ESE's works engine tuner

[TZ350]

Did you keep the compression ratio and the squish gap constant during these gasket changes? Changing the squish gap 0,5 mm can have the same effect as changing the ignition timing several degrees.

I did my best to keep the compression ratio and squish the same.

So it didn't seize and the piston crown didn't cave in, but how about the piston ring? I've seen engines that ran hot with no apparent ill effects, only they were a pig to start afterwards: the piston rings had lost much of their tension. Things like that can keep you searching for days.

Thanks for the heads up, the ring certainly did look a bit limp.

[teriks]

Profile, left and right. Wiring time.

Cool, that's a very different layout for a dirt bike!
What will you do with the intake side? Seems like quite a challenge..

[Flettner]

Cool, that's a very different layout for a dirt bike!
What will you do with the intake side? Seems like quite a challenge..

The plan is to cast a new side case with a sealing flange (a bit like old Kawasaki RV engines) so I can cover the whole inlet / throttle drive, with perhaps a chance to try my hand at some carbon fiber to make a nice light cover. The airfilter will be where the radiator once was. Even with this side cover it will still be thinner than a standard YZ if you include the YZ's chamber at that point. This set up will be good enough to run round the yard and dyno with just a pod type air filter hose clipped on. Still a wee bit to do.

[Flettner]

Thank you Frits, I couldn't remember the exact details.
Thought I might be down some 'quantum physics' STIC worm hole.

[TZ350]

So it didn't seize and the piston crown didn't cave in, but how about the piston ring?

In the tradition of Bucket racing.

For the price of a new ring, I got these beauties off a Japanese auction site, seven NX4 piston assemblies. These had been religiously changed at Honda,s (money making) suggested maintenance intervals. These will be great, they are like new and will be good for all sorts of experiments, like radius-ed timing edges. Any one of them will run for ages in my Bucket, or at least until I over heat it again, but then I do have a few spares.

[F5 Dave]

Ooh, do they come with circlips fitted?
Do you realise if you repack an old muffler and its really oily you can squeeze that right back into the oil container?

They smear the ring lands over where the bridge bears. Check there for ring freedom.

[TZ350]

Do you realise if you repack an old muffler and its really oily you can squeeze that right back into the oil container?

Ok "waste not, want not" it is,
I was't going to tell everyone that tip about recycling the oil, it was supposed to be our little secret, but you blabbed ..... ....

Thanks for the reminder about the ring lands, I will check them.

I love Bucket racing. .

[Brett S]

Here's a hot Bucketeering tip, put anti seize on your piston skirt to stop it seizing.

[speedpro]

Do you realise if you repack an old muffler and its really oily you can squeeze that right back into the oil container?

Whatever you do don't use something flammable to pack a muffler. Learned not to do that after covering the floor at dynotech with little pieces of flaming material

[TZ350]

Here's a hot Bucketeering tip, put anti seize on your piston skirt to stop it seizing.

We have plenty of that, but I could do something better:-

Super Finishing and Stealth Coating:- https://www.facebook.com/pg/SuperFin...=page_internal now that is some slippery shit.

The plant is real close to us and did a piston assembly for me the other day. My motor has the rod assembly, bearings, gearbox and rotary valve have all been super finished and stealth coated.

[F5 Dave]

Whatever you do don't use something flammable to pack a muffler. Learned not to do that after covering the floor at dynotech with little pieces of flaming material

Hahaha, Chris had carpet in there too.

[flyincat]

You had me searching for quite some time: "Where on earth did I write 15* aTDC?" But that has been cleared now.
Nevertheless your original question deserves a reaction.
WOT combustion may take somewhere between 43* and 60*. Ignition delay is the time or the number of crankshaft degrees between the occurence of the ignition spark and the first instant when a temperature and a pressure rise because of combustion can be observed.

I took the values of the Aprilia RSA and a more mundane 125 cc engine for comparison.
Power @13000 rpm . . . . . . . . 54 . . . . . . . . . . . .40
ignition timing bTDC . . . . . . . .14* . . . . . . . . . . .18*
ignition delay. . . . . . . . . . . . . .7* . . . . . . . . . . . .9*
combustion duration . . . . . . . 46* . . . . . . . . . . . 60*
combustion completed aTDC . .39* . . . . . . . . . . .51*

While we're on the topic of ignition timing and combustion duration, I have a question about bore size. I've seen Wobbly, and maybe others, state that a fast water cooled 125cc should have ignition timing in the range of 15* BTDC at peak if everything is near optimal. Is this peak torque OR peak power OR both?

Also, how loosely does this apply for much larger bore engines, say 80mm or larger? I assume it comes down to the combustion duration. Can combustion duration be similar in large bore engines to a 125cc? Another scenario would be going from big to bigger...going from 80mm bore to 85mm bore, the old practice would be to throw a few (+3*) timing at it to account for the 'longer burn time' from the larger bore. Does that make sense or is that old practice just masking a problem?

[Frits Overmars]

I've seen Wobbly, and maybe others, state that a fast water cooled 125cc should have ignition timing in the range of 15* BTDC at peak if everything is near optimal. Is this peak torque OR peak power OR both?

Both, more or less. The RSA for example has 16˚ at max.torque (12500 rpm) and 15˚ or 14˚ at max.power (13000 rpm).

how loosely does this apply for much larger bore engines, say 80mm or larger? I assume it comes down to the combustion duration. Can combustion duration be similar in large bore engines to a 125cc? Another scenario would be going from big to bigger...going from 80mm bore to 85mm bore, the old practice would be to throw a few (+3*) timing at it to account for the 'longer burn time' from the larger bore.

Combustion duration, expressed in seconds, will be longer when the bore gets bigger and the flame has to travel over a greater distance.
But as the bore gets bigger, the specific angle.areas become smaller and the revs must become lower in order to maintain the optimum specific time.areas.
Because of these lower revs, the combustion duration, expressed in crank degrees, will be largely independent on the bore. And the same goes for the ignition timing.

In reality, big singles often have a couple of degrees more ignition advance as a consequence of the fact that big singles are usually found in MX, Enduro and similar forms of agricultural racing, where combustion duration is a bit longer because the engines are not as highly tuned as the small-bore units used in road racing and karting.

[jasonu]

The Classical Performance/Development Curve. .



Cheers, Daryl.

How about a money spent vs gains graph...

[Pursang]

big singles are usually found in MX, Enduro and similar forms of agricultural racing, .

AGRICULTURAL RACING!




Cheers, Daryl.