Farm boy’s Rattle-can Racer

The Jimbonaut said:
Mmmmm, blonde des Cantons - that'll take the edge off anything, even a sheared bolt ;)

Don't know much about these bikes (i.e. anything) but do know it's in good hands and do know I love that fairing. Here's to an Easter win!

I do love the blondes
And the fairing
I bought most of this crap for the squish heads, the fairing sold me on the rest of it.
The guy was a real character, he had stuffed one of these gt500 engines into some 250 ducati frame...


Back on topic here, i haven’t CC’d the heads yet, when doing that do you include the volume of the squish band or only the dome?
Glad to know the ignitions mount up that way originally, i was pretty worried.
I still don’t like the rotor being stuck out there like. Might have to find a way to mount the stator a bit deeper into the cases.
 
Head volume goes out to include squish bands. How did the PO seal the head to barrel joint? Looks like there is a step in the liner, so those surfaces should be lapped together for a good seal.

Seriously, that ignition looks just alike a TZ mounted that way. Nice and neat and tight in to the crankcases. Check that the two small outer magnets align with the steel part of the pickups. And the carbs are 36mm from your other post. They look pretty close from that picture. As long as all the resistance readings are close to stock it should make spark from less than 500 rpm.
 
teazer said:
Head volume goes out to include squish bands. How did the PO seal the head to barrel joint? Looks like there is a step in the liner, so those surfaces should be lapped together for a good seal.

Seriously, that ignition looks just alike a TZ mounted that way. Nice and neat and tight in to the crankcases. Check that the two small outer magnets align with the steel part of the pickups. And the carbs are 36mm from your other post. They look pretty close from that picture. As long as all the resistance readings are close to stock it should make spark from less than 500 rpm.

The heads were sealed sans gasket, there is a step in the heads and barrels. A few twists with some lapping compound is in order. I never use head gaskets if the joint is like a spigot.

Glad to hear the carbs are all 36’s, 38 would have been a tad big i think.
The magnet does run in line with the pickup coils.
Talk about tight clearance, .6mm on the top laminate, 0.65mm on the lower laminate.
Hopefully the rotor doesn’t decide it wants to move around in there.

If all goes well, the heads will be CC’d tonight, and the squish at least measured.
 
So, did not have, nor will i have time for squishing putty tonight.
I did get a chance to squirt some oil into the combustion chambers.

a1264bb20471f11b5d998b7b9f778dc6.jpg


In the image, there’s 12cc in each, but i think they are over full as the piston is domed.
11 is probably the safer amount to use going forward in the calculation.

So there are 11 cc in the combustion volume.
And with a bore of 71mm, we get a radius of 3.55cm
Pi*r*r =39.6 cm^2 with a 6.4cm stroke=253cc
So if i have
1mm of squish = 3.96cc+11=14.96cc
1.2mm of squish= 4.75+11= 15.75cc
1.4mm squish (ewww)= 5.54+11= 16.54cc

So compression ratios
1mm= (14.96+253)/14.96= 17.9!!!!!!!
1.2mm (15.75+253)/15.75= 17!!!!!!
1.4mm (16.54+253)/16.54= 16.3!!!!

And i’ve now decided to run this thing on methanol...
Completely unrelated decision

Should procurement of methanol prove to be a PITA up here in QC, i would probably need a 12.5:1 ratio at the most.

(X+253)/X=12.5
12.5x=x+253
11.5x=253
X=22cc

So i need to add 7cc to the combustion chambers

Which have a radius of 51mm
2.55*2.55*pi= 6.5cm^2
I need to deepen the C.C. By 1.07cm...
Fuck
 
Running VP m3 fuel (turns out a vendor is 15k from my place) will probably require somewhere in the 15.5:1 or 16:1 compression ratio range.
15.7:1 (a. bell p.24) will require adding 2.25cc to the Combustion area. So i need to deepen the center by 3.5mm... still better than 10.

This thing may just have picked up a lot more boom.
 
TZ runs close to 15.5:1 geometric and runs happily on anything above 100 octane. My personal preference in VP range is U4.4 which seems to provide great throttle response.

Back to your calculations. If the head volume to mating surface including squish annulus is 12cc, we can calculate compressed volume. 14mm deep chamber with 51mm diameter (inside squish band) less piston crown volume = 15.6cc. At 12cc, yours must be closer to 25:1. Well that's not right.

Please re-measure to the volume to the surface that the head and barrel meet which is presumably to that machined ring just outside the squish band. Please also confirm diameter of the chamber just inside the squish band and overall depth of the chamber. Piston crown height is probably around 4.6mm from edge to top of the crown - please measure and confirm before you do anything to the chamber.

If I am right about those heads, they were machined by RK Tek - see P5 of http://www.2strokeheads.com/info/platteville_ic_design_paper_2008.pdf to see what they look like after machining. RK Tek heads run higher compression than stock and I am sure he pushed my reprofiled TZ350 head up to 17:1

In fact he has your heads on his web site - or some similar ones.. http://www.2strokeheads.com/VintageMX.htm
 
I had seen those rk heads before, i think my cousin runs a set on his polaris IQR 600.
I had seen them also when i was looking for some for my other titan engine. Those are just stock heads that were welded and machined out.

