OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Rover Engines Rover Blade Boss Issue - snapped bolts

Hey Guys,
Got a small problem that has been bugging me for a while.
I have recently encountered quite a few Rover Mowers where the three small boss bolts have either already snapped or snap when I am trying to remove them to clean up the blade plate and replace the blades
To date I have been lucky enough to replace the damaged boss�s with spares however my collection of un-damaged boss�s is now low.
So my question is can I re-use these boss�s by repairing them or not?
I was thinking about drilling on the snapped part of the bolt on my bench press drill and then getting three fresh bolts that go all the way through the boss. I would then finish it off by adding a lock washer and nut or locknut for added safety.
I have tried going through previous threads but couldn�t find any suggestions.
As always I am happy to hear any suggestions. Time doesn�t worry me. Its more about fixing the mowers to make sure they are safe and good runners.

Hello Jaffa J and ODK members,

Well that's an interesting and significant question.
I wonder if this problem is due to a previous over-torquing?
I mean, more people nowadays using 'rattle guns'....
What's your opinion, given your experience and that it has been 'bugging' you.

There are legal issues in giving advice on critical components.
I will need to default to our engineer and Moderator Grumpy on this.
He will have an answer, I'm sure.

In the meantime (if it helps) Click HERE for some elevator music.

All very interesting.
------------------------------------
JACK

First, if you put Penetrene on those bolts for a couple of hours before you try to unscrew them, there's a good chance you'll get them out without damage. If you can tell by feel that they aren't going to unscrew, you grind off the bolt heads so you can remove the blade plate, then grip the projecting stump of the bolt with gas pliers. Second, if you put some Coppercote on those bolts before you install them, there's a good chance that in future you won't need to go through the Penetrene process.

However, once the disaster has happened, the next step is to recover the bosses if possible. It may or may not work out successfully, but you have a reasonable chance. Begin by soaking the threads in Penetrene for several days. Then, laboriously position a centerpunch impression exactly in the center of each of the broken off bolts. Once you have a small impression in the center, make it bigger with a bigger centerpunch and a bigger hammer. Then set it up accurately on the bench drill so the top surface of the boss is exactly square to the drill spindle, and the center of the centerpunch impression is exactly in line with the center of the drill bit. Clamp the boss to the drill table in a serious way. Choose a drill bit that is about two thirds of the nominal outside diameter of the broken-off bolt, but exactly the root diameter of a proper stud extractor. I'll explain what a stud extractor is in a moment. Drill all the way through the bolt and into the open air. Next, you use the stud extractor.

A stud extractor has a straight, parallel shaft with a few tiny straight longitudinal splines down the outside of it. You drive it into the longitudinal hole you have drilled in the broken bolt, then screw the broken piece of the bolt out by rotating the splined shaft. Here is an expensive example, which includes drill guides etc to help you get the drilled hole in the center of the bolt:
http://www.ebay.com.au/itm/Sealey-S...arts_Accessories&hash=item27d9f45b81

Here is an even more expensive example:
http://www.ebay.com.au/itm/BGS-Germ...arts_Accessories&hash=item1c199e27e6

The important thing is that you do not attempt to use a device called an ezy-out, which has a tapered left hand thread on its outside. These are cheap and readily available, but they only work on bolts that aren't very solidly stuck. The problem is that they screw into the hole you've drilled through the broken bolt, and then they hopefully just screw the bolt-stump out by continuing to turn them. Unfortunately when they meet resistance due to the broken bolt being stuck, they screw their tapered thread further into the center of the bolt. That expands the broken bolt, and makes it tighter.

Note that most of the tools you'll be offered when you search "stud remover" will be ezy-outs. Nearly all of the remainder will be clamping devices for unscrewing studs that haven't been broken.

Personally I've never been prepared to pay more than $100 for a device that helps to recover blade bosses that are probably worth less than $5 each. Yes, you resort to such expensive tools when you are dealing with car cylinder blocks, but not blade bosses. So, I drill the central hole, then try an ezy-out in a very tentative fashion, in the hope that the bolt wasn't really frozen in place. After that fails, I drill the hole out to the root diameter of the thread. Then, if the breakage happened some way down from the surface of the boss, I try to start a tap of the correct thread size and pitch, into the top of the thread, above the breakage, and proceed very tentatively. If I've done a good enough job with the Penetrene, the individual turns of thread will often be forced out of the old thread. I keep stopping and using a scriber to try to pick out more turns of thread. If the breakage happened right at the surface of the boss, I try to pick out a few turns of bolt-thread before I try to use the tap.

