ESE's works engine tuner

**Muhr** · 17th June 2018, 10:49

The block begins to take shape!

**Muhr** · 17th June 2018, 10:53

Originally Posted by wobbly

Well here finally is the result of the change to the semi flat top IAME piston with a 1mm edge radius.

Great stuff! how much duration did you run?

**wobbly** · 17th June 2018, 12:31

The spec for a TM KZ10C selected factory cylinder is 27mm ATDC = 82.54* = 194.92* Duration.
That certainly doesn't mean they actually are.
But with the piston radius , there is some conjecture as to what the real timing is effectively.
It would appear that changing the cylinder height 1/2 the radius on the piston has the effect of great front side power at the expense of overev.
So now I need to experiment with a slightly higher adjustment, then try an increased radius as well.
Does anyone know what VHM did with their option piston and insert using a radius.
They reported a 1 Hp increase , but didnt seem to loose overev in the dyno sheet i have seen.

**TZ350** · 17th June 2018, 16:26

Originally Posted by Muhr

The block begins to take shape!

Looking good. ....

**peewee** · 17th June 2018, 16:35

what could be the reason for not casting in a large bullnose at the transfer inner wall bore face ? https://m.facebook.com/pg/brcracingc...ernal&mt_nav=1

**marsheng** · 17th June 2018, 16:37

I'm rebuilding a T250. I wanted to fill in a bit of the head to make a squish band. Welded a bit, but was full of pores. Dug out 2.5 mm of material to a clean base and tried again. Black soot and bubbles still kept coming up. Kept the heat on hoping that the air pockets would eventually float to the surface. It never happened. Just when I thought it was good the weld puddle rose and a new bubble popped out.

I let it cool and to my surprise, most of the fins had newly formed bubbles on them. Looks like there is something that vaporizes at a lower temp than the alu melt and the creates the bubbles.

**peewee** · 17th June 2018, 17:29

marsh im not sure if this is your first go at something thats been oil soaked for 20yrs but it can be a bit tricky. try adjusting the machine balance so theres a bit more cleaning action. also be sure you havent dipped the tungsten in the weld or it becomes contaminated and puts contamination back into the weld. also make sure you have proper shielding gas flow and no atmosphere wind is disturbing the shielding gas. these are some of the reasons you see the black shit. once you see black its best to stop and grind it out, determine whats causing it then proceed on. other wise youll likely have a million pinholes and garbage when you go to machine it

im not sure of the bubbles. maybe someone has coated the fins with spray paint ? watch out for toxic fumes as well. you never know what chemicals a old head may have soaked up over the years. only use acetone as a cleaner since some brakecleaners can produce phosgene during the weldig process

**ken seeber** · 17th June 2018, 17:57

Originally Posted by marsheng

I'm rebuilding a T250. I wanted to fill in a bit of the head to make a squish band. Welded a bit, but was full of pores. Dug out 2.5 mm of material to a clean base and tried again. Black soot and bubbles still kept coming up. Kept the heat on hoping that the air pockets would eventually float to the surface. It never happened. Just when I thought it was good the weld puddle rose and a new bubble popped out.

Actually I reckon that the head is high pressure die cast, something that the Japs got into with heads, cheaper than sand casting. To assist production, they added zinc and other crap which makes it near impossible to weld. This is evident also in Yamaha KT100S kart engines, making the earlier sand cast heads desirable.
So, what some dudes over here do in these situations is to not try to weld, but to build up by brazing using oxy or even propane due to the much lower temps of the brazing rod. Even though the melt temps are lower, the stuff stays on during running.

Here's just one of many:

https://www.aluminumrepair.com/aluminum-brazing/

I'm sure that there will be something similar of the shelf in Kiwiland.

**Grumph** · 17th June 2018, 19:31

Ken's right as usual.
What I would also suggest is to go see a powdercoater and get anything you want to weld soaked in a Trichlorethylene bath.

**Haufen** · 17th June 2018, 19:58

Originally Posted by wobbly

Well here finally is the result of the change to the semi flat top IAME piston with a 1mm edge radius.
The piston is 0.5mm higher, so equivalent to dropping the cylinder 1/2 the radius.
I can see why the MX guys like this mod - added power all the way up the front side ( +1.3 max in this case ) but it drops off past 14,000.
This I believe is simply due to the cylinder being a little low, so I will next jack it up 0.2mm, and drop the insert the same amount down the bore.
But really what needs to happen next is to not move the cylinder, but go with a 1.5mm radius - then depending upon the result even bigger as Frits has alluded to.

Thanks, looking good. What would be the normal curve that can be expected from a standard setup which is dropped .5mm? I assume that this mod will always be at least a little bit more likely to lack overrev or for the curve to fall on it's face as it works in the other direction, too, thus supports burnt gases to enter the transfers.

**F5 Dave** · 17th June 2018, 21:29

Originally Posted by Grumph

Ken's right as usual.
What I would also suggest is to go see a powdercoater and get anything you want to weld soaked in a Trichlorethylene bath.

Yeah but hurry. You'll need to get there before the turn of last century.

**guyhockley** · 17th June 2018, 21:52

Originally Posted by Mike Fisher

Not a 2 stroke question but... That looks like a Hurst Airheart master cylinder in the inset photo. Did the Enfiled run a rear disc, or was it a rear hydraulic drum brake, in '65?

I cropped the Enfield bits from an article about TT technical trends or some such, think the disc brake was on a sidecar outfit. Not at home for a few days, I'll have a look when I get back.

**JanBros** · 17th June 2018, 22:26

Originally Posted by marsheng

I'm rebuilding a T250. I wanted to fill in a bit of the head to make a squish band. Welded a bit, but was full of pores. Dug out 2.5 mm of material to a clean base and tried again. Black soot and bubbles still kept coming up. Kept the heat on hoping that the air pockets would eventually float to the surface. It never happened. Just when I thought it was good the weld puddle rose and a new bubble popped out.

I let it cool and to my surprise, most of the fins had newly formed bubbles on them. Looks like there is something that vaporizes at a lower temp than the alu melt and the creates the bubbles.

Had the same problem trying to weld a Honda Sky head. nothing you can do about it. After trying lot's of stuff, you think you've got it, but then when you machine the head it still looks like Swiss cheese inside.
I ended up turning an insert and pressed it in the head, and welded the circumferrence for better heat-disipation.

**marsheng** · 17th June 2018, 22:38

Originally Posted by Grumph

Ken's right as usual.
What I would also suggest is to go see a powdercoater and get anything you want to weld soaked in a Trichlorethylene bath.

I milled out 2.5 mm before welding and I cut it dry.

Done enough welding on castings to know this is not normal. The bubbles in the fins are evidence of that. These is something they put into the cast to make it nice and clean on the outside but crap on the inside. That is probably why of the 6 or so heads I have here, 3 are cracked right through the castings.

The brazing looks like an emergency repair method and I'll get some rods. Could be very useful. For long term, either find out how to weld these or cast new ones. I need a long term solution.

These them ?

https://www.aliexpress.com/item/4pcs...813597481.html

Bit cheaper than the local agents !!!

Not sure if I saw it on this forum or not, but a courier said he had 100K on a T250 before a crank rebuild.. So excellent motors.