MattG

Ha ha!

I'm still after OEM.....cos whatever "artefacts" I get to in my life...I wanna make damn sure they're OEM ones!

back!

Yeah, I know what you mean re. the timing wheel and then bringing the Meteor to spec. I don't have an old 460 jug to compare too, however! But on ope-forum mastermind has posted those degrees somewhere....

The thing that makes me most nervous with the above approach is the transfers, since ideally, I'll need a right-angle attachment for my grinding tool. Now I did see some RA dremel attachments on amazon, eg.

(hmm... tried to embed the amazon link right here, but after about 5 tries I gave up fighting arbtalk's mental message formatting algorithm!!)

but on the questions and answers there was much vagueness as to whether the above can be received by the flexidrive shaft.

So I guess I'll wait for a bit longer for good 2nd OEM jug to "materialise".

Take a butchers at the pics in this thread:

My Buddy Dave's MS260 and an AM vs. OEM Jug Comparison | Outdoor Power Equipment Forum

They are not good advertisements for AM quality.....you get what you pay for!

The QC on the intake port for meteor on post #4 is horrendous.

Try the Meteor one for around £80.00, it will do the job and are made well - very hard plating!

I'm bearing the meteor option in mind. But I'm curious about the differences in porting between the OEM and meteor. For example are the heights, weights, angles identical?

You may remember from a previous discussion re. casting artefacts on the top of a head on a 200T to know that I'm somewhat of a perfectionist!! I'm not going to all the bother of putting together a 44/46 hybrid etc. and then failing to hit the max. possible with a reduced port areas.

If the meteors porting figures are on the nose, then cool, else I'm continuing my search!

thanks Matt

Yes, I know that they are rare as rocking horse sh!t, however......has anyone got a decentish 460 cylinder they want to part company with in exchange for local currency???

I think it will be good too. Update when it's done please.

 

 

DT's, that brings back some memories. I had a secondhand125 air cooled that came with an aftermarket exhaust. On / off power band, noise, blue smoke, piston slap - come to mind. Happy days.

 

There a rule about exhaust port width vs cylinder diameter. I wonder whIch side of the line your DT was

 

bmp01

Yup, I'll certainly keep you updated.... I've just very carefully taken off ~0.5mm of the exh roof. Much trickier than my old Yammies (mine was air cooled too - DT175MX - cracking bike), and now the jug's all slapped back down with a slip of sealant (instead of the stock gasket). I'm gonna give it a final press/vac test, though I can't see why the base wont seal pretty nice as is, but just to be sure.

I probably won't touch it for a little while now, plenty more things to do round here alas. But I'll get a youtube of her running when it's all good.

I think I'll be good

I'm not trick enough to dare to touch the transfers, and the gasket delete will have increase inlet duration already.

10-4 on what you said re. the CR, however at operating revs. the actual cranking pressure will be different.

I've done this stuff before like 25 years old on MX bikes, widening ports (in my humble opinion) is more contentious, since you can run into ring bulge issues. Experienced this myself, when I made my Yammy DT175's exh too wide. F**king blistering performance, but destroyed piston and rings every 400 miles!!!

I know what you mean on the safety thing. Even a small saw can kick back nasty on a misfire at start time. FWIW I always cold/hot start anything with the chain break on, I've got a pretty face and I sure don't want it scratching!!

Well, the next job, is that given that I've lowered the cyl by 0.5mm by the gasket delete....the next thing is to raise the exhaust port roof by the corresponding value - I'm not after higher revs - just perfecting the specification of things as much as I can. And hopefully maximising the torque output.

A couple of piccies as promised:

Firstly here's the setup rig to machine the squish band.....started on P80, then worked down to P240. Secondly, after a few minutes grinding, managed to rid the squish band of those stupid manufacturing artefacts, and hey presto, now have a proper squish.

It's Shed tuning, Spud Not commercially viable granted, but fun for those that enjoy that sort of thing.

 

But in fairness if you can run the piston up close to the squish band it will reward you with a little bit of extra oomph but more importantly an all round nicer engine. The turbulence you can get from tight squish is underrated IMHO, a more dependable / reliable combustion process due to the extra gas movement, so even if the mixture isn't spot on (it never is, through the whole rev range) - combustion will be better. So hopefully a more crisp engine response. Just makes the saw nicer to use. Innit....

 

Starting it might need a bit more care though, especially a top handle saw like this one - you listening MattG?

