Stihl MS150T chain brake problems

[Barneys mate]

Having hassle with the band brake coming off the clutch drum and fouling on one side off the chain (see pic.) when the brake it applied, both with engine running and stopped.

I've changed to clutch/brake cover housing as a complete assembly (you can still see the parts sticker in the photo), spur sprocket and needle roller bearing but the problem is still there.

Swapped a clutch/brake cover housing from a colleague's MS150 and the same thing happens on my saw.

Checked for play in the crank shaft but all tight.

Any suggestions/ideas gratefully received....

[bmp01]

 

As you've swapped plenty of parts and I'm assuming you swapped your mates clutch cover onto your saw (not clear) and that behaved the same then I'd guess the reassembly of the clutch cover onto the saw isn't going quite right. Is the clutch drum catching on the brake band at the top ? Brake band might now be distorted too. Is the clutch drum a genuine one and definitely the correct one? 

 

Might be better to post this in the chainsaw section. ....

 

Good luck with it. 

 

bmp01

[spudulike]

Worth checking the tightness of the engine mounts as I have seen plenty of in and out play on the clutch (not drum end float) that may cause such an issue and is a common issue on older saws. Just clamp the drum against the back of the clutch with finger and thumb then push the clutch in and out to see if the whole assembly moves in and out a bit.

An intermittent kill switch will be a sign of loose engine mount bolts.

[Barneys mate]

Thanks for that guys.  When my saw was run with my mate's clutch/brake cover, the brake band still slipped off (on my saw) but my cover (and brake band) worked fine on his saw.  Will check out the engine mount bolts, thanks Spud.

[bmp01]

1 hour ago, Barneys mate said:

Thanks for that guys.  When my saw was run with my mate's clutch/brake cover, the brake band still slipped off (on my saw) but my cover (and brake band) worked fine on his saw.  Will check out the engine mount bolts, thanks Spud.

That clarifies it nicely. Does sound like the clutch drum is in the wrong place relative to the brake band or the drum is wrong. Trouble is you'd expect the clutch drum to be wearing through the clutch cover... Worth swapping your mates clutch drum over to your saw ? (not a 2 minute job with outboard clutch).

 

 

 

 

[Barneys mate]

Thanks bmp01 and I was thinking along the same lines having checked that the mounting bolts were tight (should have mentioned earlier but all parts used are genuine Stihl).  While checking the end float of the crank as per Spuds suggestion (crank all tight) I noticed what seemed a lot of end float on the clutch drum itself.  After taking off the clutch assembly I noticed circular grove about 0.5mm deep on the inside face:

[Barneys mate]

I also measured the distance between the shoulder of the crank against which the clutch butted when tight and the inside of the clutch drum:  it turned out that there was a 0.75mm gap.

This, combined with the depth of groove, resulted in about 1.25mm of end float.

[Barneys mate]

To try and reduce this without pinching the drum against the clutch, I fashioned a "washer" out of a bit of 0.5mm steel sheet to sit between the clutch drum and the clutch assembly but over the crank shaft.  This would reduce the 0.75mm difference to 0.25mm and eliminate the grove.

[Barneys mate]

Having put it together, the clutch drum still spins freely on the crank  and most importantly the bad brake stays in place when applied but with the chain running and stationary.  A longer term solution would be a new clutch carrier without the groove!  Hope this is of some interest.

[bmp01]

Thats a result,  well done,  and thanks for posting the info and solution. 

My only concern is that the clutch drum has been moved a mere 1.00mm and i had imagined it needed something in the region of half the width of the brake band to fix it. But, you've been into it pretty thoroughly and tested it so i guess that's all it needed.  Nice one.  

 

bmp01