Measuring squish on my MS200T

[MattG]

Hi people,

So I went about setting/checking the squish band on my latest 200T. Before I measured it I noticed slight carbon build up on the top of the jug, which after quickly polishing off I noticed some strange artefacts, basically very slight raised areas around the edge....which (on another forum) I was informed are due to the bosses (or something) inherent in the casting process. You can see them right here:


These peripheral areas are detectable with your finger nail, and seem to protrude out by a fraction of a mil.

Anyway, seeing as the squish I approximately measured with the base gasket fitted was around 0.040", I decided to remove the gasket, and measure it more accurately with 4 pieces of solder, pushed quite close to the edge i.e.



You can see on the pic above that solder is squashed more at the periphery when moulding marks protrude. Note that this slightly protruding area is about 2mm wide (except those 4 D-shaped areas which must be ~4mm).

When I measure the 4 pieces of solder, I'm seeing about 0.013-0.014 for the areas where the moulding bosses protrude, and about 0.021-0.022 in the main part of the squish area.

What to do? Should I accept these annoying protruding areas and add 0.005 of gasket....or given seeing as the engine is only 35cc and that the protrusions are right near to the edge, ignore them and just run it like this?

All advice appreciated, Matt

 

[Mastermind]

Moving this to the saw forum.

Welcome to OPE Matt.

Excellent post sir.

Those casting flaws is the reason I prefer a machined squish band over a pop-up type piston.

.013 is a little too tight in my mind. So, I'd add a beer can gasket at least.

 

[MattG]

Moving this to the saw forum.

Welcome to OPE Matt.

Excellent post sir.

Those casting flaws is the reason I prefer a machined squish band over a pop-up type piston.

.013 is a little too tight in my mind. So, I'd add a beer can gasket at least.

Thanks for welcome MM!

Yes those flaws, whilst being quite regular, are damn annoying for giving that irregularity to an otherwise nice measurement. If I'd not cleaned it up - I wouldn't even have seen them.

Yo, I'll take your advice, though I might go for something a tiny bit thinner e.g. magazine paper (one of the wife's, while she aint looking!). But yeah 0.013 did seem too tight to me.

I'll let you know how I get on.

 

[Mattyo]

beer can is .004" .... I'd 2nd that suggestion

 

[MattG]

beer can is .004" .... I'd 2nd that suggestion

For sure, you're right there, Matt.

But, I'll be honest now, and admit that I hate cutting that stuff up. (I spent half hour yesterday making a "ring compressor" from can material.....in the end I still ended up just using fingernails as ring compressors....the best possible tool for that job, IMO).

Anyway, I'm going measure up some paper and card over the next day or so, and have another go.

 

[smokey7]

When you go yo cut your holes for the bolt holes. Clamp the gasket between two pieces of wood or sheet metal. That way when u drill through it wwnt tear. Also if its thin you can take a chamfer bit to a small piece of hydraulic tubing to make a hole punch just use it on something soft as a base to punch thru like wood.

 

[TreeLife]

Ole Dom likes to use plasti-guage for measuring things like that ;-)

Measure a piece of construction paper for thickness...might be a good course too

 

[TreeLife]

Ps nice post and welcome to ope!

 

[Al Smith]

The solder won't be entirely accurate because the piston will tilt a little bit .Close enough I suppose .Normally a Stihl base gasket is around 20 thou thick .

If I recall the 200T I put the soup to was around 36 thou stock but again that could varey a bit .I took it down to 22-23 thou .
Fact I cut too much off the base and had to improvise with a thicker base gasket .Worked--all that mattered .

 

[Mattyo]

Beer can cuts with fine scissors...and use a hole punch for a 3 ring binder...works fine for the bolt holes.

 

[Mattyo]

Oh....don't don't don't use thick card stock with one glossy side.....

Don't ask

 

[Wood Doctor]

Something OP forgot to mention. Rebuilding the top end of a 200T is quite an exercise. Stihl did a great job of burying this cylinder, the muffler, the intake manifold, etc. Good rainy day project to say the least.

 

[MattG]

When you go yo cut your holes for the bolt holes. Clamp the gasket between two pieces of wood or sheet metal. That way when u drill through it wwnt tear. Also if its thin you can take a chamfer bit to a small piece of hydraulic tubing to make a hole punch just use it on something soft as a base to punch thru like wood.

Now that is a mighty fine idea! Thank you.

Beer can cuts with fine scissors...and use a hole punch for a 3 ring binder...works fine for the bolt holes.

Yup, that's another good one.

The solder won't be entirely accurate because the piston will tilt a little bit .

My theory is that by having 4 pieces spaced equally on the crown, tilt should be minimalised.

Something OP forgot to mention. Rebuilding the top end of a 200T is quite an exercise. Stihl did a great job of burying this cylinder, the muffler, the intake manifold, etc. Good rainy day project to say the least.

Yeah, they're certainly fun. This is my second one. And everything's so diddy. I guess I get off on these masochistical tasks. The trickiest thing on the top end is the piston pins, closely followed by the rings; the small bores make them hard to get ones finger nails squeezing them in all the right places.

I try to make things easier by crafting "tools" where possible. My best recent one being a wooden stay to hold the piston upright, above the engine base. (You can obviously pay stihl for one too if you like ). Regardless, things like that make the job much more satisfying.

 

[Mattyo]

Something OP forgot to mention. Rebuilding the top end of a 200T is quite an exercise. Stihl did a great job of burying this cylinder, the muffler, the intake manifold, etc. Good rainy day project to say the least.

I disagree, and you can watch me do it bolt for bolt on youtube so its not so intimidating.

 

[Tor R]

Welcome to ope Matt!

 

[Al Smith]

To reiterate about that solder .It's not entirely necessary to have micron size measurements ,close is close enough and solder works good enough for that .
Fact I doubt seriously if you made the head deck/piston clearance to 21-25 thou if it would make that much diff in how it ran .

 

[MattG]

Quick post from me cos it's feet up time for me now in the UK. I found me a thick paper flyer (well I pinched it from the work's canteen ), which comes in at 0.1 mm (~4 thou). This is perfect as with a tad of compression should still bring me up to about 17 thou clearance in the tightest areas.

And to punch the holes my wife saved the day as usual - she found this thing that she uses for punching belt holes - joy of joys, one of the sizes, being 5mm.

And below I'm hoping that a picture tells a thousand words....



later Gentlemen

 

[Al Smith]

An alternate method is using short pieces of varies size steel tubing for a punch .Sharpen the edge and punch away .FWIW I've made gaskets for carbs with this method .

 

[huskihl]

Spent .223 or .243 casings make for a nice punch also

 

[MattG]

An alternate method is using short pieces of varies size steel tubing for a punch .Sharpen the edge and punch away .FWIW I've made gaskets for carbs with this method .

Nice!