 

bmp01

Ha ha! You wanna try drop starting my 064 on a cold day, cos it aint got a decomp......so the 200 with raised comp will be a piece of p!$$ !

But yeah, getting squish right, also means more of the fuel/air charge will be confined to the actual combustion, and yes, thats the crucial detail.....not just a marginal compression ratio increase.

Matt

I done the "machine the top of the dome" trick using a old piston with disc of emery stuck on top, as suggested by bmp01. Have to say, it was a lot easier than I thought, and I reckon I've got a pretty squish clearance without the base gasket now, rough measurements being between 0.45 and 0.55mm in the 4 different measurement points. Will try to get some piccies up in the next day or so.

Got any double sided tape? You want the stuff that is just a bit thicker than normal sellotape. I've got some made by 3M and some used for carpet laying, both work. When you need to remove it, use heat.

The key here is a uniform thickness of what ever you use to hold the paper.

 

Yeah, i understood how little you need to remove. I don't think you even need to go very coarse (200 grit?) but cleaning the paper and cylinder regularly to stop it "plugging" will help.

 

And of course none of this is worth it if you make a mess of the cylinder bore so keep the bore and piston OD clean. And keep the paper away from the edge of the piston, say 1mm minimum in from the edge.

 

Just my 2 pence worth....

 

bmp01

Dude,

Missus has caught some double-sided taped she reckons.

I've got fine paper already, but I've requested that 800, 400, 240 is purchased, and I'll see how things pan out.

10-4 about keeping it clean!! I never ever want to repeat the exercise of my late teens, where not having any valve grinding paste, led me to mixing sand with grease, and unfortunately getting the odd grain between the valve stem and guide. You live and learn it seems

Your comment re. "1mm from edge" Hmm..... unfortunately the crappy moulding extends right to the edge, so it will be flying on the seat of my pants type of work. I've done worse in the past - so I'll just have to play to cool.

later fella

Ha! Yeah they are little sods to get "just right". I personally use my own version of the one in the manual for the L side of the tune, but seeing as I'm not up in a tree all day long, I'm probably not as fussy as some over the exact throttle response!

So get a bit of sandpaper stuck on the top of the old piston, spin the piston with a bit of wood. 5 mins and those protruding lumps will be gone. Use the existing squish band to guide you in your progress. You're not afraid to get in there and clean up the combustion chamber, this isnt much different. In both cases very careful cleaning required. ...

 

bmp01

That's a good idea. Any thoughts for holding the paper down though? I'm thinking superglue, since I'll probably want to start coarse and work down finer.

Do appreciate that those things you describe as "lumps" merely look that way when viewed on a screen, they actually protrude down no more than that thin ring, the very very outermost annulus - of about 2mm which you should be able to just make out by viewing my piccy. They are merely D-shaped bosses on the existing casting process artefact (for want of better terminology). The entirety of those things you refer to as lumps and that very very outermost ring on the dome, all do protrude down by about 0.15mm into the cylinder, repeating myself, into the available squish clearance space.

Sorry for waffle! But yeah, the paper idea is a good idea - and I'll keep you posted.

Matt

Yeah, Dremel isnt a precision tool, i was assuming you'd blend to surrounding to create clearance not an exact squish number.

Have a look at Mastermind's squish machining technique on Arboristsite. He uses a single profiled cutter mounted on a sustitute piston that closely matches the bore size. .... hand operation IIRC. Or for the material you need to remove - sandpaper mounted on the end face of a piston / sustitute piston (end face or piston not flat).

 

By the way, are the 4 lumps lower than the squish (that really would be carp) or is the piston domed?

 

bmp01

Finally, I found a 0.1mm (4 thou) thick flyer at work. Pinched it. And made me a replacement gasket.....with a razor blade and belt hole puncher as my cutting implements. Using this (instead of the stock gasket) should give me ~17 thou at the crappy periphery where those stupid bosses are, and about 26 in the area without that sh!te.

Ta da!

Yeah, Dremel isnt a precision tool, i was assuming you'd blend to surrounding to create clearance not an exact squish number.

Have a look at Mastermind's squish machining technique on Arboristsite. He uses a single profiled cutter mounted on a sustitute piston that closely matches the bore size. .... hand operation IIRC. Or for the material you need to remove - sandpaper mounted on the end face of a piston / sustitute piston (end face or piston not flat).

