Deck height and squish for an '04

[elemetal]

I'm rebuilding the top end on my EC300 and needed to get the cylinder replated. Before sending it out I checked a few things and did some minor port clean-up. One thing that threw me (I have read of a few with this same issue) is the piston at BDC is close to 2mm above the transfers with a .5mm base gasket yet even at this setting .062 solder didn't even touch the head....I'm not a big fan of a huge gasket stack and am a machinst so I plan on making an aluminum base gasket (1.2mm) and using regular gaskets to get the transfers close. This means my squish will be even worse, likely around 2mm or more.

It looks like I can throw the head on a lathe and turn it down to get the squish right (and juggle that with the base gaskets a little) but when looking for info on this I ran across RB Designs' site (thanks Ron!) where he says 'don't machine the head'. I'm not trying to build a horsepower monster, just a clean and smooth 300; making sure the motor is lined up the way it was supposed to ususally helps greatly with this. Any reason cutting down the head for correct squish but leaving the original bowl/cc/profile will be an issue?

As I raise the jug and ports I'm assuming I need to change the static PV setting as well ("z" dimension in KTM world)

What is the stock "z" dim spec (top of cylinder to flapper) anyhow?

Thanks for any input.

[wence]

I haven't got any answers for ya mate but I am in the same boat and currently have three gaskets( 1 thick and two thin), under the barrel. The ports nearly line up but are still a little low.
Bike runs great but I will eventually get the squish done or just sell it and upgrade to a '10' or something.
Cheers Mark

[widebear]

There's alot more than just raising the jug and then compensating for the lost compression at stake when changing port timing. Start losing base gaskets till you get 180 to 200 lbs cylinder pressure. It will be smooth , torque'y and flexable and most of all usable. Trying to get high rpm hp out of something that was'nt designed for it is like barking up a dead dogs ass, futile!

[elemetal]

Thanks for the replies.

I haven't degreed the ports yet, but are you saying Widebear that the factory purposely had the transfers and exhaust partially blocked when they set the port timing?

Typically you want the transfers completely open at BDC (exhaust too) for good flow, especially at low rpms. Then you want to degree the port opening times, those are the most important. I'm assuming the spacing between the port heights (will check) is correct but that the jug just sits low.

I thought a few had been through this and could confirm the factory spacing but it looks like I'll have to go through it and do it myself.

[widebear]

Depends on what you want. My thought is , if you want mx power delivery get a yz or rm. I tried raising the transfers, later port timing after bdc and did'nt like how it narrowed the power band. Others may of had success but for the stuff I ride I need a engine thats more flexable, unlike my buddy here.




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[hannesd]

instead of putting more base gaskets to open the transfers fully,why not work with the piston and file/dremel off the sides of the piston where the ports are?
i'll be doing this to my vespa 200 engine (basically 2 strokes are all the same)

hannes.

[elemetal]

OK widebear, that's the info I was looking for. You have done what I'm intending and it made it too pipey. Usually port mismatch is from manufacture tolerances adding up, by dialing a few things in it comes together better. I'm not looking to make it an MX'er so I'll take a close look at the port opening times then see how they balance against the partial blockage.

Hannesd; that's the other way to get better opening response without shifting the power around like Widebear was mentioning, I typically don't like messing with the piston shape, it can cause hot spots etc on any thinner areas. Have to see how things line up before going that extreme but it's a workable solution.

[hannesd]

Originally Posted by elemetal

OK widebear, that's the info I was looking for. You have done what I'm intending and it made it too pipey. Usually port mismatch is from manufacture tolerances adding up, by dialing a few things in it comes together better. I'm not looking to make it an MX'er so I'll take a close look at the port opening times then see how they balance against the partial blockage.

Hannesd; that's the other way to get better opening response without shifting the power around like Widebear was mentioning, I typically don't like messing with the piston shape, it can cause hot spots etc on any thinner areas. Have to see how things line up before going that extreme but it's a workable solution.

i don't really concider that as extreme.
i understand that thinner areas would get hotter than others but it won't be that thin to make a weak spot.
i will be doing that to my vespa, but leaving my gasser as it is, it runs fine for me.
i'm not even using half the power for what i'm doing (trying to find obstacles like fallen trees, rocks and other stuff to crawl over) but i love the torque :-)

[lankydoug]

Four strokes often have thin areas on edges of valve relief areas. These don't cause a problem unless engine is run lean or detonates and then that area is the first to go. You don't ever get something for nothing.

[hannesd]

so i tried opening the ports some more by working on the piston.(on my 200 vespa engine) :-p
the thing i learnt is that its ok to do that on all inlet ports except the exhaust port.
when i did that, it gave my engine less torque, i guess because it can now only start the compression at a later time in the cycle because the exhaust port closes at a later time, giving it less time,distance (stroke) and volume to compress.
it doesn't rev bad at all compaired to stock.

i think i a while i'll put a new piston in and leave the piston,at exhaust port side,alone.
i'll up the compression and play with ignition timing to see how that works out too...

maybe this seems irrelevant to some of you because it's not a gasser, but it's allso a 2-stroker

just tought i'd share this with you.

ciao, hannes.