Adjusting squish band without head gasket

[dyrberg123]

Hi Guys,

As i want to play with the squish band on my T350 i am curious to hear if anybody have experience running without head gasket?

Maybe with some red high temp sealant. I know this was done on many Yamaha LC's

Both head and cylinder have been worked on a lathe so i assume the surfaces are 100% straight.

I am running Kawa h1 heads, with 50% squish, and i have just done the solder gab test, and landed on 1,55mm, witch is a bit
too much isn't it? And it was a true pain gettint the to run true in the lathe, there for to get it running i could take out the 0,5mm gasket
and the i would have 1,05 - 1,1mm.

Otherwise i have two alternatives, cut the heads Again, witch i would perfer to do NeXT Winter as the summer is now here, or make a custom copper head gasket out of 0,2mm copper foil...

Please help guys

[Craig380]

Like you say, this used to be done on Yam LCs, but you need to 'lap' the mating faces of the cylinder and head together using grinding paste, and even then you might not get a proper gas-tight seal.

However, 1.5mm squish with the gasket isn't TOO wide and is probably a lot closer than a factory T350 -- why not see how it runs like that first, and then you can always try without the gasket later?

[dyrberg123]

You could be right there... Maybe i should try..

Have any one tried it on a aircooled twin? And what difference will a 1,55 gab be to a 1,1mm?

[tz375]

1.55 is pretty much too much, but OK to start with. Take the heads off and cut a groove to take a TZ350 or 750 O ring and throw away the gasket after you test cranking compression.

[Suzukidave]

On top of the squish clearance you need to think about head chamber volume .

[dyrberg123]

Thanks Guys,

I allready did a compression test, fitted the gauge and kicked her 5-6 times until it didnt go higher, i read 135 - 140 psi on both. So maybe i should stop cutting corners, take the heads of and take off 0,5 mm, and making sure i have the same volume, as the 135 - 140 is pretty close to what i have been suggested. About o-ringing the heads, this operation have been considered many times - but i cant find any data about the depth of that groove.
Should i use factory reccomended head torque, or go a Little higher?

[ja-moo]

I don't know what your heads look like, if there is no "step" in the head before the chamber starts, then the squish clearance will not change.

[Vintageman]

dyr.

I had 150 PSi with OEM T350 heads (you have modified H1 heads correct?).

I raised EX 2 mm (30.5mm) and it went to 145 PSI (new rings too the others gap was half way to limit) .

Not sure how may gauge calibrates versus yours but it is not too old and quality one.

If you torque too much with only 4 bolts at corners it will bow up in the middle. I would use light oil on bolts threads and head to bolt washer and use middle torque value. Oil ensure you get it versus the torque being blocked by static friction


Have you run this bike yet?

I think I went too far Ex timing for my liking. I think if I raise my compression I will get back "staying" power in the 5000 - 6000 rpm range. Funny below and above don't have this observation.
.
Had this same staying mid range issue on another bike when added racy chambers only. Was advice to raise compression... ran half thickness head gasket (1mm to 1/2 m) got better. Later, I had found I had worn rings (another story). Once this was fixed it is very much better and not a complaint at all. So same idea, but different root cause as why not enough compression.

I think your squish gap has a range where it serves its purpose (fuel there does not ignite… smaller distance for flame travel …) then your good for that goal. If you get it tighter and without mechanical interference all you are really doing is improving gas mileage for less % of overall fuel not fully ignited.

But, if overall compression too low not as much power noticeable when engine not running in power band.

Would like to know how yours runs overall when you are ready. I think you went 29.5mm Ex

[dyrberg123]

Hi Guys,

I took the day off, (off from family) and went to Work and did the right thing, 0,4 - 0,45mm off the heads, so now i have the correct squish 1,1mm

Also i took off a Little inside the cumbustion chamber because the 0,4 off would raise compression, so hopefully i will be on 140psi still.

The reason for all this is that i in the first calculations forgot the head gasket in my math. So i had it on 1,1 until i added the head gasket, jerk i am... BUT learning every day..

And i went out in the shop tonight, got it all back togheter, play a Whole lot with the DG to make them fit, had to cut the Whole downpipe of the right one as they apprently aren't twisted excatly the same, but got that alligned, wow that helped! Also got the stingers tac welded on, so only thing missing is the flanges and end Cans. In the Picture below i have just slided the Cans over the stinger to see - but looks great to me

BTW vintageman, what did you end up with in your ignition timing - 2mm ?? I have the ex on 30..

[Vintageman]

dyr,

That looks nice! Those pipse are tucked into frame extremely well and neat. Stingers looks nice. And like the look of the H1 heads.

I actually tried 20 degrees and after a short time 22, then went to 23.5 degrees. each helped that midrange I mentioned. The Kaw S1 is 23 degrees and has a peak at 8000 RPM.

