What's on your bench?

[EFSM]

Currently on my workbench: a reed valve block for cylinders with a round intake. The base is currently a Husqvarna 372. However, the block should fit many other chainsaws or be adaptable. There's still quite a bit of work to do.

The reason for reed valves?

 

[Roschdworschd]

The reason for reed valves?

Asymmetric timing

 

[Shane¹]

Got lots of new projects today. I don't think this one 350 has ever cut wood. Got lots of pressure and vac tests to do lol

 

[stretch5881]

Very nice! Is that a '72?

I remember the days of getting hosed on insurance. I had a '66 Corvette, 425 hp 427, 4 speed, 4.11's, knockoffs as my daily driver in New Orleans in 1995-1996. I was paying $400/month in insurance.

Yup. '72 Rallye. Only made 1 year and took the place of the R/T. I'm lucky it wasn't my tombstone.

 

[president]

Rebuilt a close ratio T-10 for my budget '72 Javelin endurance race project (24 Hours of Lemons). Now I need to build a backup trans.

View attachment 481808

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love the lil pacer in background aka the greenhouse!

 

[EFSM]

Asymmetric timing

Are you adjusting the port height or timing a bunch and then using the reed valves to prevent blowback?

 

[Roschdworschd]

Are you adjusting the port height or timing a bunch and then using the reed valves to prevent blowback?

That is the idea

 

[oddsaws]

Rebuilt a Mikuni carb for a Yamaha four wheeler for my wife’s boss. This was my barter for machine work

 

[jacktheripper]

P52

 

[oddsaws]

Ms400 on the bench today. Low compression

Follow up:

The owner of this saw said it was running erratically a few weeks back. Compression tested good, pressure and vacuum good. Pressure tested the carb and it checked out. I don’t work on m-tonic too much so I suggested maybe we try a new solenoid. Replaced the solenoid, put a bar and chain on and made about 5 cuts. I didn’t bury it to the dawgs or anything. Sent it on back.

This week he says his guys ran it for a while and it shut down. No compression.

looks like a piece of the piston/ring came off eventually.

Currently stumped on a diagnosis.

Here’s the damage:

 

[singinwoodwackr]

 

[singinwoodwackr]

Follow up:

The owner of this saw said it was running erratically a few weeks back. Compression tested good, pressure and vacuum good. Pressure tested the carb and it checked out. I don’t work on m-tonic too much so I suggested maybe we try a new solenoid. Replaced the solenoid, put a bar and chain on and made about 5 cuts. I didn’t bury it to the dawgs or anything. Sent it on back.

This week he says his guys ran it for a while and it shut down. No compression.

looks like a piece of the piston/ring came off eventually.

Currently stumped on a diagnosis.

Here’s the damage:

View attachment 482222

View attachment 482223

No air leaks before you tore it down?

 

[EFSM]

Follow up:

The owner of this saw said it was running erratically a few weeks back. Compression tested good, pressure and vacuum good. Pressure tested the carb and it checked out. I don’t work on m-tonic too much so I suggested maybe we try a new solenoid. Replaced the solenoid, put a bar and chain on and made about 5 cuts. I didn’t bury it to the dawgs or anything. Sent it on back.

This week he says his guys ran it for a while and it shut down. No compression.

looks like a piece of the piston/ring came off eventually.

Currently stumped on a diagnosis.

Here’s the damage:

View attachment 482222

View attachment 482223

The question is this: Did the ring break before or after the other damage? It looks about like there is some damage from pre detonation, but maybe that’s all debris damage.

 

[oddsaws]

No air leaks before you tore it down?

Yeah it’s definitely got an air leak around the base gasket flywheel side. Just wondering if something maybe blew up first

 

[hacskaroly]

Yeah it’s definitely got an air leak around the base gasket flywheel side. Just wondering if something maybe blew up first

Is there any carbon/gunk build up under the rings? I wonder if there was then its possible it would not let the ring retract all the way allowing it to catch on an opening and snap off the bits.

 

[EFSM]

Yeah it’s definitely got an air leak around the base gasket flywheel side. Just wondering if something maybe blew up first

I thought you said you had pressure tested it and it was okay.

 

[oddsaws]

I thought you said you had pressure tested it and it was okay.

To clarify - it pressure tested okay last time I had the saw on the bench

 

[Tor R]

Follow up:

The owner of this saw said it was running erratically a few weeks back. Compression tested good, pressure and vacuum good. Pressure tested the carb and it checked out. I don’t work on m-tonic too much so I suggested maybe we try a new solenoid. Replaced the solenoid, put a bar and chain on and made about 5 cuts. I didn’t bury it to the dawgs or anything. Sent it on back.

This week he says his guys ran it for a while and it shut down. No compression.

looks like a piece of the piston/ring came off eventually.

Currently stumped on a diagnosis.

Here’s the damage:

View attachment 482222

View attachment 482223

I don't think it's a leak that caused the saw failure, now I only know about the pictures that have been posted, but the damage to the piston ring has been there for a while, carbon build-up there according to the pictures.
I also don't like so much soot deposit down the piston....
Of course it could be that it had started to have an air leak after you measured the p&v, but this chainsaw was well on its way to breaking down, with or without an air leak.

 

[singinwoodwackr]

I don't think it's a leak that caused the saw failure, now I only know about the pictures that have been posted, but the damage to the piston ring has been there for a while, carbon build-up there according to the pictures.
I also don't like so much soot deposit down the piston....
Of course it could be that it had started to have an air leak after you measured the p&v, but this chainsaw was well on its way to breaking down, with or without an air leak.

With that much blow-by and for so long I’d think both rings were stuck to some extent.

 

[singinwoodwackr]

More better now