Would you like a new button

[Jerry Wyss]

Jerry? What would you charge me on working on the two BX-R thundertiger pro.21's??? I would like to have in all three motors done by you! One would be in a boat the other in the hotrod hydro and the third would be the back up motor/spaire. I'll send the M-R pro.21 in Oct or first week of Nov to you. Which is the better motor form TT?? The MX-R,M-R or the BX-R??? <_<

Well the BX-R is a pull-start buggy engine and I think your running these in a I/B, yes? The pull starts are a drag on the engine but that might not be a bad thing for a 26" boat, aren't they?

The MX-R must be a pullstart too, short stroke version, (stroke/bore of the engine I mean)

and M-R is a non-pullstart and short stroke (I think). The SS engines I would have to make a button for, the LS versions,

(BX-R)(B-R) I use another make of engines button, the rest of the mods are basicly the same for all 3.

It's best to have new piston&sleeve to do this so which ever one has that new P&S I would start there.

Reason I mention that is the TT P&S fit hasn't always been the best and can go away quickly if mistreated.

The BX-R seems to have a piston with a bit more silicon in it's construction, they have held up pretty well for me.

The other two, I don't know that much about cause most of my work has been on the PRO-21M-O/B ,

TT 21 BX-R buggy and a multitude of other make buggy engines for powerheads on the TT O/B lower.

I can give you figures in a "PM" along with my address and we'll just do one at a time if you want.

New CNC made buttons will be coming soon so if you want to wait for that it'll prolly be worth it, an cheaper too,,maybe

JW

 

[misshydro]

Jerry,just went to the thundertiger.com sight.The blocks,rods and pistion&cyclender set is the same! The out boards,Pro-21MX-R and Pro-21M-OR and the inboard Pro-21MX-R and Pro-21M-R ,cranks postion&cyclender,water&head bottons,rod are the same,But two different carbs numbers on outboard and inboard.The BX-R and the B-R(P),There blocks,rods pistion&cyclender sets are the same as the boats!! So why you said the BX are long stroke motor??Unless the crank stroke are different/longer throw??

 

[Jerry Wyss]

Jerry,just went to the thundertiger.com sight.The blocks,rods and pistion&cyclender set is the same! The out boards,Pro-21MX-R and Pro-21M-OR and the inboard Pro-21MX-R and Pro-21M-R ,cranks postion&cyclender,water&head bottons,rod are the same,But two different carbs numbers on outboard and inboard.The BX-R and the B-R(P),There blocks,rods pistion&cyclender sets are the same as the boats!! So why you said the BX are long stroke motor??Unless the crank storke are different/longer throw??

To keep it simple, the ones that list:

Bore- 16.6mm/ Stroke- 16mm are Short Stroke (SS)

Bore-16.26mm / Stroke-16.8mm are Long Stroke (LS)

The stroke is made in the crank throw

Also: The O.S.20J carb that comes on the O.S.21-XM O/B makes life much easier and fit's the "EVO" style TT case,

(BX-R and B-R) buggy case. I'll have to go to that Taiwan website to check out the "M" stuff.

JW

 

[Jerry Wyss]

I got to do something different lately,, a guy on here wanted me to hop-up his Thunder Tiger O/B but

it had to be run on 30% nitro. I haven't really done that before but modded it like I did the others.

.015" sleeve shim, crank 30* open - 65* closed, exhaust port to 178* and made a button with a

fairly broad flat squish w/.185cc volume, MC59 plug, O'Donnell 30%, cutdown P-215 on the L Y N X.

Yesterday (friday) zipped the needle open over a turn and 1/2 from where he had it, tossed in and

it wanted to take right off, back in quickly, zip, zip open some more, back in and ,there, now it's rich

enough,,, but, b, whats that "fish fryin' sound. Back in and Yeeoww! It's Hot! on the aircooled head,,

installed .006 headshim(now @ .014" H/S) , ran more normal but still came in more than hot enough.

Replaced MC59 with MC8 and over a couple runs it was haulin the mail, very fine running motor,

the owners going to be very happy.

