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Hi All,
I have a Stihl BR 400 blower thats almost 30 years old but has been running well. Last week it fell off the back of my pickup, but ran well immediately after. Today when I went to start it, the cord pulls with little compression, and something inside freewheels until gravity stops it...I'm thinking the flywheel? Is it possible the keyway on the shaft has broken? I know this has happened to me in the past with lawnmowers but not sure about a blower. Can someone suggest a troubleshooting process to identify the problem?
Thanks in advance for any help.

For starters, remove the pull starter, and turn the starter cup back and forth, see if the fanwheel flywheel appears to move with it, just to get a better picture of things.

Thanks Fish,
Pull starter removed, flywheel can be turned by hand but some compression, and with plug out I can see the piston reaching the top of the cylinder as I turn the flywheel.

The flywheel is on the front, isn't it? I haven't ever worked on that model. I would say that the fanwheel is loose, and that may have something to do with starting hard. The weight of the fanwheel is factored into it all, and the flywheels are extra light.

Thx Fish,
Maybe I should have said starter cup instead of flywheel...it was the starter cup I was turning that seemed to have a little compression and caused the piston to move. Where /how do I check the fanwheel?
thx

Here is a pic. Is there a way to see the fanwheel through the intake screen?

Thx Bert and Fish,
Bert...not that mechanical...can you point me to the rocker cover?
Thx

I think removing the rocker cover is going to be very hard to do since there is not one.

Sorry for bad info folks.
t always throws me as most of my customers have 600's ( or bigger ) & I forget the 400 is a strait 2 stroke.
Incorrect post duely removed
Now going to stand in the silly corner with dunces hat on for 10 minutes.

On the diagram, part #16, the center part.
Can you look in there and see the fanwheel?
The fanwheel is #14.

Fish...
Took the fan housing apart and found the fan really loose inside....the keyway was indeed broken in two pieces. Thanks everyone...problem resolved, as long as I can find a replacement keyway

Replacement key installed without issue....no parts left over
EXCEPT....now the blower turns over fine, tries to fire once, but will not start?
Anyone any ideas? Didn't touch anything else except to take apart and re-assemble??
Thanks for any help

I am not familiar with that model. Did you have the flywheel nut loose?

Yes...in order to replace the woodruff key I had to take the fan and the flywheel off

So...the latest update is after leaving it overnight, I used a spark plug tester to check for spark....the blower fired up and ran, but would not respond to the throttle, and after about 10 secs began to smoke!! Immediately shut it off, but now wondering what could have caused this? Is it possible to put the flywheel on backwards? I don't think I did, but can't think of anything else?

Smoke from where?
The housing? Or out of the muffler?
It is possible that the flywheel nut was not re-tightened sufficiently, causing the flywheel to shift/move, thus changing the timing.

Thx Fish....yes, thats possible but I'm now thinking that when I wsa working on it it was horizontal so I'm wondering if some oil has seeped into the cylinder and thats the cause of the smoke? It appeared to be coming form the exhaust. I'll check the flywheel nut

Yeah, that will burn off. If it keeps up, your carb needle may be leaky. If it is still running, I would wait on checking the flywheel nut.
Check the air filter, it may need cleaned.

Thx....air filter clean, fuel flowing and spark....yet now it will not start at all??

Hi all,
After replacing the Woodruff key detailed above, the machine would not start. After two days of trying everything, I heard that familiar sound while pulling the cord....the key had broken again!!! Does anyone know what torque the flywheel nut requires, and is that maybe why the key broke a second time? I just tightened it without a torque wrench, and I'm thinking that didn't seat the key properly? Thoughts anyone?
Thanks

The key brole because the first time it happened it scored the shaft so the taper can not lock
he shaft will need any burr dressed off with a fine file then the flywheel & shaft lapped with some brasso .

trooper1954 said:

Hi all,
After replacing the Woodruff key detailed above, the machine would not start. After two days of trying everything, I heard that familiar sound while pulling the cord....the key had broken again!!! Does anyone know what torque the flywheel nut requires, and is that maybe why the key broke a second time? I just tightened it without a torque wrench, and I'm thinking that didn't seat the key properly? Thoughts anyone?
Thanks

Click to expand...

