What's on your bench today?

[spudulike]

On ‎18‎/‎11‎/‎2018 at 10:24, bmp01 said:

Pistons are forged (not cast).

You need to look for the classic signs of fatigue failure to identify where the failure started - if you can be bothered. Its where a crack exists while the part are deflecting and rubbing across the crack surface,  causing a distinctive pattern, often crescent shaped. This happens while the engine is running and can be hundreds of thousands of engine cycles. Bits that shatter during the last few hundred revs don't have that appearance. Trouble is most of the evidence is often destroyed by subsequent impact damage.

 

What's a strato flange and what does it bolt to ? Barrel? 

On the MS461, there is a strange alloy bracket that bolts across the crankcase mouth and goes right up in to the piston. There has been a lot of speculation on what it does but the clever money is on dome sort of diverter creating a strato effect on a relatively standard engine design. See pic below.

I believe that the piston probably had a very fine crack in it after I tried to remove the central boss from the clutch after an employee of the saws owner didn't fix the e clip on correctly. The clutch grenaded and did the boss up super tight. I used pretty much all the force I could muster to shift it and ground it off in the end with a diamond burr after I couldn't shift it - it lasted a few months before letting loose. The stop I used was the Stihl one followed by rope when the damn thing didn't shift.

Got it back together again and hope it lasts now, all the parts looked good and measured OK but it is damn difficult to tell if components have micro cracks or a bit of stress damage. I know a few tricks in checking engine components and agreed with the owner that the repair bill was worth paying to see if it lasted - the other option was a complete rebuild with new components which didn't make sense.

 

[spudulike]

1 hour ago, billpierce said:

My beloved 361 started playing up today. Kept pulling the starter out my hand and is behaving like an 064. Starting has really hard and seems to fire early and RIP the starter out your hands. Did manage to start it but didn't feel like it was revving up proper job.

Piston is well. There is a slight playing in the flywheel woodchuck. Perhaps it has slipped slightly. Tried adjusting it and was easy to pull for a few pulls. Then back to tough.

Disappointingly it seems the woodchuck key is forged into the flywheel rather than a replaceable part. So there goes 80quid.

Anyone got any advice or anything to check before I shell out?

Turning the flywheel the bearing did feel a bit lumpy like a 50p rather than super smooth, again dont know if that's super bad?.

The term is "Woodruff" and yours looks 100% fine. It is quite usual to get a couple of degrees movement in the flywheel and is of no concern. If the woodruff key is sheared or missing, then you have a real issue.

The facts are the ignition seems to have gained advance - how........my bet is either the flywheel to coil gap is too large or the coil has gone bad. I did have a 361 in once where the thing would only rev to around 7Krpm and a new coil sorted it out.

If you want to try to manually retard the ignition a few degrees then opening up the spark plug gap to 2 -3 times the original gap and opening up the coil the flywheel gap will do this but reckon your fault is probably the automatic retard circuit in the coil has failed giving full advance from low revs.

[billpierce]

1 minute ago, spudulike said:

The term is "Woodruff" and yours looks 100% fine. It is quite usual to get a couple of degrees movement in the flywheel and is of no concern. If the woodruff key is sheared or missing, then you have a real issue.

The facts are the ignition seems to have gained advance - how........my bet is either the flywheel to coil gap is too large or the coil has gone bad. I did have a 361 in once where the thing would only rev to around 7Krpm and a new coil sorted it out.

If you want to try to manually retard the ignition a few degrees then opening up the spark plug gap to 2 -3 times the original gap and opening up the coil the flywheel gap will do this but reckon your fault is probably the automatic retard circuit in the coil has failed giving full advance from low revs.

cheers spud. dont know where i pulled woodchuck from, long day.

 

perhaps that 361 you mentioned was mine? you did my coil about 3 years ago, so would be pretty disappointing if its failed again. i'll try giving it a bit more gap. thats pretty good news if that sorts it.

