A Tail of Two–MS200T–Top Handles & Compression Tests

[openspaceman]

23 minutes ago, spudulike said:

I was saying to measure the ring in different areas around its circumference to compare the thickness but was trying to say the thickness between the outer surface that contacts the bore and the inner that butts up to the bottom of the piston groove and not the height of the ring as if you laid it flat on a table! Ring wear will give too much end gap and will effect compression.

Yes I understood this after your last reply. As I said it's not something I have ever done as the first thing to show up would be the large ring gap which would mean a new ring either way.

 

23 minutes ago, spudulike said:

 

Nikasil can wear due to ingress of fine woodchip, seen a few but not common.

Yes, Nikasil is hard and only .4mm thick I think. It was cast iron bike engines we used to check the ring gap in several places down the bore to decide whether a rebore was necessary. In those days british bike engines seldom lasted 50k miles without a complete rebuild.

[arborlicious]

Pulled the old girl apart and I'm pretty sure the cylinder and piston are in good condition? Have yet to check the rings for wear.

 

[spudulike]

Looks OK from what I can see.

[arborlicious]

On 11/06/2018 at 06:09, spudulike said:

Looks OK from what I can see.

Was hoping you'd concur. Hopefully I'll have some new caber rings by the end of the week.

 

Now to open up a can of worms...

Do you do any machining of deck and or cylinder on your refurb saws to increase compression? Or just lose the base gasket and use a thin coating of sealant? Is this worth doing without additional porting? (to fix up the timing) I searched the Porting and Tuning Thread but could only find information on some of your husqvarna jobs.

 

[spudulike]

Just drop the base gasket, the extra compression makes up for the shift in timing figures!

[arborlicious]

On 13/06/2018 at 06:27, spudulike said:

Just drop the base gasket, the extra compression makes up for the shift in timing figures!

Excellent. Sounds all too easy. Still waiting on the new rings.

 

In the mean time, thought I'd do compression tests on some more saws. Here are the results (all cold at about 1,000m altitude.)

 

MS460 160psi

MS261C 160psi

MS461 150psi

MS661 135psi 

395XP 150psi

 

MS201TCM 100psi

 

These saws all start and run well so the MS201TCM result seems out of place. Although I did have to use the small adapter for the 10mm spark plug hole but I can't see how it would lower the compression too much.

 

I'm going to compare some of those with results my mates saws (MS661 and 201T.)

 

[spudulike]

That 661 looks low to me, most well used saws will pull 150, lightly used ones around 170 but will depend on altitude and the gauge being used. The small gauge does knock a fair bit off and can be misleading, I tend to get around 20psi drop using it - the reason is that the void in the adaptor has to be filled with air before the meter starts reading so in effect, makes the combustion chamber volume bigger and lowers the reading.

[arborlicious]

9 hours ago, spudulike said:

That 661 looks low to me, most well used saws will pull 150, lightly used ones around 170 but will depend on altitude and the gauge being used. The small gauge does knock a fair bit off and can be misleading, I tend to get around 20psi drop using it - the reason is that the void in the adaptor has to be filled with air before the meter starts reading so in effect, makes the combustion chamber volume bigger and lowers the reading.

Ah, understand now. So on a tiny combustion chamber like the ms201tc the adapter would have a noticeable effect. 

 

[spudulike]

Yes as you have an extra void to fill within the adaptor so the compression will never read as high through when using one.

[arborlicious]

Got the new rings yesterday along with a mityvac for doing vacuum and pressure tests.

 

Do you have a simple method for blocking the intake without having the handle installed (in order to screw onto carb mount? Maybe a rubber bung in the intake boot?