Article.....question: how do these mods compare to the ST cylider mods?? I have one and am wonderin.....:?
#6599

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Scott replied the topic: Re:RCMK Engine Modification

CrushKrew wrote:

Great Article.....question: how do these mods compare to the ST cylider mods?? I have one and am wonderin.....:?


RCMK's "Tough Racing" mods are pretty radical and do raise the performance over stock a bunch.
The way in which the factory modified the cylinder is by no means done in an optimal way. The HUGE eyebrow mods have created greater area than the transfer passage feeding the port, so flow control and exit speed of the out flowing air/fuel is compromised. No attention is payed to the blending in of the eyebrow cut to vertical transfer passage, so major turbulence has been created there too. As well by having any port, exhaust included having a wide flat roof profile aggravates ring clipping issues.

These "How Too" mods have shown to create equal if not slightly more horse power with an even broader powerband.
*Best thing being these mods you can do yourself without paying $200 or so for the modified cylinder kit.

In the end, just another tool in an RC boaters arsenal to have a little more punch and alternative set up to out run his competition :fencing:

2 stroke Engine Tech of 30+ years, Prop tweeker, Chronic tinkerholic, Home of Motor Heads RC Racing Engines ...
8 time NAMBA National 6 lap heat racing record holder.
#6601

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CrushKrew replied the topic: Re:RCMK Engine Modification

thanks Scott...I have read and re-read this article...holding the ST in my hand no less...:laugh:

I see what you mean about the radical eyebrows and the lack of "finish" blending....

I am going to apply what you reviewed to the ST and do some clean-up and see what I get...I have it already after all...

I have carefully looked at the EX port and it looks like they are now doing a arched roof like you show (this is a "new" ST)

as for the intake port...they raise the timing by cutting a small shelf...could use blending...so I will leave the piston alone...

I also have a full circle "stuffed" CY crank that fits perfectly...same crank that I fitted into my buddies QD25 (with a little lathe work on the diameter)...with good results...

do you have thoughts on using this crank with this motor??

Thanks Again...JC
#6604

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Scott replied the topic: Re:RCMK Engine Modification

In the FC crank Zenoahs I did a few years ago, you COULD NOT increase the intake duration very much, doing so only resulted in excessive spit back and an unstable high needle mix. Not a carb issue, but one of the engine spitting out so much air/fuel the engine has to re-breath it upsetting the mixture.

In the case of a Modified cylinder that has the intake duration altered within intake port and NOT the piston, would stick with a stock crank.

JMO tho :dance2:

Try it and see how bad it spits fuel out, worse case you install the stock crank :dash:

2 stroke Engine Tech of 30+ years, Prop tweeker, Chronic tinkerholic, Home of Motor Heads RC Racing Engines ...
8 time NAMBA National 6 lap heat racing record holder.
#6613

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CrushKrew replied the topic: Re:RCMK Engine Modification

thanks for the input...I will set up the otor and run it on my breakin boat b4 I intall in dragcat...

will try the stuffed crank and then if it has issues will install the stock crank knifedged like you did...in any even...will let you know how it goes...:drinks:
#6615

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Riggerman replied the topic: Re:RCMK Engine Modification

Great article as always Scott:drinks: Can't wait to get one and try the mods out.
#6659

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Bill Domingue replied the topic: Re:RCMK Engine Modification

Scott
I have done a mod as to your artical and would like to know what is use to finish the port after modding with the tool. Some of the mods I have seen done have no tool marking when completed. Please advise as to what to use
Thanks
Bill
#7354

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Scott replied the topic: Re:RCMK Engine Modification

For one, cutters used are "Single Cut" that leave little to no chatter marks. By gently overlapping cuts by the various cutters the profile of the modified ports takes on a very blended and smooth profile.

* Final smoothing is done using "CRATEX" points or spiral wound sand paper cones.
Down in the tight spots and near critical angles ONLY use the cratex points.

See: www.cratex.com/rubpoint.htm
Use FINE grit ( Red/brown ) in a HARD or standard bond #8 bullet

2 stroke Engine Tech of 30+ years, Prop tweeker, Chronic tinkerholic, Home of Motor Heads RC Racing Engines ...
8 time NAMBA National 6 lap heat racing record holder.
#7365

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kriscros replied the topic: Re:RCMK Engine Modification

is there anyone out there i could send a rcmk to, to get the mods done? I dont have it yet, just asking
#7597

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