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]

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)
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.

 

[elemetal]

Thanks for feeding some info back in, hannesd. I get my cylinder back in the next day or so and will take another look at shaping the piston a little. Depends on where the top is at BDC with respect to the ports after I set the squish near where it's supposed to be. Transfers are the ones I might play with, definitely not the exhaust or exhaust boosters; that's like raising the jug for more rev out (not what I want to do).

Might just leave it as is and run it for a while to see what it's like. Have the bike stripped to the bare frame right now but am getting ready for re-assembly. Rebuilt the swingarm and linkage, forks, carb; pressed in brass threaded inserts to eliminate those wood screws in the gas tank (who came up with THAT?!) and did a little pipe, radiator and subframe straightening as well....Hope it behaves like I want it to....

 

[hannesd]

so how did it turn out with the cilinder and piston, did you open up the transfers by working on the piston?

and would you have some pics of those brass inserts you put in the gass tank?

ciao, hannes

 

[iancp5]

I'm quite interested in this shaping the piston business. Not because I plan on doing it but if it works I wonder why manufacturers don't do it? Is it different from raising transfers slightly?

 

[elemetal]

The inserts are 4mm x .7, knurled on the outside with a slit on the bottom, that way (after you press them in) the screw pushes them out into the plastic for more wedging grip. So far they've worked great (none spun when I put the screws in); I also used solvent resistant silicon when installing to help seal the tank and hold them in. Haven't posted any photos here yet, guess I need to figure that out....

I machined .035" off the head to get the squish somewhere near where it's supposed to be; with no base gasket I was getting .088" squish. I used a .3mm base and combined with .035" off the head surface I got it down to around .060" (have to do another solder test to confirm). When I first kicked it over I thought 'uh-oh, too much compression', it was a real mule. When I put a comp gauge on it it blew 190 psi at sea level so its close, have to ride some to see what it needs next. I didn't play with the ports or cut the piston, felt like it was too much, too soon and I needed a baseline of sorts to decide what this motor was like. It will likely be a low end machine (it has the older Gnarly too) but I like rev-out too (my 550 has low end so that's covered) so I may send the head to RB after some riding and pondering.


I got WAY deeper into this bike than I was planning but as usual, if you completely go through a used bike it comes together better than if you do patch repair. Carb had some dirt in it (probaly why the bore needer a re-plate), boot didn't fit right but some soft heat from a heat gun helped it back into shape. Subframe being a little tweeked didn't help so after getting it back everything fits up better. I staightened the rads (rt was a little bent up) and that has helped the platics sit right and fit the mount holes, pipe was the same but after some work on that it's back where it was supposed to be. Had to do a little weld/re-machine on the exhaust spigot, bent pipe had worn it to a weird angle. Wires have been gone through and routed correctly, rebuilt the slave cylinder at the clutch and doing the swingarm/rocker bushes and bearings was a good thing. Have to get new springs for the front, maybe the rear. I had another Ohlins spring here form another bike, it's a 6.0 (I'm 230 with gear) so it's close but I haven't run the sag yet. Put in some spare .48 springs from a WP 43 but I'm guessing I'll need .46's (that's what I run in my 550). New reeds and some basline jetting (#7 slide, 42 pj 180 main with a dck needle), rear rotor was bent so I replaced it with a KTM one (direct swap), pegs were hashed but KTM stockers fit right in....

Two last things I need are a throttle cable (this one is frayed at the top, no good) and a rear sprocket/chain and it's time to see what I actually made this thing into. Still have to get it through DMV but that won't be an issue, can't get a plate though....

Best part is this.....I go out to start it for the VERY first time. I've built a number of motors and usually when they've been completely cleaned up they take some time to fire, gotta' get gas in there, get the start technique down etc. I pull in the choke, give a couple of through strokes to pime it and give it a real kick: Bam the thing lights on that kick and idles (a little high but that's how I found the bad throttle cable)!!! I just love it when a plan comes together....Only done one heat cycle but plan on getting ready to ride it next week (after the cable and sprocket come in)

Things I found and will make a correct list of eventually: KTM rear rotors fit fine and they haven't changed those since '91; KTM stock pegs fit fine but are slightly wider (have to sand down the stop a little to get them to sit flat); clutch fibers are the same as a KTM 550 which are the same as a KX500 (Tusk sells a complete clutch pack for the KX500 for $50 or so).

Have to get barkbusters, skid plate and play with some little stuff to dial the bike in to my preferences but it seems like a solid bike, can't wait to see how it rides.

 

[Skidad]

clutch fibers are the same as a KTM 550 which are the same as a KX500

Very interesting. Don't think I've seen that info posted before.

Do you spend much time over in the Oldies section on KTM Talk? Great stuff over there if your into the vintage bikes like your 550. Some crazy and really cool builds on some of those older big bore KTM's.

 

[elemetal]

Do you spend much time over in the Oldies section on KTM Talk? Great stuff over there if your into the vintage bikes like your 550. Some crazy and really cool builds on some of those older big bore KTM's.

Yeah, I was posting in the '550's only thread' for a year before they even started that section....same sceen name. I'm the one that developed that hydro slave clutch that you machine into the case....I've done at least 10 of those and gave Motowrench and KTM495 the specs to do it themselves. You getting a Gasser was a good indication in my book (I recognized you), I'm following.

I know the kx500 and 550 fibres are the same tab/diameter but the KX ones are thicker (1.2mm vs 2.4mm?) so you have to loose one. No-one has had any slip issues with the Kawi ones and those motors will let you know for sure. I was able to hold one of the 550 ones tight up to the Gasser ones and they were identical; given I didn't get out my calipers but I didn't see a need either.

 

[Dude]

Bringing this back up. Here is the piston from the 240 wild. After running this engine and pushing it to its max and also running it threw several port timing and other 2 stroke software i have confirmed one thing. It sucks lol. The blowdown suffers greatly. gasgas did this for who knows what reason but it was the wrong call. I suspect they did this to fool visual inspection.

Vitos does this on there blaster pistons as well. Its a sure fire way to turn your piston into a paper weight. Does it work not really. In theory sure but when you actually degree it and understand how its working you will understand its giving up more than its gaining.

 

[elemetal]

Cool to see you tried it, sorry it was a piston waste. When you look at it you can't help but think what those cuts are doing to the squish and the controlled burn. I'd think you'd want to keep the cuts steep and small so they have less squish and compression effect but you'd likely get more results with a toroid bowl shape in the head.

I've still only taken my 3oo out for heat cycles but it sure does want to go, can't wait to see what it's like in the real dirt world, it still might have too much bottom end grunt causing it to spin too easy in really loose stuff....I'm going to have fun trying it though....

 

[Dude]

That is a factory gasser piston.