IMPORTANT: If you drill the "root diameter" hole even slightly too big or off-center, you'll have damaged the parent thread in the boss. Similarly, if you make a mess of running the tap into the thread after drilling it, you'll damage the parent thread. At that point, the blade boss is scrap. It isn't safe to rely on a damaged thread for a safety-related task. Similarly, you can't tap the hole oversize after damaging the original thread: there isn't enough metal around the original tapped hole, for the result to be safe to use.

Wow Thats a lot of info....But listen as it spot on!!!↑↑↑↑

Its really a common problem but simple to fix.

Remove the centre bolt. Heat the boss before you put a spanner to them....same for broken bolts. Heat and quench then remove. ALWAYS re-tap threads with a good tapping compound.

In a lot of cases if the heat quench process is done right you can pull some out with your fingers.

Easy outs...bleh! (Not worth the effot)or stud extractors and drill and tap are fine,but still need heat. (Note dont heat if you intend to drill and tap as the metal will be hardened by this process.

Helicoiling a std boss in my opinion wouldnt be cost effective,but can be done safely.

Start putting away sh ones when you see them,again ensuring you tap the threads correctly.

All in all its a common boss and easier to get another.

I just threw out 10 and various others.

I may have one or two left. There yours if I have them.

G'day Fella's,
I have been through the process of drilling those bolts out.
These days if there is just one to get out and its a short bolt (sometimes they are long) I will drill it out and re-tap it.

I normally buy a $10 mower just for the parts if I need a boss.

I have drilled all 3 out before and put through bolts, nuts, washers before also.

Another thing I have done: if the boss had short bolts snapped off, flip it over and tap threads into the other side of it.

If you have scrapped briggs engines laying around, the conrod bolts have the same thread and work perfectly.

My understanding of this arrangement is:
The centre bolt fixes the blade carrier to the out put shaft.
Turning effort from the engine is transferred to through the woodruff key to the boss.
The boss being attached to the blade carrier via our 3 small bolts, transfers torque to the blade carrier.
The 3 bolts also stop the boss riding up on the out put shaft.
Cheers from Mark

Guys,
Thanks very much for the specific advice. Grumpy you have given me a great suggestion. I do am a not a believer in purchasing an expensive tool for a task thats simply not going to bring enough benefit.

I will try the easy out as per your instructions. These example bosses had bolts that were already snapped before they came into my possession. To date I havent actually snapped any bolts as I tend to heat them up and remove them very slowly moving them back and forth until they come loose and break the rust seal.

Mark, I agree with your comments, its not worth spending any significant money as you can pick a scrap mower up for 5-10 and grab the boss off it with a little luck.

I will give it a try and let you know how it goes - I wont go down the re-tapping method as I can get replacement bosses fairly easily and I dont want to compromise the function of the boss in any way - purely from a safety perspective.

Sorry for the slow reply on this issue, been fixing many mowers over the last couple of months as the grass is going mad around Canberra!

Grumpy luckily I managed to pick up a few scrap engines so I have 3 spare bosses now for zero cost - so thats a plus.

I did however follow your instructions very carefully with the ezy out and the bolts really are stuck solid. I soaked them for quite a few days and no movement at all.

For now its no problem as I have a few spare rover boss's.

I appreciate the advice regarding not compromising the boss's structural integrity. That is specifically what I was after.
Peter

Peter, it's a pleasure to deal with someone who listens and thinks, especially when safety is involved. With many stuck bolt jobs, if all else fails it is always possible to just drill it out and tap the hole oversized, but not in the case of bosses, because the amount of metal around the original hole is often minimal to begin with.

Here's a tip for getting that centre mark right, if they are through holes or if the bolt is broken off below the surface. Grab a drill bit the exact diameter of the hole so that it self centres and lightly drill a small indent into the bolt then use small drill bits and work your way up to extractor tool size. If a bolt is snapped off but not seized sometimes using left hand twist drills in a reversible drill will get it to run itself back out as the drill cuts.

Another tip, one that I have used to do everything from free up a bolt to rejuvenate a rusted up pair of pliers. If you can find it, get yourself a tin of Wiltshire Flux Paste, used to be available from the plumbing section of most hardware stores. A small amount applied to something rusty and then heated gently with oxy torch will see the rust dissolve away.