Last time I took it for a long ride and mostly hammered it. That is how it wants to run. funny it has very good in in city manners running 20-35 mph 4-4500 rpm under light loading. I just won't hold a medium load/grade 5000-6000 pm running 25 - 50 mph. With timing as stated if I give it more throttle it wont give any more power... at least it won't die out like when i was "jerk" and timing was way off. >6500 and up it runs fast and holds any grade ihave around me... but always well above speed limit before you know it.

Hmmm I tink I am goingto take it for a ride after this post

When I get a chance I am going to take 1/2 to 3/4 mm of head to get back some compression. I am confident it will help my goal


My other T350 is a much better running engine more what I like.

Now that I think about it I should compare compression even if just relative vs absolute

I wish I knew how my gauge compared to yours.

[Vintageman]

T305 cyl, late T350 heads, 1mm OS piston, 2mm raised ex port, carbs and air box attached and exhaust on
= ~133 psi both sides carb WOT several kicks room temp ~82F

T350 cyl, late T350 heads (not T305), 0.5 OS piston, stock ex port carbs and air box attached and exhaust on
= ~143 psi both sides carb WOT several kicks room temp ~82F

Not sure why this time T305 is ~10 PSI less. It was a much cooler the day i measure higher and I had no carbs nor exhaust attached, and cyls were well oiled up from freshened up top end just put together. after Ex raise

I think the point being the T305 with the raised Ex port is a full 10 PSI less per cyl than the stock T350 cyl.
The 350 has only a 0.5mm larger piston all else same so that is a real diff between them.

I do think a little more compression may help what I am wanting

I did also note the T305 plugs were much darker than t350 (same carbs/jets, plugs, air box, chambers...).

I wonder with a raised Ex if I should actually reduce my jetting. Not sure how that Ex change affects main jetting in general?

OK i hijacked enough. I wait to hear the review of how your Mean Green Rebel runs

[dyrberg123]

I can't wait either to kick her Hoping i will have time tonight to get the Cans fitted...
Strange with the drop in your compression though, thats odd. I think raising compression will have a nice effect on your mid range, as long as you don't go to high and get the detonation.. Acces to high octane fuel will be a friend, here in Denmark we can get 92 + 95 and also Shells Vpower they call it - 99 octane. All unleaded, but the 99 runs great..

Two questions - the 23,5 deg btdc what is that in mm? And what torque are you using for your heads? I have a copy of the original T350 service manual, bought on ebay from Paul Miller, but says nothing about torque spec

[dyrberg123]

BTW mine was running with std heads and porting + chambers before i took it apart. Keihin PWK 28. Ran perfect.

I have also lowered the intake floor 2mm and widend it 1mm to each side, so i don't have the bottleneck effect there anymore.

So i am sort of hoping that the changed timing and port size witch will need more fuel, will go hand in hand with the squish band heads witch normally needs leaner mixture... HOPING...

[Vintageman]

Look under twins - torque here -
http://www.oldjapanesebikes.com/mraxl_G ... specs.html" onclick="window.open(this.href);return false;

I shaved my piston 2mm. did that first and alone was a decent change over stock for what i like. So we are similar on intake.
Have you seen this post? viewtopic.php?f=5&t=8079" onclick="window.open(this.href);return false;
figure 4 Intake only timing changes and fig 8 Ex only changes sure matches my experience so far.

Yes not sure why compression lower. Maybe the things I noted. But, I was concerned and pulled head off it today for look see cyl walls look very nice (sigh of relieve).

The stock later T350 Head has ~ 0.024” step parallel to cyl walls before dome shape of head begins. I plan to drop them off tomorrow at machine shop tomorrow to shave off 0.018/9” leave an 0.005/6” lip

You would think more fuel for aggressive timing…. Not sure now.
Maybe Tz or Jamoo can advise main jetting change when the change Ex port timing if it mattered

How I guestimate timing->
The plug angle is 20 degree.
Suz gives direct measurement (plug hole) what timing BTDC for 20 degrees (2.05mm), 22 degrees (?? Can’t find now… book mark at work ), and 24 (2.88) degrees. I have just been using linear interpolation between these three values to estimate other angles so some error +/- ¼ degree. Last I set my timing I was shooting for 0.100” which would be 2.70 mm indirect per Suz way.

[dyrberg123]

Hi Vin, thanks for the thread, interesting reading....

What do you mean by plug angle is 20 deg?

I will, have to return to my lathe tomorrow, the supplied flanges that came along with the silencers should be a slide fit over
an 1" od tube, but it is 0,1 mm too small - BUGGER. And since the stingers already are welded on i have to do it to the flanges.

So no Cans on tonight - GRRRRR.

But will return!