The key thing is I learned something that I already knew but have never experienced it, lower nitro

does require more volume and less advanced plug timing. The engine didn't mangle either plug and

the piston/sleeve was in good shape for being so hot the couple brief times,,, now I just gotta figure

out what to do with the rest of this 30% :lol:

JW

 

[Jerry Wyss]

Im interested to see what you guys come up with for the XM. I have made quite a few buttons for it (air cooled and water cooled), but havent found anything better than the stock design. I have a bunch of buttons for the Rossi/AXRE 4 bolt heeads, Rossi 7.5 and the K&B 3.5, that all work great.
~James

Ok, a little reading material for you James while you get better. I used a RG head "button",, my man with the CNC equip

makes aftermarket air-heads for car/buggy application. When he has a subject engine that has the head and button as

one, he will copy the button and make the aircooled section seperate as after market parts.

This configuration is just a small pain in the butt cause the RG has a "pocketed" case for the sleeve flange and the XM

flange sit's on top of the case. So everything, (button & .003" head shim) are bolted on top using an RG (buggy) airhead

cut down to just the first two fins at "it's" original diameter.

The aftermarket RG button bubble volume is small,, about .16+cc with angled squish and the diameter of the bubble is

considerably smaller than the stock XM. I used the MC59 plug due to its larger volume where the element resides which

gave it barely .18cc volume.

Other than those changes the XM is stock and brand new,, I used my recently refinished XTR as a test boat along with

65% nitro fuel and a 40X53 prop cut down to 38mm, backcut by me (amazing it worked). The muffler halves and all

but one of the three pressure nipples were sealed and I set-up the lower unit to be greased with a small chain saw

grease pistol.

The lengthy break-in process was followed , engine height adjustments made and the needle was goin' in while checking

the heat. I didn't have a third hand to run the heat gun so I used the "grab the head 3 or 4 times in a row" technique

to sense the heat. When it took off, It was impressive, and very loud,, as loud as any piped engine,, but I was running

the muffler!

In the "needling in" phase I had it rich and switched to a K&B1L to see if the lesser volume would compensate for the

rich setting,,, the engine detonated and took the element out. The MC59 was put back in and stayed together thru

1/2 gallon of fuel,, thats saying something right there.

This set-up did make it easier to get to the XM's sweet spot, But, it still requires the right prop and careful adjustments

to get the Dog off the porch. This engine can easily be run in Mod class,, I know a total stock XM can be set-up to run

in Mod class as well but I think the ""success margin" is much narrower with the "total stock" "running water" set-up.

Sub-conclusion is , this is not the final solution to making the XM user friendly for the masses but it's a step in the right

direction. A new button (without bolt holes) that captures the OD of the sleeve flange (making it easier to secure the head shim) and a new airhead for securing everything will be made and tested. The button "bubble" will be adjusted with a

little more "shoulder" (in it's bubble roof) to make it a little less harsh in the way it runs. It runs now like it has a large

flat squish,, guys that run mod motors will know what I mean here,, they seem like they "vibrate" a bit and run a little

harsh.

I'll Be Back!

JW

 

[jetpack]

OPS used to make a low-nitro/high compression head for their .45 Speed engine and are hard to find. I wouldn't mind seeing one of these reproduced. I don't always run high nitro and don't have one of these in my box.

 

[Jerry Wyss]

OPS used to make a low-nitro/high compression head for their .45 Speed engine and are hard to find. I wouldn't mind seeing one of these reproduced. I don't always run high nitro and don't have one of these in my box.

Both examples would have to be used in making the correct volume and combustion chamber shape, thats the way

the machinist would rather do it with the equipment he has. Plus, the engines that they would be made for

must be of popular models so the sales would justify the machining and stocking.

I'm not selling anything myself, the machinist will be doing that, I just want them available if I (or anybody else)

needs something that will make things right. Also, I'm concentrating on higher nitro motors here first and if the need

demands something for lower nitro, then we'll get into that too.

But again, he requires an original example to get the combustion chamber shape, is what he's after first

and then specific volumes required, depth into the sleeve and plug(s) that will be used will also be an important factor.

JW