Bucket development: A few questions for the wise ones

[jasonu]

[QUOTE=F5 Dave;1129774988]

Shit you make me laugh mate. Pity you are too far away for more drinking sessions.

Come on ofer for a visit. I'll buy the beer!!!

[SS90]

something like these:

http://www.rscycles.com/images/vhm_p.../vhm_heads.htm

yes, wouldn't that be nice; but I don't really have access to the required tools to make something like this.

This may sound a little odd, but, if you don't have access to a good lathe set up, believe it or not, you can actually use a Dremel and simply cut your combustion chamber by hand, you just need to make up a template out of flat stiff plastic or aluminium plate, and slowly cut the head out matching it to the template.
It does sound bit rough, but I assure you it does work if you are handy with a Dremel.

Because basic head designs on small engines that produce a good spread of power usually have a squish area somewhere like 60%, it is not too tricky to achieve a satisfactory result, by no way am I saying it is better than using a lathe, but in a pinch, it does work, and plenty of tuners I know have, for various reasons, had to resort to such methods.

[jasonu]

This may sound a little odd, but, if you don't have access to a good lathe set up, believe it or not, you can actually use a Dremel and simply cut your combustion chamber by hand, you just need to make up a template out of flat stiff plastic or aluminium plate, and slowly cut the head out matching it to the template.
It does sound bit rough, but I assure you it does work if you are handy with a Dremel.

Because basic head designs on small engines that produce a good spread of power usually have a squish area somewhere like 60%, it is not too tricky to achieve a satisfactory result, by no way am I saying it is better than using a lathe, but in a pinch, it does work, and plenty of tuners I know have, for various reasons, had to resort to such methods.

Can you say 'COCONUT'?

[SS90]

Can you say 'COCONUT'?

Yea, sure, it's not ideal, but the first head I made for the development cylinder was made by hand, using only a template, and a Dremel (I now have a jig of course). Essentially, all theoretical gains aside, if you have your volume correct, and you squish area is essentially even (all really easy to check), you are going to be be pretty safe.

The first incarnation made over 21 PS, and it still runs today, using a head with a combustion chamber that was made with a Dremel.

I got the idea for the template concept from when I was an apprentice for a Harley dealer way back....you could purchase them as a template to modify your 883 cylinder head to suit a 1200cc conversion using only a dremel.....it worked ok, so I simply adapted the idea for 2 strokes (at the time I had no jig for holding the heads to machine them, and I needed a solution)

In my opinion and experience, if you don't have a lathe, you can make a useable cylinder head for an aircooled two stroke using only a Dremel, a flat piece of Perspex, a graduated syringe (both for ccing the head) and a flat piece of stiff plastic or cardboard (cut to the profile you want to run on your head)

Obviously it is really simple to design and cut out the template from a piece of card or plastic, the only difficult part is to get the finished job as even as possible.

From memory, the finished article has a variation of something like .2mm (so the squish is between 1mm and 1.2mm depending on where you measure it, which luckily enough is larger on the exhaust side, which perhaps could be argued as beneficial, depending on who you talk to).

The power is the same with that original head, or the "series" one we used.

With a central spark plug, and higher compression etc, perhaps it may be measurable, but perhaps not.

"high end" stuff? with out a doubt.

[Buckets4Me]

dont think we have ever used a dremmel to do a head but the idear is sound


just some of the fun we have had

[bucketracer]

.

Where did you find those Pics of Thomas CCing a head? I remember he used brake fluid to make the measurements and a light smear of grease to seal the plastic lid of a take-away container to the head. Anti Freeze would work too, didn't rust anything if it got into the motor, engine oil is to viscous to make good measurements, and would trap air bubbles.

Chambers works out his exact corrected CR by setting the piston just at exhaust closing, CCing the cylinder above the exhaust port, then CCing the clearance volume in the head with the piston at TDC.

[F5 Dave]

your local engineer or engine reconditioner will have a lathe & a few educated guesses will get it sorted fine. If yo own a house & don't intend moving a lathe can be bought for $500. You won't look back.

[speedpro]

I used to have a cheapy 4-5' lathe and it had no end of uses. i too have carved out combustion chambers using a dremel type tool. My McIntosh head is radically altered and I've done a 2-stroke with success as well. If you have plenty of time and patience you can do all sorts. I've even filed back a welded up #2 main crank bearing support on the Z1. Took ages but the end result was perfect.

[Bert]

..........If yo own a house & don't intend moving a lathe can be bought for $500. You won't look back.

its a good point Dave; but i haven't had that much joy finding one local (ish) for ~500 most seem to be too big or to expensive.

[Yow Ling]

if you have 3 phase they are even cheaper, bit too much competition for the single phase ones

[F5 Dave]

Yeah that's true, I was lucky with the 3 phase.

[Bert]

not hard to do a motor conversion though, but you still have to find one.....

[Bert]

another Question

back to primary compression ratio, what is the best way of measuring this? (outside of sitting the motor flat and poring in fluid; measured); is there are trick to this?

does one have to measure the transfer& boost port volumes as part of this ?

I start to re-reading Jennings (but I'm a bit slow on the up take)..

[speedpro]

Going by the number of people I know who have ever measured it and who have a reasonably fast motor I don't think it's worth measuring. Any changes you could make are only going to be marginal, limited by the typical bore and stroke and the typical crankcase configuration.

[SS90]

I have to disagree on that Speedpro.

The opposite is true for my experience. If you are developing one engine only, it is a good idea to find out what you are starting with, because sometimes you find that an engine that is designed for road use, has gains to be made, be they increasing or decreasing the volume.