Stihl HT75 chain tension inconsistency

[Ekka]

You know, I've been around saws for long enough.

Have had this pole saw some 7 years now.

Have tried new bars, sprockets etc.

Have conversed with other HT75 owners both the old and new power head models.

I run 12 picco bar and chain same as ms200T, some run the micro but the same problem exists.

The chain goes really tight after a little use. You can slacken it off so the darn chain is hanging out of the bottom of the bar and start sawing, few minutes later it's tighter than a fishes assk no more!

I've loosend the bar nut off slighly and grabbed the bar and it can move a bit making huge amounts of difference to the tension. So I then tighten the living crap out of it not caring if I stripped the nut coz it's pissed me off for years now ... didn't strip the nut but guess what, the tension changed and the chain wouldn't turn.

Yeah, I've stripped it, cleaned it and even swore at it, all didn't help.

Now even the new ones do this crap. Seems between the bit of play in the sliding screw pin adjuster and the hole in the bar the crap thing just moves or something.

So, anyone conquered this BS?

 

[BostonBull]

You know, I've been around saws for long enough.

Have had this pole saw some 7 years now.

Have tried new bars, sprockets etc.

Have conversed with other HT75 owners both the old and new power head models.

I run 12 picco bar and chain same as ms200T, some run the micro but the same problem exists.

The chain goes really tight after a little use. You can slacken it off so the darn chain is hanging out of the bottom of the bar and start sawing, few minutes later it's tighter than a fishes assk no more!

I've loosend the bar nut off slighly and grabbed the bar and it can move a bit making huge amounts of difference to the tension. So I then tighten the living crap out of it not caring if I stripped the nut coz it's pissed me off for years now ... didn't strip the nut but guess what, the tension changed and the chain wouldn't turn.

Yeah, I've stripped it, cleaned it and even swore at it, all didn't help.

Now even the new ones do this crap. Seems between the bit of play in the sliding screw pin adjuster and the hole in the bar the crap thing just moves or something.

So, anyone conquered this BS?

Havent come across this problem yet. Have you tried changing the chain adjuster out for a new one?

 

[rreidnauer]

Have you tried changing the chain adjuster out for a new one?

Or, remove the adjuster altogether.

There's only two reasons I can envision a chain tightening with use.

1. The bar is expanding from heat, at a rate higher than the chain. (unlikely, but a consideration)

2. The adjuster is "adjusting" on it's own from the saws vibration. (also seems unlikely, but it seems to be the only other possibility)

Remove the adjuster if possible, and report your findings.

 

[rxe]

I've got two of them, one about 5 years old and the other 1 year old. I've never noticed a problem with tension.

If you think about it, your bar has to be moving relative to the sprocket - the adjuster only holds it in the right place while you tighten the nut. When the saw is working, I doubt the adjuster makes a difference.

Are they the original bars? If they are replacements and the new ones are thinner, then maybe they are moving. Is anything blocking the clamping force as you tighten the nut?

 

[straight6jeff]

sounds like

This used to happen on a KE 125 motorcycle I used to have. On the saw, when the chain tightens, are the bar nuts tight? I'm thinking the bolts might be stretched. Give this a shot if you have not already. Tighten the chain normally. Tighten the bar nuts, then back off the adjuster so it is "nuetral floating". If you can, take a torque reading on the bar nuts. When the chain tightens up, see if the adjuster is still neutral, and take a torque reading on the bar nuts. See what parameter is changing. Also, could it be that the heat generated in the motor is causing the entire case to expand?

On my bike, it was a tweaked swingarm that was causing my problems.

 

[Ed*L]

I've had my ht75 since they first came out. Never had the problems you describe.
It sounds like the bar isn't getting enough oil. But thats just a WAG.
I have found that the saw head works best when it's clean. Due to the nature of the tool, crap likes to build up big time inside the cover. Tearing it apart and cleaning are a daily requirement on that saw.

Ed

 

[belgian]

I have seen this phenomena happen only with worn out sprockets, when the chain runs in and out the formed "trail". Since your sprocket is new, this is very unlikely, but give it a close look (bearing, roundness). Also check is the chain is compatible with the sprocket used.

There cannot be many causes to it...

 

[Ekka]

Well I had a little time today before the job started.

So, pulled it all apart.

Got a straight edge and found the cast alloy surface wasn't flat and neither was the plastic cover.

Pulled out the flat file and filed both flat as a tack, the drive sprocket is new, bar clean everything hunky dory.

Fixed it, ran well.

So what happened was when you tightened up it was only clamping the bar a little bit right where the nut was, then it could move a little, but now it aint moving, I tested it with a 2lb hammer. :hmm3grin2orange:

 

[Ed*L]

Glad you figured it out!
Just for grins I'm going to check mine tonight, see just how flat it is.

Ed

 

[Ekka]

Well, just some feedback.

Hasn't missed a beat since, that's what it was, the clamping faces not flat.

 

[Lakeside53]

, but now it aint moving, I tested it with a 2lb hammer. :hmm3grin2orange:

you can still get non-metric hammers down there?????

 

[Ekka]

It's the plumbing and thread world that's a real mess!

 

[Lakeside53]

NO kidding... My dad just came up for NZ with a plumbing part for me to match.. What PITA.. looks like a British steam pipe thread on one end and someother wacky thread on the other... Might be easier for me to make an adapter on my lathe.

Screw it.. I'll show him how to use JB weld to stick the wrong thing to the right thing.

 

[Lou]

NO kidding... My dad just came up for NZ with a plumbing part for me to match.. What PITA.. looks like a British steam pipe thread on one end and someother wacky thread on the other... Might be easier for me to make an adapter on my lathe.

Screw it.. I'll show him how to use JB weld to stick the wrong thing to the right thing.

If your Dad like mine was you will pay the rest of his life for doing something half-fast. If I had the lathe and the talent I'd use it as a showcase for what I can do. That would cause my Dad to puff out his chest instead of raise a lump on my noggin.

Why is there never time to do it correctly once but time to redo it 3 or 4 times?