 

 

 

 

[Ratman]

On the MS461, there is a strange alloy bracket that bolts across the crankcase mouth and goes right up in to the piston. There has been a lot of speculation on what it does but the clever money is on dome sort of diverter creating a strato effect on a relatively standard engine design. See pic below.
I believe that the piston probably had a very fine crack in it after I tried to remove the central boss from the clutch after an employee of the saws owner didn't fix the e clip on correctly. The clutch grenaded and did the boss up super tight. I used pretty much all the force I could muster to shift it and ground it off in the end with a diamond burr after I couldn't shift it - it lasted a few months before letting loose. The stop I used was the Stihl one followed by rope when the damn thing didn't shift.
Got it back together again and hope it lasts now, all the parts looked good and measured OK but it is damn difficult to tell if components have micro cracks or a bit of stress damage. I know a few tricks in checking engine components and agreed with the owner that the repair bill was worth paying to see if it lasted - the other option was a complete rebuild with new components which didn't make sense.
 

Hey Spud, nice talk through [emoji106]
We used to use some sprays at work 15yrs or so ago, for highlighting cracks in metal components and the like. Dont quote me but i’m 99.9% sure they were made by “loctite” whether they still make it i’m not sure.
a clear “cleaner” spay in a white tin a bit like brake cleaner but stank like thinners,
a red tin with pink coloured spray “enhancer” that you just covered everything with,
then a “finder” spray, blue tin but clear spray and it reacted with the pink making it disappear but left blue traces wherever there was a crack.
Used them alot on ERF rear axles around spring saddles and diff casings, they had a spurt of shite metals being used to build axles and they were cracking up after 3-4 yrs of age. Poor!!!

[spudulike]

I did have a vague feeling it was yours, it was running like a bag O S and not revving, the coil sorted it whilst you were supping Prosek in Croatia I believe!

[spudulike]

3 minutes ago, Ratman said:

Hey Spud, nice talk through
We used to use some sprays at work 15yrs or so ago, for highlighting cracks in metal components and the like. Dont quote me but i’m 99.9% sure they were made by “loctite” whether they still make it i’m not sure.
a clear “cleaner” spay in a white tin a bit like brake cleaner but stank like thinners,
a red tin with pink coloured spray “enhancer” that you just covered everything with,
then a “finder” spray, blue tin but clear spray and it reacted with the pink making it disappear but left blue traces wherever there was a crack.
Used them alot on ERF rear axles around spring saddles and diff casings, they had a spurt of shite metals being used to build axles and they were cracking up after 3-4 yrs of age. Poor!!!

Interesting - Rolls Royce used harmonic resonance in their turbines, hit them and measured the resonance in the metal to see if the castings were good.

[Ratman]

Think i heard something mentioned about that on guy martins series on lancaster bomber

[Ratman]

What year did stihl start with the “auto retard coils” spud? And are they fitted to the smaller saws too?

[spudulike]

Not sure what year but there was definitely a shift from say the 064 to the 066. The older saws typically had dumb one setting coils but the later ones would roll the ignition timing advance to almost zero at start and then start advancing the timing dramatically from a few thousand rpm.

Get a strobe timer on the saw and shine it at the flywheel, that will tell you what's what!

[bmp01]

12 hours ago, spudulike said:

On the MS461, there is a strange alloy bracket that bolts across the crankcase mouth and goes right up in to the piston. There has been a lot of speculation on what it does but the clever money is on dome sort of diverter creating a strato effect on a relatively standard engine design. See pic below.

I believe that the piston probably had a very fine crack in it after I tried to remove the central boss from the clutch after an employee of the saws owner didn't fix the e clip on correctly. The clutch grenaded and did the boss up super tight. I used pretty much all the force I could muster to shift it and ground it off in the end with a diamond burr after I couldn't shift it - it lasted a few months before letting loose. The stop I used was the Stihl one followed by rope when the damn thing didn't shift.

Thanks for the explanation of that strato flange, much appreciated. Not seen anything like that before,  weird. Not something a manufacturer would add in unless there was some real benefit - performance or emissions. I wonder what happens if it's left out. ...

Regarding piston stops - if you had to reinvent the wheel for removing clutches you'd never choose to stop the crank turning by blocking the piston movement would you ? It's only because someone tried in the dim and distant past - while working on some ancient over engineered lump - that the procedure exists today. Time for a crank stop designed in on new engines...

Makes me cringe every time, imagining the forces going through pistons,  bearings etc.