pics wanted for cutting the head

[(F5)]

yeah my local kart guy uses one & I read one of the top ex Aprilia GP guys saying he uses one so it was a clear indication that it was a good idea. So far on my race engine I found I was getting huooge leakage on a cylinder that was producing good but not spectacular power & polishing the bores.

this sort of thing. heaps of howtos on Youtube.

http://www.harborfreight.com/cylinder-leak-down-tester-94190.html

I built a 2 stroke leak tester many years ago which checks for crankcase leaks, but this type above is purely ring seal.

 

[Jakobi]

Geesh thats a cheap one. Its always been the price thats put me off. That and I don't have an air compressor to fill it with. Haha!

I have no doubt they are a good thing to test for ring sealing. Even better on the 4T though as you can identify how much compression you are losing either past the rings, or the valves.

 

[(F5)]

Valves? Heresy!


Yeah I was surprised at the cost, but landed in NZ for $113 (I ebay'd one) which is probably equv of $14.98Aus.

Don't have a compressor? You can run one of these with a $100 cheapy + blow up tyres & more importantly use the blow off gun to blow through jets, clean off debris & a million other things.

treat yourself.

 

[Jakobi]

Oh I've been eying them off for some time but can't commit to a cheap one. Then next thing I'm looking at thousand dollar units and I can't commit to that coin to blow out jets and dust. Caught in a 22.

 

[gasmonkey]

Get the cheapie,they're great.
I've got both.The 2.7hp unit is good with drills,chisels,sanders etc.
The little cheapie gets used heaps.Pumps up quick for those small jobs.

 

[(F5)]

totally agree, the smaller one got used heaps more than the bigger one so it isn't a waste of money. You can even drive an impact wrench off it in small doses. Just don't try spray paint or die grind.

 

[hannesd]

so, i just measured the cc's in the head before i go and cut it.
squish was 1.83mm (with a base gasket that measured 1.45mm?), going to reduce the squish to 1mm.
head volume was 16cc and i may bump that a tad up.
curious how much head volum?e would decrease when i only machine the head.
going to try to measure that, even if it's just to satisfy my curiosity (and yours) :-D
to adjust the head volume, i'll probably just make a flat surface around the spark plug hole to increase head volume, and not reshape the whole bowl.
like this pic :
http://www.gasgasrider.org/forum/attachment.php?attachmentid=2948&d=1358200176 .(was posted before in this thread)

wish me luck !!

 

[Diggs345]

Good luck , did you make a mandrel , you want something like this

 

[Jakobi]

so, i just measured the cc's in the head before i go and cut it.
squish was 1.83mm (with a base gasket that measured 1.45mm?), going to reduce the squish to 1mm.
head volume was 16cc and i may bump that a tad up.
curious how much head volum?e would decrease when i only machine the head.
going to try to measure that, even if it's just to satisfy my curiosity (and yours) :-D
to adjust the head volume, i'll probably just make a flat surface around the spark plug hole to increase head volume, and not reshape the whole bowl.
like this pic :
http://www.gasgasrider.org/forum/attachment.php?attachmentid=2948&d=1358200176 .(was posted before in this thread)

wish me luck !!

Deck height volume = (use this calc with a Radius of 31.25mm, height is your squish height. IE how much the piston sits above the cyl. Your result will be cubic mm which is same as ccs.)

So if you shave 0.83mm of material from the head, using the calc above, will result in a reduction in volume equal to 2.54743cc

Just confirming. Did you just measure the combustion chamber volume (head volume) or the entire trapped volume? Its the trapped volume that will determine the uncorrected compression ratio. The combustion chamber volume is just a part of the formula.

 

[hannesd]

so euhmm i chicken'd out about cutting the head.
i was talking about this to some local riders and they said i had alot of guts doing that .
they said, what of you screw up your head? yeah, true...not an easy thing to find a replacement.
so i just put 'er back together without any base gasket. just some liquid gasket.
started up just fine, went for a ride just now, more torque available,good idle.
maybe try a smaller PJ (now 45).
she doesn't really rev very high, but then again, neither did before...
maybe a smaller MJ (now 180). or play with the needle.
been thinking about timing, haven't checked before.

anyway, happy sofar good to start our season here
maybe next winter might take'er on for real then.

ciao, Hannes.

 

[hannesd]

so after the adjustment (no base gasket) the gasser ran rich off idle.
so i swapped the 45PJ tot a 42.
MUCH better now!!
feels like it's running smoother all over the revs.

tomorrow i have a day drive planned.
allso changed gear oil. i mixed 50/50 5w30 engine oil with atf oil (dexron III H)
i'll report back after the ride.

ciao, Hannes.

EDIT : so here goes the (short) ride report.
the bike runs very strong compared to previous setting.
strong bottom as can be expected from a 200, good mid power, bit short up high in the revs.
idle is allright but not as i want it, might go even 1 step leaner from 42 to 40.
to try to clean up the top revs i might try allso a leaner jet, from 180 to 178.

about the gearoil i mixed, it's k but not as good as it should.
i can start in gear but it drags,smooth shifting is ok.

ciao, Hannes.

 

[(F5)]

so euhmm i chicken'd out about cutting the head.
i was talking about this to some local riders and they said i had alot of guts doing that .
. . .

Meeow


Actually I was thinking I must get around to it myself (as I descended down a nice tight forestry section in the weekend, maybe that's why I'm slow in the tricky stuff, brain is off thinking about all sorts of random stuff), it's been about 8 months since I put in a new piston & didn't have the spare time & haven't since with other projects on the go (including modifying heads on other bikes on my 1940s lathe).

 

[andy176]

Can this b done on a 300? I just bought one that I want to supermoto and think its gona b abit short on power? I have a lathe but prefer not to touch the concave wat results/problems would u expect just by machining the mating surface and is there a standard amount to remove?

 

[hannesd]

Can this b done on a 300? I just bought one that I want to supermoto and think its gona b abit short on power? I have a lathe but prefer not to touch the concave wat results/problems would u expect just by machining the mating surface and is there a standard amount to remove?

i'd say, just measure you current squish and go from there.
if it's excessive like over 2mm, you could do the same as me, leave the base gasket out and use some liquid gasket.
not sure many others would do the same but mine just woke up by doing that !!! (ec 200 with squish now at 1.35mm instead of 1.85mm)

ciao, Hannes.

 

[andy176]

Cheers for the reply. Wats the easiest way to measure the squish and wat roughly should it be? Bike had a piston kit fitted before I bought it. I'd b happy enough to try wat u have done it would mean not having to touch the head or take very little of it. Can the base of the barrel not b machined to save touching the concave part of the head?

 

[(F5)]

if you're going to SM it you don't really want to drop the barrel. in fact you may want to raise it till the ex floor is level with the piston at BDC from previous posts for good top end.

Then decide what gas you are going to run & that could help decide what compression you want to go to. There is heaps of info on the web to help with this decision.

Seriously if you want to maximise power then it is worth a little effort for this type of power gain, that is improving the efficiency throughout the range.

measuring a big cylinder is easy, do a google on how to & maybe there will be a youtube 'how to' for 2 strokes.

Cutting the cylinder head isn't that difficult, but you need to learn in steps. I'm a muppet with a 1940's Sheldon lathe & old style tooling & never really learnt how to properly grind a cutter, but I ended up with a nice curved shape & with some care can remove a bit from the dome & make it match ok. Then finish off with sandpaper (carefully can stick some paper on a shape).

 

[hannesd]

i'll see if i can find an old cil head to practice and later on get my 200 done afterall, see what's more to gain