I think I broked it

[Sully60]

Friends don't reccommend 4-strokes to friends.

They do if they race each other

6.2kW Phwoah!

[quallman1234]

That's why I buy circlips in packets of 10. If I pull a circlip out of a piston I always twist it up and wreck it so I cannot be tempted to try and use it again. They're cheap. Sounds like you need to be checking dimensions pretty carefully on the next piston and also looking at squish clearance etc. If your new piston had a skirt that was lower than the original piston then typically that piston will also have a lower deck height. Your compression may have been 5:1 with a 3mm squish clearance. Not exactly a big horsepower setup. (edit) just re-read thread and you did measure. Funny then that it should interfere with crankshaft.

Cheers for the advice, methink's im going to go out and order a pack of 10 circlips. Just to do this for next time!. Most of my bike's run 14mm guagoen's so thats convient.

The orignal piston was also very close to the crank? I was wee bit worried that when hot the piston would sieze on the crank but luckily it never had the chance.
I have a spare piston and barrel, only problem is one of the exhaust threads has been fucked and then attempt to be re-thread (insert ivan abuse here).
Going to have to put a helicoil in it, or i could weld it up redrill it and tap it.

The bike is an awesome handlier it would be a true beast, im considering poping a 150 Loncin in it, infulenced by Kendog's new beast!. Ive noticed on loncin's website that they have a look of high capciator but low power output engines. 6.2kw ain't going to cut it!
But i might stay with the AX engine for a little while, im kinda getting into this tuning buniess a little bit. Gotta read some books!

[speedpro]

You're onto it. Do a bit of reading, buy some measuring gear like calipers and syringes and get into it. The only way to build a fast AND reliable motor is to do everything real carefully and exactly as per the book. Keep in mind the limitations of the rest of the engine when designing. For instance the AX only has a 4-speed box I think so it will be no use tuning for 22hp over 1000rpm cause it just won't work, unless your name is Dave Trustrum and the AX clutch is better than I imagine. Pick Skunks(and others) brains as well but be careful if advice is contradicting the books. Unless they own a particularly fast bike go with what the book says.

Tyres and brakes will get you round our small tracks fast as well if the motor is acceptable. You hardly ever use heaps of power but it is fun.

[Skunk]

My advice - use the AX engine for learning the tuning skills. As an engine they're good, as a gearbox they're crap.

The clutch will handle a reasonable amount of abuse. Don't know if you listened to me last round - abused it at both ends of the track. Has been abused for a while (3 years) and shows no signs of slipping.

See if you can get a squish machined into the head - std they don't have one. Mines setup to 15:1 compression but the porting was done by an expert (Pete Sales). I don't have any measurements yet other than 189° exhaust timing (89.5° ATDC). Hope that makes sense. Effective Exhaust Port Dia is 33sq mm.

As you know I run a 28mm flat slide and I think it's a little big for the slipway... I could well be wrong. It ran fine with the 18mm (better mid range) so my thoughts are a 26mm might be best. Maybe a 28mm round slide?

Build a chamber that suits YOUR engine and YOUR riding.

[quallman1234]

Cheers, any advice on how to measure, the exhaust port angle's

Make a mark on the flywheel or something similiar to that?.

First thing's first i think the best thing is if i measure a bunch of stuff and see what i have and go from there.
I do have a tf100 head with a squish in it, what fits on top of the ax100 engine nice enough, but i don't think it such a good idea.

Im going to have to go to 1mm OS, me wonder's if it will interfere with the crank at that size.

[Skunk]

Bore doesn't affect stroke.

[koba]

Another thing about sticking with the AX engine is you could buy the cheap chinese copy if you totally blow it to pieces.
Looking at the way your bike handles, even with sub-standard tyres I would say you don't even need that much power for the slipway at least.

I wouldn't mind having a go at machining squish into a head if you have a spare one that is ok If I fuck up. \
Depending on how difficult it acutually looks with the AX head and if I think I cando it and all.
I noticed looking at Helens a100 that It wouldn't bee too hard for that head.

[quallman1234]

Bore doesn't affect stroke.

I know. But it could be a slightly longer piston for some reason? Just assuming that's why the 0.5OS piston hit the crank? Maybe. Who knows!, Being aftermarket piston's and all its possible.
If it happens again, ill video it and send put it up here.
Koba, let's not jump the gun just yet, I do have a spare head what won't matter if ya fuck it up, what i doubt knowing you.

First thing's first. Im going to measure everything up first, on both barrel's choose which one is going to be easier to edit, get it bore'd out, and go from there. Once that's done and i have worked out the appiroate squish etc, ill let you have a go (and watch so i can learn something about machining).

[koba]

ill let you have a go (and watch so i can learn something about machining).

Cool, so we can both learn as I go!

Good smartbrain doing all the thinky bits first.

[speedpro]

Sequence of events - Get new piston, fit new piston, machine base of barrel or build spacer to get transfer timing right, machine top of barrel or head to get squish right. The trick with machining squish is to get the clearance AND the compression right at the same time. If you are lucky you will be able to machine a nice combustion chamber including squish and then just machine the top of the barrell to get the desired squish clearance and compression.

Once you start getting the compression up over 14:1 it takes very very little machining to take the compression up LOTS higher. Measure 2-3 times for every cut.

[koba]

Sequence of events - Get new piston, fit new piston, machine base of barrel or build spacer to get transfer timing right, machine top of barrel or head to get squish right. The trick with machining squish is to get the clearance AND the compression right at the same time. If you are lucky you will be able to machine a nice combustion chamber including squish and then just machine the top of the barrell to get the desired squish clearance and compression.

Once you start getting the compression up over 14:1 it takes very very little machining to take the compression up LOTS higher. Measure 2-3 times for every cut.

Cheers for the great advice.
General questions:
Does the AX have a plug in the centre of the head, or offset like an A100?
If so should it be moved to the centre in a performance engine?

[Skunk]

Plug is dead centre. I have a head here if you want a look.

[Number One]

I'm pleased you figured out it is broken before you gave me a trip round the Slipway on it -that way I can't be blamed for breaking it now get it going nice and good and I'll let you have a turn on one of our machines as a swap

[speedpro]

Plug to be central or not?? I've built an engine with a head that had the plug offset to one side. I dynoed it and had it runing as good as possible. I then welded up the head and relocated the plug to the centre of the chamber. There was two things here - the plug was relocated and the combustion chamber shape was improved. The compression ratio was exactly the same. I got about a 15% increase in horsepower and the spread was significantly improved. This was a RGV250 cylinder.

[k14]

Can you run a bucket with compression ratio of over 1:14?? I run my 125 with ratio of 1:12.8 with avgas. Any higher and you may get slightly more hp but you loose over rev and it narrows the power band too much.

Whats the most you can run on a 4 stroke??