Is this gear toast?!!

[alexcagle]

Not a chainsaw, but:

I wish Stihl would strengthen, or redesign these BR550-600 cam gears.
I change about 5 or 6 of these a year, and I don't even work on that many Stihl's, except cutquik's.

Does anyone know what the main reason for plastic cam gear failure is?

Detonation?
Pre-ignition?
Decompression mechanism failure?
Heat?
Sticking valves/guides from carbon?
Excess valve rocker clearance?
Weak valve springs?
Lack of lubrication?
Slop in the gear pin hole?
Or just plain old fatigue, heat cycles on plastic making it hard and brittle.

 

[cus_deluxe]

My guess would be that it finally just had enough of feeling inadequate when compared to real backpack blowers, and decided to end it.

 

[cus_deluxe]

But seriously, im guessing the last on your list of possible failures is closest to the reality.

 

[fearofpavement]

To answer the original question, yes, it's toast.

 

[alexcagle]

My guess would be that it finally just had enough of feeling inadequate when compared to real backpack blowers, and decided to end it.

Is that a "Froidian Slip"...lol

 

[cus_deluxe]

Uhhh i dont think so

 

[alexcagle]

Now that I look at my pic, I see it's almost 14 years old......I'll stop complaining now.

 

[HarleyT]

Give some backround on all of these "failures"...

 

[cus_deluxe]

ive seen redmax ebz8000's run on 80:1 for 15 years, at least 500 hours and continue to run perfectly. These stihl 4 mix blowers rarely make it past a couple hundred hours, in my expreience anyway. We had 4 br600s at the golf course where i work, we now have one that BARELY runs, and 5 husky 580bt's.

 

[cus_deluxe]

None of those br600s had 200 hours. The 4mix works great for weedies but its just not a viable option for long term WOT operation in my opinion.

 

[alexcagle]

Give some backround on all of these "failures"...

Past two years:

Construction asphalt paving company is two of them.
Two were lawn companies commercial
Three concrete contractors
One landscape installation company
One Home owner
One parking lot striping company.
One Tree stump grinder.
-all cam gear failures.

 

[Andyshine77]

Just rebuilt a low hour br600 that had a bad crank bearing, which means it needed a new crank. Have another one that sounds like it has gravel in it when pulled over, haven't diagnosed it yet, probably just going to toss this one in the garbage.

IMHO these blowers are homeowner quality. They do make good power and are comfortable to use, I'll give them that.

Sent from my HTC One_M8 using Tapatalk

 

[mountainlake]

Stihl quality headed down hill bad, the only way to fix that is quit buying them. Polaris did the same thing with their snowmobiles, it took years but their market share went from over 70% to 20%. Steve

 

[HarleyT]

So what was going on when one of these failures happened? Was it being used as normal? Was it running full speed when it happened? Was the blower used as it should? Was any modifications done to the blower?
Did the gear just "crumble"???
What does Stihl say????

 

[HarleyT]

Had these failures occurred after someone worked on them?
Piston stop?
Not pointing fingers, just asking.....

 

[alexcagle]

Just rebuilt a low hour br600 that had a bad crank bearing, which means it needed a new crank. Have another one that sounds like it has gravel in it when pulled over, haven't diagnosed it yet, probably just going to toss this one in the garbage.

IMHO these blowers are homeowner quality. They do make good power and are comfortable to use, I'll give them that.

Sent from my HTC One_M8 using Tapatalk

Try @backhoelover
He has lots of parts for them.
*
Your gravely sounding one;
probably the cam gear.
That's what this one sounded like.
It's back running again now after smoothing down the sharp edges on the crank timing gear.

 

[earlthegoat2]

I've seen a fair number of these failures in both blowers and weed eaties. The cam system is definitely a weak point......among others.....

I've seen cam lobes wore down, pushrods bent, valves broken off at the base of the stem, gear jumps timing (also,related to cam gear failure). Things that are just plain improbable in an automobile or other 4 stroke small engine application seem to happen regularly with 4 mixes.

I've only seen one failure as explosive as yours but have seen plenty of cam gear failures involving simple missing teeth, jump timing, a crack, separation from the camshaft.

Since I had been battling 4 mixes for quite some time on the valve train end when I saw the first cam gear failure, I never stopped to ponder what caused them and just settled on the desperately simple explanation that they were just plain junk.

On one of the FS 4 mixers in which the cam gear teeth wore down to the point where the came would not turn anymore, the crank gear did have a sharp edge which I did conclude caused the problem. Many others did not have sharp edges though. Of the reasons you listed, I lean towards the last one. Fatigue and failure.

I have exactly 3 4 mix blowers (about 16 BR430s) and around 35 4 mix FS, FC, HL, etc series machines and the 4 mix blowers have way more problems percentage wise. They are on the way out for more 430s.

 

[ANewSawyer]

This is why only own one 4-mix and that one I paid less than half of retail for. I just don't see them lasting long term without major maintance. 2-stoke FTW!

 

[alexcagle]

Had these failures occurred after someone worked on them?
Piston stop?
Not pointing fingers, just asking.....

*
Piston stop? Not on those.
I use rope on those, and on the power stroke so the valves are shut.
How would that stress the cam gear?
*
I've also seen a few blowers with siezed wrist pin bushing/bearings that caused piston scoring and siezure.
*

 

[HarleyT]

OK, had anyone been into the engines that had this failure?