OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Getting Blade boss Off

Hi All, Well, flushed with success from the repair of a trimmer (helped here a lot), I foolishly bought an old mower from the tip for a repair project. It is a Victa with a 3.5 HP briggs and stratton classic model: 9D902 Type: 2091 B1 and Code: 05110351. I suspect it has serious engine damage as there was no compression and a lot of metal shavings around the carby (did'nt see that until I got home!). Anyway, I have started to pull it apart. The piston and valves move up and down and I can't see any scoring on the cylinder wall. I am stumped at the blade boss. I think it is a tapered shaft as I can see a pin in it but a search on these forums does'nt say which way it should be knocked off (up-towards the top of the mower or down). Does anyone know how I should go about it. The blade holder bolted into the end of the boss. Here are some photo's:





As always I am grateful for help....

I tried a puller and that didn't seem to go very easily. I did not want hit it too hard in case of colateral damage to some other part. I've got a heat gun, I might give that a go. I am assuming it will come off downwards i.e. towards the ground.

I have had succsess with using a propane torch and heating it up till its very how (not too hot to melt he oil seal though. then hanging it upside down with a bolt of the same thread as the blade plate but longer wound in a fair way and solidly hitting it with a hammer.

Maybe this is another thing I should make a youtube video about.

Thanks. I only have a heat gun. It is a double keyway. God knows why things are so difficult. I'll have another go in the morning.

If you have a puller, you could try applying a fairly large axial force then smacking the hexagonal end of the puller screw axially with a large hammer. Before you do that though, put a piece of metal in between the threaded hole in the end of the crankshaft, and the conical tip of the puller screw. That will protect the thread.

If it is well stuck, I agree with Joe - heating it up while applying the puller and smacking the puller screw is likely to help a lot.

All this is based on the assumption that there is no retaining pin. I'm not familiar with the model of engine you have, so I make no promises about that.

Hi Grumpy,
Yes I am back again!. Here is another photo. There is a slotted bolt (?)that has an internal thread to hold the blade holder bolt. I am thinking this has to be removed first. Or not?

I'm not sure how this relates to the blade plate, but you seem to have photographed a nut that is retained by an ordinary split-pin (which Americans call a cotter pin, thus confusing everyone else since we use that name for something quite different). One end of the split pin will be a head: the pin consists of a half-round piece of wire bent back on itself, and where it bends a head is formed. To remove the pin, grab the head with a pair of pliers and pull it straight in line with the axis of the pin. Once the pin is removed you can undo the retaining nut that the split pin is locking.

I'm currently confused because the previous photo seemed to show the end of a crankshaft with a sprag clutch hub on it, indicating it is part of the pull starter mechanism. The blade plate is at the opposite end of the crankshaft from the starter. Furthermore the retaining screw seemed to have been removed from the end of the crankshaft in the previous photo. Now we see a part that seems to be a different shape and has a retaining nut and pin.

Hi Grumpy,

Sorry, mate but my photography isn't up to scratch. I'll get some more. The "split pin" is the end of a wrench which confusingly got in the photo. The end you're looking at (in the photo above) is the bit that holds the bolt for the blade holder. The slotted section is where the blade holder bolt goes. It threads down into it. I think it is just a very stubborn item that has to be pulled from the shaft somehow but I am not sure if there is some trick. Tomorrow I'll take it to my lawnmower repair shop and he'll help me out since that's where I'll buy the parts. I have taken a better shot now that shows the offending item. here it is:


You can't see them in the photo but there are 2 slotways on the shaft. I have given it a good belting with the puller and used my heat gun but it won't budge.

That picture is clear, and I don't see anything in it that keeps you from pulling the blade boss off with a puller by smacking the end of the puller screw. However if it is really stuck, a propane or oxy torch on the body of the blade boss (definitely not on the crankshaft) should do the trick. Unless it comes off fairly quickly though, heat will be conducted to the crankshaft and will destroy the oil seal, which you would then have to replace. Incidentally you were correct in calling the longitudinal slots in the crankshaft and blade boss keyways. It is a bit unusual to use two of them; perhaps they had a problem with keys shearing in some application and that was their response.
A heat gun does not supply enough heat to be any use for this job, probably by a factor of ten. It also applies the heat over a wide area rather than right where you want it, and this would be a bad idea.