18.5 ft-lbs

Yes, the key only keeps the flywheel in place while you tighten the nut, the taper of the shaft is what holds it into place.

Here are the specs.

Thx guys,
Bertsmobile1, I looked carefully with a magnifying glass at both the shaft keyway,and the flywheel.... can't see any burrs or marks.
Waiting for the Woodruff keys....I ordered two this time!???

BTW, I've heard that 1/2" torque wrenches are notoriously "out" quite a bit when set under 50ft lbs....any thoughts?

Here is a bulletin

trooper1954 said:

BTW, I've heard that 1/2" torque wrenches are notoriously "out" quite a bit when set under 50ft lbs....any thoughts?

Click to expand...

The way to know for sure is to do a calibration test. I something that I do once a year as I have found a couple of mine off by several pounds.

trooper1954 said:

BTW, I've heard that 1/2" torque wrenches are notoriously "out" quite a bit when set under 50ft lbs....any thoughts?

Click to expand...

Depends upon the wrench and the way the owners uses or rather abuses it.
As a general rule you do not use a wrench in the lower or upper 10%.
Thus a 0 to 100 ftlbs wrench would only be used to torque between 10 & 90 ftlbs.
The closer to the middle the more accurate they will be.
The best are the deflecting beam and the worst are the micrometer adjustable wratchet types unless you paid a good 3 figure number for them.

I just Smurf 'em down tight!!

I use the AVE method. Tighten till you think it is right and say "click" or use the German method of Gutentight. Then you have the "Torque to wilbur" method. Tighten down till something gives and back off 1/4 turn.

Even a cheap clicker torque wrench is better than guessing. Even those $10 HFT are fairly accurate once they are tested and calibrated (if needed). So far I had only one to failed in 10 yrs.

Just what are you guys for left handed torques; again just guessing? I still working getting a LH 3/4 torque wrench but have both LH and RH versions in the 1/4, 3/8, and 1/2 versions. Just trying to decide if I want to get only 300 ft-lb or go to 600 ft-lb 3/4 RH clicker and convert the current 300 ft-lb clicker to LH since haven't seen LH to tighten beyond 300 ft-lbs.

Thx guys,
One more question....what's the best method to secure the starter cup in order to tighten the flywheel? Just another socket, or is there another method?
Thx

Personally I use a piston stop.

Ok...so the two new Woodruff keys are in at the store...pick up tomorrow. Here's the thing...my torque wrench only goes down to 20 ft lbs.....require 18.5 for the flywheel nut....20 okay or too much? Yes....I know they are set for a reason, but I'm just curious if an extra 1 1/2ft lbs would be harmful??
Thx

Hmmmm.....
So I got the new Woodruff key and installed it correctly oriented on the shaft. It was definately in place as the starter cup turned as I turned the shaft. It was torqued to 18.5 ft lbs as per specs, reassembled and pulled to start.....guess what?....first pull the key broke again!!!!!
The keyway on both the shaft and the flywheel are fine....inspected under a microscope for nicks or burrs...there are none. Anyone have any suggestions as to where I go from here???? (Other than the repair shop) ??

The taper on the flywheel is cactus
The key should never have any load on it
The tapers should lock tight
Press the flywheel on the shaft with your hand hard then while pressing try to turn the engine over .
If the flywheel slips on the shaft the tapers are not locking
The tapered end of the shaft must never get to the end of the hole in the flywheel because that allows the nut to bottom out and not load the taper to lock it .

How are you tightening it down? Locking the cylinder?
Did you look for light cracks in the flywheel? Look closely in the area around the center on both sides.
Here is the ipl pics for others to see.

Thx bertsmobile1 and fish,
I tightened the flywheel on by putting a socket on the starter cup but....at first I tried wrapping the starter cup with tape and using a pump pliers to hold it while tightening the flywheel with a torque wrench. Pump pliers would not hold, so put a socket on the starter cup but and then tightened. When I first placed the flywheel on the crank I tapped firmly with a rubber dead blow hammer to make sure it was firmly on the shaft before tightening.
At 30 years old I have a feeling that either the crank shaft or the flywheel are worn to the point they don't mate together firmly any more. I may bite the bullet and take it to a shop as am getting a little frustrated at this point....whatever the cost to repair it will be cheaper than buying a new one at $600!

