Chainsaw Spike Bar

[Mick Roseblade]

Could it be the bar is misaligned either because studs are shunted or the actual saw case has been pulled out of shape by the damage thus putting potentially straight studs out of alignment? I cant see how bent spikes would cause a bar to overheat so fast, but a misaligned bar would.

Edited July 28, 2021 by Mick Roseblade
added an extra thought

[Billhook]

Well he came back yesterday but had not had time to go to the local saw doctor, so I fished around in my mass of junk in the stores and found an identical set of spikes. 
Fitted them and attacked the nearest big log which was a twenty inch diameter bit of lime.  It cut through it straight and had nice big chips, but was reluctant to go easily and made relatively hard work compared to the 340 on the same log.  His bar was too hot for the back of my hand after one cut from cold whereas mine was only just warm on the 340

Anyway that rules out spikes as the main problem and so we are now looking for something that is not immediately obvious 

There is nothing visibly wrong with the studs and the cover slides on easily.

Nothing seems to be wrong with the sprocket though I need more advice on how to check that

So could the whole saw body be distorted somehow with no evidence of plastic cracking or other damage?

He seems to think that the 340 has always pulled a lot better even though it is 56cc and his is 64 cc. 
He uses my saw now and it cuts fine so it is not the operator 

As he says the 340 just wants to go to work whereas his does not.  ( a bit like me some days!)

So we have ruled out the bars and chains which are identical, bought at the same time, swapped them over and the 340 drives his bar and chain exactly the same as my bar

His oiler visibly is working with the bar off and makes a nice line with the bar on against a board.  We both use Stihl oil

As Holmes would say “ When you have ruled out all possibilities, then the conclusion, however improbable, has to be the answer”

Edited July 29, 2021 by Billhook

[Billhook]

The correct Sherlock Holmes quote!

“Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.” - Sherlock Homes”

[billpierce]

Run his bar for a bit longer (like a full tank) on some thick wood with your saw. Just to double check

[peatff]

1 hour ago, Billhook said:

The correct Sherlock Holmes quote!

“Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.” - Sherlock Homes”

 

Occam's razor

[sime42]

 
Occam's razor

A much underappreciated principal.

[bmp01]

Billhook, your latest report, says "it cut through it straight" so that's one tick in the box then ?

 

I like that you are eliminating the variables one by one. So doesn't matter which bar/ chain combo,  the problem saw is oiling but bar is still getting hot  (but we think the chain is ok and its throwing big chips).

So what about chain tension? If it gets hot through the cut tension will increase - that in itself will produce more friction, heat and reduce useful power to drive the chain. Whats the starting tension ?

 

Have you considered bar oil type? Is it the same between saws? Sorry if thats been covered already.

 

Watching with interest, pretty sure you'll get to bottom of it .

[bmp01]

The 391 is a plastic case saw ? I'll wager the case flexes a bit more with chain tension.

Can't see heat conduction being important (heat from bar into engine case on first run),  if anything the metal cases will send heat to the bar one the saw is properly hot...

[Rob D]

On 26/07/2021 at 07:01, Billhook said:

You may well be right Rob.  But we carefully checked the oiler both bar off and with chain running against a board showing a line of oil being thrown out in the conventional test.

And yes it did heat up quickly.

It did not seem to want to go into the log  in the same way as the 340 .  When it did cut, there were nice big chips coming off, but then it stopped cutting and heated up I suspect because he was trying to force it a bit into the log to make it cut which twisted the saw enough to cause the friction, the twist being caused by the bent teeth.

You would have thought that the log damage when it fell on the saw would be more apparent in either damage to the, sprocket, the cover or making the cover difficult to fit if the studs had been tweaked.

It is one thing at a time at the moment and he hopefully is coming back to work on Wednesday with a new spike fitted ready for the test.  At the moment the spike is the only visible damage but I agree that I could be distracted by my theory and have missed something more obvious.

 

Yep but if I may - where are the close up pics of the drive sprocket/bar/chain from both saws/bar+chain combos?

 

Getting those and checking them is the first point of call before you do anything else. Make sure everything is as it should be and is compatible.

 

I still think you are looking for an exotic problem that is really a simple problem. It'll likely be linked also to why his bar is getting hot.

 

It's the bar/chain/sprocket that is the things that do the cutting - nothing else - only these x3 items.

 

 

 

 

 

 

[Billhook]

Number one photo with the clean looking sprocket is his 391

Number two with the worn sprocket is my old 340

Then his oiler working followed by the obvious difference between the saws on the same bit of wood

His still produced quite big chips but is struggling with the same bit of sycamore 

I think his engine is poorly tuned which adds to the problems