blade bosses are notoriously bad to get off. if it were a standard boss ide say cut a slit all the way through it with and angle grinder and open the boss up with a cold chisel but because it looks like a rare and expensive boss i wouldn't recommend it unless you can get one cheep or secoundhand

the raised part of the boss that has the slits through it isn't the actual crankshaft is it? if you look closely its a machined step that the blade plate sits in. if that is the case then when you try and pull against it then obviously its not going to do a thing. im not 100% sure thats the case in your instance but thats how the older victa bosses use to be along with most bar blade ones. as joe said you can put a blot in there and pull against it but make sure its a long one and that it is all the way in so you dont strip the threads because its possible with the amount of force applied by a puller. if you use this trick then drill a small hole in the bolt for the point of the puller to press against.
hope this helps!
regards jay

Thanks mowernut. You're right about the puller not working and the reason, as you state, is that the point where the puller mounts is part of the Boss and not the crankshaft. It's just pulling against itself.....all that time...sigh..I will think about the bolt trick.

Jay's solution requires that the axial hole in the blade boss has a blind end and an internal keyway. That would be rather difficult to manufacture, and therefore expensive. Weird that they would do it that way, which makes me suspect they didn't. The screw-slots in the end must also have a purpose: they cost money to make, so they were made for a reason.

Have you tried treating the end part as a screwed-in retainer for the blade boss? It may unscrew from a thread in the end of the crankshaft, leaving a crankshaft-sized hole in the blade boss, which would make the blade boss easy to manufacture. The retainer would then have a double purpose: it would have a male thread sticking out from the far side, to engage the internal crankshaft thread, and a female thread in the front, to receive the blade plate retaining bolt. If it works that way, all you need to do is unscrew the retainer, using the screwdriver slot in the end of it and holding the body of the blade boss to keep the crankshaft from rotating. You will need to make a special screwdriver tool to do it, if it works that way.

Thanks Grumpy. I am pleased to report that it is off! I tried the bolt trick but wasn't getting anywhere. I decided to consult the local mower man and he had it off in 5 minutes! (I have promised to buy the rings and stuff from him). Guess what - he used the bolt trick. First He sprayed some oil on it and then belted the boss with a ball pein hammer all around its shaft. Then he did exactly the same as I was doing (per mowernut). He threaded a bolt down the shaft of the boss where it engaged with a thread on the crankcase. He then got an ENORMOUS PULLER (it made mine look like a toy) and attached it to the bolt and the underside of the boss. He did'nt even use a hammer on the puller just a spanner. A few turns of the puller and the bloody thing came off......Now onto the next episode...........

Glad you got it off with no damage. Mowernut, well done - you got there quickly, and with no destructive side-trips.

I'd still like to know what the purpose of the screwdriver slots is, and why on earth they would make a device that is bored to a blind end, and then has a keyway hobbed down to the blind end,for no apparent reason. However, that part of it isn't a Briggs part, it was some unknown mower firm.

Small pullers are for small jobs. I have a little puller, but I only use it where there isn't room for a big one. The whole idea of a puller is to apply massive rigidity and massive forces; big strong ones usually do less damage to the parts than little feeble ones. Of course you also need to have both two and three jawed hubs to be able to do a normal range of jobs.

good to see you got it off

Well here is the bad news. I bought the mower for $25 thinking it would make a nice repair job/hobby. I have now inspected the cylinder bore and it is really scuffed up at the bottom and the rings are completely worn. The cost of a re bore is $100, the cost of new rings and piston about $160. New seals and gaskets - never got that far. A brand spanking new engine would cost less and a complete new mower you could probably get for a little more. I guess they're just not meant to be fixed up anymore....sniff..

Good news is you can easily get $25 for the magneto and $20 for the carby on ebay, if you are in a major center you should be able to sell the base as a whole as well

Good thinking Joe. While I was in the depths of depression ($25!@#%!!) I spied a lawnmower upside down on a neighbours pile of rubbish. They gave it to me, probably felt sorry for me ($25!!). It is now the object of restoration. It is a "Flymo" with a 50mx Briggs and Stratton. They said it seized up after the floods (Mackay 2008). But it still turns and there is compression. I'll post a photo tomorrow under a new thread. Stay tuned for the adventures of sparker!

i wreck out mowers that are only good for spares, in parts sometimes if ur lucky you can make more than if you sold it whole!