Google "lapping a taper " it is not all that difficult to do
Use a fine compound like Brasso ( 4-8 micron ), should take about 1/2 hour.
Process is the same basically as lapping valve seats you just need a finner grinding medium
The blow with a dead blow hammer is not needed but if you do it should be a lead or hide one and not rubber.
You should be able to push a taper on with your fingers enough to hold good enough to do up the nut .

Hi Guys,
Don't really know where to start with this....Blower went into repair shop, and it was discovered that the flywheel needed replacing., that was why it kept breaking keys.That was done and a new woodruff key installed....$200!!!....and it took 5 weeks due to waiting on parts.
I took it home and put mix in it with stabilizer for the winter. pulled to start and guess what... woodruff key broke straight away!!!!
Does anyone have any idea what is causing this? It was difficult to make that first pull...almost as if something was seized.
Of course, as soon as I'm able it will be going back to the shop but I'm not confident it won't cost me another wack of $$.
Any help or advise appreciated.

Take it back, they own the problem.

They may have improperly tightened it down at the shop, and they should take care of it.

My thoughts exactly Fish,,,but we'll see if they agree!

Any idea as to what could be causing this continuing issue besides the flywheel/crankshaft/woodruff key problem?

Here is the generic bulletin on it.

Thanks Fish....but when you have a certified tech fixing the thing you'd assume he should know this, and I presume he followed the outline when he replaced the flywheel and woodruff key

Not if they are just a parts swapper.
The crank is probably damaged the same as what happens when a flywheel key shears .
And similarly it probably need to be lapped to the flywheel to repair the damage that is preventing the tapers locking together .

bertsmobile1.....you're right! Shop was not happy to see the blower returned this morning....told my wife that now probably needs a crankshaft and it's probably not worth it on such an old machine!! I wish we had techs that could fix things instead o being just parts replacers
Perhaps I should try and find a BR 400 for sale that I could use for parts, or does anyone think perhaps a machine shop could salvage the crank in some way? I know Stihl wants $250 for a new one!!
I'll review your much earlier post about lapping to see if I feel confident enough to give it a shot.
Any comments appreciated.

Was this a Stihl dealer?

trooper1954 said:

bertsmobile1.....you're right! Shop was not happy to see the blower returned this morning....told my wife that now probably needs a crankshaft and it's probably not worth it on such an old machine!! I wish we had techs that could fix things instead o being just parts replacers
Perhaps I should try and find a BR 400 for sale that I could use for parts, or does anyone think perhaps a machine shop could salvage the crank in some way? I know Stihl wants $250 for a new one!!
I'll review your much earlier post about lapping to see if I feel confident enough to give it a shot.
Any comments appreciated.

Click to expand...

The key is just there to locate the flywheel so the magnet is in the correct position with respect to the piston
Take the flywheel off and very carefully file the edged of the keyway, they do not need to be sharp just so long as the key is a tight fit
Now without the key apply liberal amounts of Brasso on the shaft and lap the flywheel by rotating it back & forth
Lift slightly every few seconds & regularly dab more Brasso on the shaft .
As the surfaces get closer to each other you will feel them starting to stick together .
Clean both surfaces vey well and do a test by pushing the flywheel on with your thumbs
IT should lock and be quite hard to pull apart when they two surfaces match.

Yes Fish....Stihl dealer. Thanks bertsmobile1....some good news is it's not neccessary. The shop came through for me and fixed it for free! They said the reason the blower was so hard to pull to start.....the pulling hard caused the key to break.....was that it was flooded and had a vapour lock. It was too late for me to take the plug out as the key had already broken on the first half-pull.
Just thought I'd follow up with the results, and thanks to both of you for the help.

Likely the guy that installed the new flywheel didn't torque the nut down enough, and it ran fine when he tested it and sheared when he shut it down.