KR-1S.co.uk Forum

I was trying to recover a pitted cylinder head, but to get to 10cc volume, I had to cut a lot out off the dome, to the point that I knew I would never trust the head because I had no idea off the thickness of the material left (and then I was only at 9cc )

So I could have the head rewelded, or opt for trying to make head-inserts for an original head. The second option hasn't been tried, so the descision was quickly made

going through the chamber :



thickness off the head at 56mm diameter ( with 2mm removed from the head-surface compared to an original) :



and ready for inserts :



took some measurements while milling away material, to have an idea of the available material for normal head-machining :



numbers are recalculated to an original head (check the height of the surface on the head-bolts) these aren't exact figures, as I couldn't take the head of the mill for accurate measurements, but might be of help to anyone machining heads ? (might explain the dip at 51 and 47, as it looks rather strange compaired with the other numbers)

next making the inserts, shouldn't be too dificult on a lath. I had to to the head-work on a mill, 'cause the head can't go round on my lath. Due to having to switch tools/centre points not an easy job on a mill to get both ecxactly the same

biggest problem will be sealing the coolant arround the KIPS-holes. There is just enough room to have an O-ring seal go round the entire cylinder, but there is no room arround the KIPS for an extra ring next to the O-ring to seal the combustion chamber

It's a pity someone doesn't make billet heads with interchangeable domes like the LC stuff you can get.
I'm having one of these

http://www.yamaha-rd.com/forum/viewtopi ... 8&start=10

Nice 1 Jan. How are you getting on with the inserts? I think they are the way to go for the 2 stroke. They give you an easy way of replacing and modifying a cylinder head quickly. I especially like the toroidal shapes they are making nowadays. They just look right ,if you know what I mean. My experience from inserts comes from the only area of 2 strokes that in my mind is still advancing to any degree, and that is scooters. Most of the heads for water cooled big bore kits have inserts fitted within O'ringed heads and they are producing some serious HP for their size. Check them out, could give you some inspiration . Keep us posted as I am definitely interested in how you get on

Oops . Double post

ok, I'm about to make the inserts.

finished my calculations/drawings.

some data :

cylindres : timing is a bit raised because of the lower piston's (28.50mm comp. height):
KIPS timing : 196.4°
main exh timing : 190.4°
transfer : 136.2°

head :
RPM max 10.750
squish 0.7mm
squish width : 7mm
volume : 10cc
comp. ratio : 13.5
MVS should be +/- 23 m/s

I want the engine to be safe to run on 98. not a track bike, just a fun toy. And I like kick's in the but, no fan of flat torgue-curves.

Are my figures ok (in the sence that they are all matching each other) ?

opinions welcome, certainly if you are from Australia and have an institute, or englishmen that have been to Bonneville

Hi Jan,
How are things progressing with your inserts?
Do you have any photos yet?
Cheers,
Bernie

not much to see yet, just done the outside diameter so it's a tight fit in the head.

here you can see the insert in 3D -if you have google sketch-up that is. It's free by te way, and was the first time I actually ussed it to design something.

IT'S GREAT ! for lot's of reasons

* you simple draw the cross-section, and than within a couple of clicks, you turn it into a 3D-model !
* it's very easy to use : you simply start drawing a rectangle, type in the measurements and the rectangle is exactly created as
* it's also very good to find out measurements you otherwise have to calculate. for example : if you want to know the radius of the top of a piton, you simply draw a rectangle as the piston, than you draw an arc on top of it that's say 3.5mm high (KR1 piston, you can measure that on your piston), and than the program gives you the radius. for example : MJ said the radius is 120mm, while it actually only is 113.75mm.

here is the link to my head-design: http://users.telenet.be/jannemie/YZ89%203D.skp

first one is ready





anybody know if it's a good idea to make some sort of grooves at the back to increase the surface for better cooling ? or will it disturb the waterflow too much ?

nice work!

Fantastic job =D> =D> =D>
Can't wait to see how well it runs =D>

Nice work Jan, I'll give you 9/10 (but not 18/20)
Your MSV is a bit low but the squish band looks wide enough, the cylinder can do with some help regarding blowdown time. The insert needs a bigger radius into the island around the plug. Should work a treat.
A rule I have if Aprilia have it on their GP bikes then it's needed if they don't have it then you don't need it. Aprilia's have nothing on the back of their inserts.
Nice to see you did the top of your cylinder too.

TwoStroke Institute wrote:Nice work Jan, I'll give you 9/10 (but not 18/20)
Your MSV is a bit low but the squish band looks wide enough, the cylinder can do with some help regarding blowdown time. The insert needs a bigger radius into the island around the plug. Should work a treat.
A rule I have if Aprilia have it on their GP bikes then it's needed if they don't have it then you don't need it. Aprilia's have nothing on the back of their inserts.
Nice to see you did the top of your cylinder too.

9/10 I'd been happy with 5/10 for a first time

So what's wrong with the blowdown ? too smal or to big ?
And what do you mean with the bigger radius into the island ? I've designed it so, that there is always about 7.5 to 8.5mm off material arround the combustion chamber (and a bit more arround the spark plug, a bit like the TSS inserts), with the simplest shape possible on the cooling side.

here is crosssection of it :

I'm talking about the business side(hot) of the insert.
As Jan Thiel says "you can never have enough blowdown time"

TwoStroke Institute wrote:I'm talking about the business side(hot) of the insert.
As Jan Thiel says "you can never have enough blowdown time"

So what sort of blowdown time do you think you could get away with on a KR without narrowing the powerband drastically?