STIHL FS 91R has major engine failure / Also FS 91 common problems

Customer brought in a FS 91 that died on them while in use. I discover a major engine failure after an inspection and teardown. I also briefly discuss some common problems with these units.
#stihl #enginefailure #smallenginerepair

[@TheLawnmowerLady]

Nice autopsy! Good to see those failure points.

[@TGMForum]

Interesting, I've not seen one do this either. 😲 I'm amazed it didn't take a bite out of the cylinder or crankcase when it let go.. 💥

[@richhopp9869]

That's crazy. That engine looks like it has low hours on it. I've been rebuilding a bunch of these engines (HT 130 and HT 131) lately. Great video!

[@richhopp9869]

We can't get these style engines in California anymore.

[@Reiner_Markenfreund]

Thank you Wollys Workin, the damage pattern may have been the result. The piston is at the exhaust top dead centre and it had a mixture of approx. 1.14 to 1.16 due to a fuel problem and was therefore running in the range of the highest combustion, piston and slightly too low cylinder temperature. Piston too big, too hot. It could have burnt back into the crankcase with high overpressure under the piston. Ignited via the piston rings, which were far too hot. Thanks for the nice video. Another Stihl 4-Mix engine crankshaft with real shapely museum quality. MpG. EISENEXE Michael Fritjof Mueller

[@MHolt3573]

We had 5 backpack blowers that came in with engines locked up. All of them was due to wrist pin failure. I wonder why Stihl didn't put a wrist pin bearing on the 550-700 blowers. It make no sense at all.

[@Reiner_Markenfreund]

Hi speed user move force reaction.

[@wallysworkin823]

They did open up the wrist pin clearance a few years ago, It helped but still too many issues.

[@Reiner_Markenfreund]

@@wallysworkin823 Ok. STIHL US Get this isue here.

[@snoopfurlow1275]

I can fix it, adjust the valve lash,,i think sthil has went down hill

[@teamground0229]

Gulp, just bought a used 91r. It is a monster brush cutter. Guess all I can do is make sure I have the right mix and go forward. What is the clue that valves need adjusting?

[@innerman7096]

Yes I have a friend that experience that, he was using the Stihl fs131 and it just lock up and wouldn’t run ,when it was taken apart the piston was break flywheel pin damage and cylinder damage .its too costly to repair where I live and he didn’t had the machine for a year.that sucks because here we only gets a 3 months warranty

[@bullpup33]

I have a 91 and 131 r. Not a single issue. Allot these issues come from operator abuse. Bad gas, not letting the unit cool down, lack of maintenance, etc.

[@Evanx373]

​@@scottacher7408 I check the valves on mine if it starts running bad. Usually a quick adjustment fixes is. It's very easy to do and takes about 10-15 mins. I bought mine used though and I don't think the previous owner ever had the valves adjusted.

[@davidpavshak330]

When you refer to older models of the 91r with the common issues, what approximate year of these are you referring to? I’m not sure when they were first released. I have a 2019 model with a bit of vibration and tank vent issue I need to fix and came across this video. Cool and very informative video!

[@Gary_in_NoVA]

Great video - - thanks!!

[@kristiancastillo1730]

I just bought a 91 today should I be worried and return it before the problem arises?

[@evildrporkchop4628]

I have one at work that I use 6 hours a day without stopping every single day it'll be fine I'm sure some people just get unlucky

[@kristiancastillo1730]

@@evildrporkchop4628 appreciate it bro I love the weed eater it’s perfect for what I do on a daily basis compared to the 94.

[@evildrporkchop4628]

@@kristiancastillo1730 I gotchu brother

[@ToyotaTacoma-js6on]

Will Stihl pay for fixing it? And replace the engine?

[@wallysworkin823]

Most likely.

[@radone3922]

Just bought one and now thinking of returning after this video Did they warranty the unit?

[@wallysworkin823]

It was warranty. This was a rare occasion, it’s not a common occurrence.

[@eugeneoreilly9356]

When I see plastic gears,cams in an engine I say 'no thanks'.

[@Drillmechanic]

Piston rod bushing overheating may cause this piston damage I think

[@Johnnyfreitas1]

So no oil in these machines

[@andybecker2693]

I’m glad that Stihl bought the 4- mix design from Shindaiwa before Echo bought Shindaiwa or this crap could have been on Echo equipment. It has too many failure points and moving parts that outweigh the benefits.

[@twocyclesmoke]

Shindaiwa’s C4 design wasn’t bad when Shindaiwa was Made In Japan… Echo ruined Shindaiwa. Maruyama is Made In Japan. Most Stihl products are Assembled In USA, same with Shindaiwa who no longer promotes the “First to start last to quit” slogan.

[@eugeneoreilly9356]

Agree,wouldn't touch those four strokes.

[@shadetree134]

I have a fs91r bought it new in 2020. It is the biggest piece of junk I bought. Has not run right since I bought it. Seems like the high speed throttle is to low. in thick grass it will die. So this week I bought new carburetor and tool to adjust the valves. I bent the throttle rod the the carburetor it helped with the rpm . This has been garbage for what I paid for it

[@greenmarine5]

Looks like a combination of poor design and operator error. This is why one should read the owners manual and strictly stick the operation and fuel usage of the manual while under warranty. Following that simple guide line makes the company warranty valid no matter what. Having good employees that listen and care about their job helps as well....

[@wallysworkin823]

You’re asking for all three sides of the triangle lol. I agree with your statement but it never happens.

[@johnsmith7676]

That does NOT look like a robustly-designed, or -manufactured, piston. It definitely needs more "meat" around the pin bore.

[@182QKFTW]

All of that silicone is amazing. Looks like an amateur assembled it! And, probably did:/

[@leefagundes2566]

Switched to shindiawa stihl not reliable anymore

[@rodneyfalk4591]

Must be made in the United States factory if it was built in Germany, we wouldn’t have this problem because all the tremors and chainsaws that I’ve had that were made in Germany run and run really well just saying

[@johnsmith7676]

Tremors?

[@rodneyfalk4591]

@@johnsmith7676 weed eater. Lol

[@rodneyfalk4591]

@@johnsmith7676 weed eater. Lol