Buckets & Motards 26 August Brooklyn

[Slingshot]

ewww what a crappy shape head..

maybe look for a TF100 head. thay have a waay better profile than that.

and even maybe bore it out a bit..

how far do you wanna go with this thing??

What makes it a crappy shaped head?

I'm thinking a boring it out might be a good option, would just need to figure out what size it could go to.

I'm keen to go as far as I can but budget will be a deciding factor, I am lucky though, my old man is an engineer so can do the boring stuff etc.

Head looks OK to a rough bugger like me. (Could do with a squish tho). How's the barrel? Piston should be cheap - try http://www.motoequip.co.nz and support a KBer - as Sketchy has pointed out.

edit: site seems to be down at the mo...

Barrel looks ok to me, doesn't seem to be any groves or anything.

What's a squish?

Motoequip have one on trademe here but I'm not sure if the barrel is standard or over bored all ready.

[Skunk]

Barrel looks ok to me, doesn't seem to be any groves or anything.

What's a squish?

Motoequip have one on trademe here but I'm not sure if the barrel is standard or over bored all ready.

Pop round and I'll lend you a book - Two Stoke Performance Tuning.

Squish is a 'ring' around the edge of the... fug-it to hard to show with words. It improves the combustion.

I have verniers to measure what you have. Tonys site has the std sizes listed.

[Slingshot]

Pop round and I'll lend you a book - Two Stoke Performance Tuning.

Squish is a 'ring' around the edge of the... fug-it to hard to show with words. It improves the combustion.

I have verniers to measure what you have. Tonys site has the std sizes listed.

Sweet, will probably pop over tomorrow night, will text first.

Just googled squish and found this:

The size of the squish band gap and the shape of the combustion chamber is what varies in achieving that goal. The squish is a part of the head face on the outside of the combustion chamber and is the same shape as the piston top.
The reason for the squish is to force the fuel mixture towards the spark plug as the two faces come together, and the combustion chamber shape is designed to create turbulence to thoroughly mix the fuel and any remaining gasses before detonation.

[Skunk]

The size of the squish band gap and the shape of the combustion chamber is what varies in achieving that goal. The squish is a part of the head face on the outside of the combustion chamber and is the same shape as the piston top.
The reason for the squish is to force the fuel mixture towards the spark plug as the two faces come together, and the combustion chamber shape is designed to create turbulence to thoroughly mix the fuel and any remaining gasses before detonation.

Yep. That's what I was trying to say...

[ajturbo]

check the numbers on the piston..
if tony doesn't have one i have a contact in England that WILL have one... CHEEP!

[ajturbo]

Here's the damage:

but what about the valves?

[limbimtimwim]

but what about the valves?

Yeah, looks like the whole head has melted, melding the valves and the head proper together into a nice sorta domed shape. Weird.

[Rashika]

great stuff guys, brings a big grin to my face to look at the piccies and video!
gimme more!
Sorry to hear about ya meltdown slingshot, but it'll be back and better than ever

[F5 Dave]

OK dude that is chronic detonation that has killed the piston. Detonation is the exploding of end gasses whereas normally the gas burns and heats up pushing the piston down re Boyles law (common myth that it explodes).

Ignition too advanced &/or jetting too lean. I'd bet ignition timing. Stator plate needs to be rotated in direction of flywheel. (anticlockwise). Std position mark is a good start, but as compression increases & an effective exp chamber is put on you may need to retard the ignition from this point.

The head is a non squish type, can work ok on small engines, but not ideal. erm little prone to detonation, but don't throw baby out with bathwater, there is another reason.

As far as CC you can only bore it out to like 104 else you have to keep a 24mm carb. If you want to run bigger you can go up to 125cc but the small carb will be a restriction you can't work around.

[Sully60]

OK dude that is chronic detonation that has killed the piston. Detonation is the exploding of end gasses whereas normally the gas burns and heats up pushing the piston down re Boyles law (common myth that it explodes).

Quite sure about that Dave? Wouldn't there be some vapourised piston material on the sparkplug and the front (exhaust side) of the piston would look erroded not exploded.
Not to say your theory is wrong but all the detonating engines I've seen start to melt at some point, this doesn't seem to have happened here.

I don't know for sure , just my 2 cents.

[Sketchy_Racer]

Looking closely at the pics, I can't say I can see any of the common symtoms of detonation (well.. all i've seen is RS125 stuff. so yeh)

To me it looks almost like the piston ring has caught on the ports. But yeah i would never trust my judgement.

Hard to tell without having a look in person

[Slingshot]

OK dude that is chronic detonation that has killed the piston.

Here I was thinking that it was the burnout that I did just prior to heading out on the track

The piston does look more like it's broken apart rather than being vaporised, when we first pulled the plug out (at the track) the gap was completly closed...I'm guessing that a chuck of piston has been squashed between the top of the piston and the plug.

[F5 Dave]

Detonation can be quite violent or quite subtle - the subtle type burns a hole typically in the middle of the piston or to the exhaust side eroding it away by the port. Or it can violently punch a hole in the top or break ring lands. This is what I suspect here.

. . . Although looking closer at the pics again it is interesting that the ring seems broken at the point & there is more than one broken area.

Hmmm. Is the ring peg at the back still present? Or has it been pushed in? When a ring gets caught it usually digs a trough above the port it gets caught in. Depends how brittle the ring is I guess, if they snapped straight away it would be better but modern rings aren't that brittle usually. What do the ports look like? I always reaaaly chamfer mine. If they were sharp it would be a bad thing.

Yes I saw that burn out.

[Skunk]

It was running pump 98 and the engine was "ported"; so maybe it should have been running avgas?

[Sketchy_Racer]

I'd like to think if that damage was caused by det that bad, even leaded fuel wouldn't have saved its arse.

even if it is ported, i doesn't appear that much has been changed in the terms of compression. that just looks like the stock head to me..