Back to the CC measures, they way i figured 11cc not including the squish clearance was that i filled the CC with 10ml, and put the piston into the head.
It barely touched the oil with the top.
11cc is the point where putting the piston in would displace the oil to the inner edge of the squish band, without being pushed out into the squish area.
That way, any additional volume can be calculated from the area of the bore and squish clearance.

Definitely not going to touch the heads until after a test run with the m1 fuel.
Not looking to fling several hundred bucks out the window for nothing.

In the event that the ratio proves to be too high, would it be an option to reduce the squish area opposite the exhaust port?
I don’t know how much deeper the CC can be made without it being overly weakened.
So would machining a shallow offset CC be a better way to go here?
 
Popped open the carb bowls today to check the main jets, 310’s so i guess the PO did not run it on alcohol during its few dyno test runs.


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Teazer,
height of piston crown is 4.6mm
Depth of CC from the edge of squish band is 13.7mm
Width of squish is 10mm
Width of CC at edge of squish 50.5mm
Bore
 
Just figured the heads out, he cast and machined them himself.
Used a set of standard heads as a plug to make the mold.
dde75169c68d8e44801f25624f9dfe62.jpg

0ef6794a0c46a891f29a6aec820b3c25.jpg

Notice the subtle differences and where they come from
8cfc47e0a9699a85e11bf88867c1c7b6.jpg


Squish measured in the 1.7mm range for both cylinders
 
I used 51mm 4.65 and 13, so not too far off. I tweaked the data and depending on the exhaust timing, compression seems to be a little high, but try it and see what happens.
 
Question, is it a terrible idea to lower the crown of the piston?
In the interior 51mm i mean?
I measured the thickness of the heads at the top of the chamber, there’s about 12mm of metal there. Not really enough to deepen the chamber at all.

Edit: going to try some of that VP U4.4
Rather stay away from methanol/ethanol fuels for the time being.
 
Great project, following along eagerly.
With regards to the CR, do you have enough parts to assemble the top end and then measure the volume at TDC? If you can you remove all the guesswork with regards to piston dome and position. Once you have done that you have an established basepoint whereby you can then go ahead and measure your combustion chamber as you have done previously then modify it to get the CR/squish that you desire.
 
Pete12 said:
Great project, following along eagerly.
With regards to the CR, do you have enough parts to assemble the top end and then measure the volume at TDC? If you can you remove all the guesswork with regards to piston dome and position. Once you have done that you have an established basepoint whereby you can then go ahead and measure your combustion chamber as you have done previously then modify it to get the CR/squish that you desire.

If you knew how hard i just face palmed myself there...

The worst part is i thought of that and told myself i should do it that way, can’t remember why i didn’t.

Slap a bit of grease around the edge of the piston, put the head on, fill with oil from a syringe...

Man, i feel retarded this morning.
 
Haha, no problem ;D
Don't forget to torque it to specs for gasket crush then fill to the top of the plug hole then subtract that volume and you'll have some workable numbers.
 
There’s no gasket to crush here, except the paper base gasket, but i doubt that it’s going to compress enough to throw the readings off.

Hopefully this yields slightly better numbers and that the previous values were simply due to my incompetence.
 
If you have the pistons, that's the best way to do it.

Stock heads are not very thick, so if the PO cast them the same way but with squish bands, CR will be really high. That said, if you do need to take some meat out of the chamber, do it by changing the radius and not the depth. Make the roof slightly "flatter".

U4.4 is not their highest octane fuel. If you need more knock resistance, yu can go to 110 or even 116 fuels. Sunoco Maximal is also pretty good, but lacks the snap that 4.4 has.
 
Alright, i will keep that in mind teazer.
Will try some C16 first, brother in law runs it so i’ll see if i can grab half a gallon from him for initial testing. I just don’t want the damn thing blowing up on me in the first 5 minutes of its life.


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Got a quote for shits and giggles on a 5 gallon pail of u4.4 and c16.
151$ for U4.4 and 169$ for C16.
Probably going to want to set this up for some premium 94 unleaded if at all possible.
0146ef25537691ccac03b6df4fb3db3e.jpg

Head is on, with a touch of grease around the piston at TDC, holding 20cc of oil, with 2 in the plug hole. 18cc heads, 253 cylinder, works out to 15.1:1
I can live with that but the squish is on the loose side of things here.

Previous owner claims they ran it on pump fuel, so i guess it will all go back together as is for its inaugural test fire.
 
Teazer, dumb question here probably, but if i run this thing with only the top ring that removes the possibility of the lower ring getting stuck in a port. The locating pin for the lower ring directly opposite the exhaust port, and without it opens up a sizeable area to add a boost port.
Was wondering your thoughts on this. Can this motor handle the benefits that are to be gained? Are there any?

e3c9515816f4ea09098fbf99dfd843b7.jpg


I penciled in where the two pins are and where i though the port could be added.
 
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