Dolmar Kaboom!

[troutfisher]

Here's a PS400 a friend brought me, he said it quit right in the middle of a cut. Rod bearing let go.

 

[oldsaw]

Ouch, that smarts!!! Over-rev or defective component?

Mark

 

[PES+]

Dirt ingestion....either airfilter leaking.........run without filter or with course screen filter used in silt condtions.

It can also happen when enough fine saw dust gets through the filter and packs around the big end wicking away the lubrication oil though this usually only happens when running the winter screen filter in the summer

 

[441_Stihl]

ouch is right its not a good sight :bang:

 

[troutfisher]

When I removed the carb bolts they were barely finger tight. I think it got fresh air and over-revved. He said it was running goooooood!

 

[PES+]

See all the fine saw dust in the intake area? Also see the bottom of the piston...that is burned in saw dust.

It then sucked the dust in after the carb....the evidence is there....If the saw had over revved the big end hole and or the small end hole would be egg shaped

 

[THALL10326]

When I removed the carb bolts they were barely finger tight. I think it got fresh air and over-revved. He said it was running goooooood!

If you look closely at the ris pin in that saw its obvious what happen. She got to running to fast, overheated and kaboom. You say the carb was loose, theres where your high speed over reving came from. Sucking alittle air, running too fast and away she went.

To be fair there's not a brand name saw made thats hasn't had a bearing failure at some time or another. It happens. You case is fairly simple as to why.

 

[441_Stihl]

if its like a race engine they run the best right before they let go

 

[troutfisher]

I had a 365 husky do this, but that was my fault. I got a little screwdriver happy, looking for power. They go quick!

 

[PES+]

Can you post some pics of the piston out of the bore? a couple of angles will suffice

 

[PES+]

When you lean it out too much what happens is some molten aluminum will leave the piston and find it's way into the bearing and cause one or more bearing needles to seize and that causes domino effect to destruction.

 

[THALL10326]

I had a 365 husky do this, but that was my fault. I got a little screwdriver happy, looking for power. They go quick!

It doesn't take much of a turn to lean a saw out and fry it or dry it and loose a bearing. The ris pin in that pic is burnt bad showing your Dolmar was cooking some kind of good. Was she talking before she blew??

 

[troutfisher]

Can you post some pics of the piston out of the bore? a couple of angles will suffice

I can, but I've already sanded on it, cleaning it up. There was friction damage on the skirts, but the ring was still free and slipped right off. The top of the piston looked o.k.

 

[troutfisher]

It doesn't take much of a turn to lean a saw out and fry it or dry it and loose a bearing. The ris pin in that pic is burnt bad showing your Dolmar was cooking some kind of good. Was she talking before she blew??

O ya, I was pretty impressed with my tune-job, for a little while anyway!

 

[PES+]

Stihl has their students now blow engines in their gold school by deliberatly leaning them out till failure. Ask them how often they lose a bearing. I bet they are 6 or 7 pistons and cylinders to 1 crank for the melted aluminum I referenced. I have regularly run stock cranks at 50 to 1 oil ratio past 18,000 RPM on a regular baasis with no bearing failure. It depends on the crank structure and rod/bearing configuration. The amount of fine sawdust all over the saw shows that it was being forced hard for a length of time with a dull chain. It definately overheated from this treatment.

 

[THALL10326]

Stihl has their students now blow engines in their gold school by deliberatly leaning them out till failure. Ask them how often they lose a bearing. I bet they are 6 or 7 pistons and cylinders to 1 crank for the melted aluminum I referenced. I have regularly run stock cranks at 50 to 1 oil ratio past 18,000 RPM on a regular baasis with no bearing failure. It depends on the crank structure and rod/bearing configuration. The amount of fine sawdust all over the saw shows that it was being forced hard for a length of time with a dull chain. It definately overheated from this treatment.

Pest your correct. They did have us out there burning up saws by leaning them out. Your correct too that the bearings rarely failed. However a rule of thumb is two pistons and 2 jugs to every one crank and bearings. Reason being according to Sthil the crank flexes at full speed. If you keep tossing on new jugs and pistons you will in time blow the bottom bearings or lose a crank from all the stress and flexing it has gone through at above the normal rpm range it was designed to withstand. Good post Pest, see we can all get along.

 

[troutfisher]

How long do you guys hold a saw at WOT, when adjusting the high speed? How long does it take to cause damage?

 

[PES+]

Depending on what model they are using this would be good practice. I came from days when things like cranks were overbuilt by a much wider margin than many current production pieces. I know I sound like I am whining but I am simply offering my view formed from many years of working with all manner of engines and electronics.

I hate disposable tools and hate to see pretty much all manufacturers going this route in the name of units produced/sold.

I just try to take care of my again growing customer base and trying to talk to the factories themselves most times is laughable becasue they know everything and when there is a problem the problem never happened.

We're good....when I get a chance I will post a bunch of pics in a series and see who can deduce how the failures happened.

I contract out to companies specializing usually in failure analysis but some companies just don't want to know....not in the budget.

I am always available for troubleshooting and solving catastropic money wasting results of best laid plans.

As I stated numerous times I am not singling out Stihl nor anyone else.....

and no I NEVER get along with marketing people that is NOT in my agreements

 

[PES+]

There is no reason to hold a saw wide open out of the cut more than 30 to 45 seconds at a time when tuning. If the saw is stock it should take a full minute at a time held wide open out of the cut provided it is not too lean from the start.

 

[04ultra]

Depending on what model they are using this would be good practice. I came from days when things like cranks were overbuilt by a much wider margin than many current production pieces. I know I sound like I am whining but I am simply offering my view formed from many years of working with all manner of engines and electronics.

I hate disposable tools and hate to see pretty much all manufacturers going this route in the name of units produced/sold.

I just try to take care of my again growing customer base and trying to talk to the factories themselves most times is laughable becasue they know everything and when there is a problem the problem never happened.

We're good....when I get a chance I will post a bunch of pics in a series and see who can deduce how the failures happened.

I contract out to companies specializing usually in failure analysis but some companies just don't want to know....not in the budget.

I am always available for troubleshooting and solving catastropic money wasting results of best laid plans.

As I stated numerous times I am not singling out Stihl nor anyone else.....

and no I NEVER get along with marketing people that is NOT in my agreements

Pest Do everbody the favor and take the vacation... You really need it to relax ..Looks like the cold winter weather is having an affect on ya..




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