 

By the way, are the 4 lumps lower than the squish (that really would be carp) or is the piston domed?

 

bmp01

Yes, man. And that was my precise issue. They protrude (along with the rest of that crappy ring around the periphery of where the jolly old squish should be) by about ~0.15mm. Which scuppered my otherwise tasty measurement of 0.55mm I got for normal area (away from that stupid moulding artifact). Growl!

It should be, it's a machined band, cut at the same time as the boring opertion.

Disappointing to hear the combustion chamber of MattG's 200T has lumps in it, presumably in board of the machined squish. Time for Dremel work?

 

Equally disappointing the squish is in the 1.0 mm range, poor effort.

 

bmp01

Dremelling it would be nigh on impossible I think to get it right. A pro tuner would lathe it away I guess.

I'm not that perfectionist....and of course after losing the stock base gasket and then shimming out, with a custom paper/tin-can gasket, we probably take me to about 18 thou under the molding flaws and 26 in the regular part of the band.

But yeah, you're right bmp01, 1.0mm for a STIHL oem cyl is rubbish, and I've expected them to machine away the molding bosses.......

I'm glad I cleaned the dome first now, else I'd have never known.

Well yeah, it is. It's the outer annulus of the combustion chamber......However the way that lots of cylinders are manufactured is that the bosses from which the casting are left and protrude into the depth of the chamber by up to 0.15mm which perturbs the squish (you can see it on the very outermost part of cylinder combustion chamber). You wont see this typically - unless you polish the roof of the dome prior to measurement.

A higher quality of manufacture would machine away this detail leaving a consistent band.

So the "artefacts"

are those imprints around the periphery of the combustion chamber outer dome (first pic). And they protrude into the CC, by 0.15-0.2. Very annoying. As you have to shim out to give them clearance and that makes the regular squish's clearance bigger than needs be.

The cyl is the OEM Mahle/Stihl. So its a shame they don't lathe these flaws, call them what you like, off after the cast.

Have you ever seen them before?

Matt

Whats a casting artifact ? Could you take it on the antiques road show ?

Hey Stubby,

Firstly - ha ha!

Secondly - I'm not at home, so tell me if you can see the image here:

Measuring squish on my MS200T | Outdoor Power Equipment Forum

and if so, you'll see what I mean. They are from the casting mould, and are very annoying in squish setting.

If you can disable the accel circuit perfectly and no air leaks remain, and the rest of the carb is good, then suitably adjusted, there will be no differences and you should have a good carb as a result.

When I first roughly measured the clearance it was about ~1mm. Discovering that the base gasket is 0.5mm thick I discarded that, and after polishing the roof of the combustion chamber, I discovered casting artefacts (I'll post an image when I'm next home), which reduce the squish around the periphery. Accounting for these, gave me, between 0.34mm (under the artefacts) and 0.55mm in the main area.

So I'm looking shim out a tad by about 0.08mm. I'll keep you posted.

I thought I'd share the saw mechanics I did the other day. I decided to get the squish set aswell as I could on my 200T. The measuring process works as follows.

First remove the cylinder, and glue using some grease 4 pieces of 1mm thick leccy solder.

Lob the cylinder back on. Note that I previously marked on the cyl and the fly wheel reference point so that I could get to TDC quickly.

Move the f/wheel and thus the piston a few degrees past TDC, then back a few several times to get the solder squashed.

Remove the cylinder, and carefully measure (micrometer or vernier calipers) the solder where it was squashed. The figures should give you an indication of your clearance.

Hope this helps someone.

Matt

The 200t's I own earn me my living. I tried being a cheap skate & bought cheaper carbs, had the accelerator pump blanked off etc, but in basic terms the saws underperformed & I continued to have issues. Now I just rebuild the carb once then replace with an OEM one. They all work as they should & earn my my wages. Simple maths for me

I agree I bought a cheapy carb once (yes after blocking the accel pump channels with JB weld).

I couldn't tune it on the L-side right, it worked, but wasn't nice....so I forked out on a STIHL one, this is the one without the accelerator pump

1129-120-0650 /Zama C1Q-S32

and for me it worked a dream

Those cheap AM carbs won't have the accel pump. It's more money to produce. The accel pump seems a bit overrated for the later problem which can be caused.

If the L-side of the carb is setup how the manual explains you should still get good throttle response and hot starting. If it was a decent cheap carb that is.....