PDA

View Full Version : Got my stubborn blade bolt off... Now what?


leejp
05-22-2007, 01:35 AM
I've got a set of Meg-Mo's for my 36" walk behind. Hope these blades live up to the billing. I'm cutting once every 5 days and barely keeping up with the rapid grass growth.

This was the first blade change on the new mower, The bolts were stubborn. My impact wrench (cheap coleman) didn't budge them so I soaked in PB blaster overnight and used a 4' piece of pipe to get them off.

Now what? Once the Meg-Mos are installed, how should I tighten? I'm going to use some sort of anti-seize compound for sure. But which one?

Also... should I hand tighten or use my impact wrench which couldn't get the nut off in the first place. Some cursory searches here suggest that either would do but this is the first time with the Meg-Mos and I'm a bit nervous about slipping.

SSS 18734
05-22-2007, 03:39 AM
I tighten my blade bolts to around 80 foot-pounds of torque using a torque wrench. I can still easily take them off by hand, but I don't have to worry about the blades flying off either!

bohiaa
05-22-2007, 09:29 AM
I tighten my blade bolts to around 80 foot-pounds of torque using a torque wrench. I can still easily take them off by hand, but I don't have to worry about the blades flying off either!

GREAT advice..... also I allways put wheel bering grease on the threads of the bolts............ ALWAYS...........

MOW PRO LAWN SERVICE
05-22-2007, 09:44 AM
Versachem or permatex both are top.

MarcSmith
05-22-2007, 09:49 AM
if you apply grease or any other type of lubricant to your threads, then your torque values mean nothing.

I never applied grease or oil to any blade bolts....but when you are changing/sharpening the blades out a couple times a week its not an issue...

leejp
05-22-2007, 10:20 AM
if you apply grease or any other type of lubricant to your threads, then your torque values mean nothing.


???

Torque is the same regardless of the lubricity. Do you mean the likelihood that it'll back out?

MarcSmith
05-22-2007, 10:59 AM
???

Torque is the same regardless of the lubricity.

On the contrary....

From a strength and preload standpoint the ideal steel fastener would have a plain black finish, (sometimes called a light oil finish). This finish produces a fairly consistent K-value and does not compromise the strength of the fastener. This finish would be unacceptable on a bike since it corrodes easily. The common solution is to apply a zinc or cadmium plating to prevent corrosion, and apply a conversion coating such as chromate to keep the finish looking nice. If a more decorative finish is desired, the fastener is usually polished and chrome plated. Plating causes problems with high-alloy steels due to hydrogen embrittlement, if appropriate measures are not taken after plating to "bake out" the hydrogen. This is especially true of chrome plating which tends to lock in the hydrogen. Plating does not adversely effect the mild steel used for 8.8 fasteners. The torque-tension relationship is greatly affected by plating due to its effect on the friction coefficient. Cadmium plating reduces the friction by 25% and zinc plating increases the friction up to 40%. This requires a corresponding 25% reduction or 40% increase in required torque for the same tension. Stainless steel fasteners have a friction coefficient about two times the corresponding plain steel fastener. This does not mean that stainless fasteners require double the specified torque since they usually cannot achieve the strength of a steel fastener.

Thread lubrication is another variable that affects the torque-tension relationship. I performed experiments on approximately 20 lubricants and found that the lubricant can change the torque to achieve a given tension by a factor of two (up or down!) I found that super clean fasteners or those lubricated with light lubricants like WD-40tm require a high torque to achieve the desired tension. Fasteners lubricated with oil such as motor oil and the oil found on black fasteners require a medium torque. Fasteners lubricated with extreme pressure grease or anti-seize paste require the least torque. Interestingly, I found that Loc-tite has about the same lubrication action as light oil. I discussed this with the manufacturer and they said this was by design so that the torque-tension relationship would be approximately the same as plain steel fasteners with normal manufacturing oil.

Remember the bolt is essentially a spring. over stress it and it won't spring back... strip the threads and you'll need a torch...

leejp
05-22-2007, 06:05 PM
.
Remember the bolt is essentially a spring. over stress it and it won't spring back... strip the threads and you'll need a torch...

OK I see...

Since I'll remove the blades 1~2x/year I think I will put some permatax on the threads and tighten using the lowest setting on my impact wrench . Quite a few folks here have used this method with no problems.

Let-it-mow!
05-22-2007, 06:49 PM
I always thought you were supposed to add "running torque" to the specified torque value given for a fastener. Running torque is the torque it takes to turn the bolt before it bottoms out.

so if the spec is 50 ft-lbs, and a close-fitting grade 1 fastener takes 10 ft-lbs to just start it turning, you add the 10 and 50 to get a spec of 60 ft.-lbs.


If you lube a bolt and have almost no running torque, then you just stick with the spec'd value.

MarcSmith
05-23-2007, 07:57 AM
with the blades and other stuff this probably isn't much of an issue (lubing the bolts) But when it come to critical stuff, like car wheel, engine blocks, brakes ect...you never see them lubing bolts for the exact reason of over stress/under stress and not getting the required clamping force.

Ideally all nuts and bolts should spin and hand tight(no tools) usually results in 10-20 inch lbs of torque which is pretty insignificant in larger applications like mowers and such.

steve45
05-23-2007, 09:29 AM
I'd go with clean, dry threads. The best way to tighten a critical bolt (these are not critical) is to tighten the bolt until it's seated, then turn the bolt a certain number of degrees of rotation. What you're actually doing is stretching the bolt. By knowing the number of threads per inch, you can calculate the strain of the bolt.

Spark plugs are notoriously overtorqued. They often have a large hex, which many people interpret as meaning it needs to be extra tight. A spark plug shell is actually a tube, which is much weaker than a standard bolt. Improper torquing of a spark plug can actually change it's heat range.

Capemay Eagle
05-23-2007, 02:58 PM
I am curious about the MEG-MO blades. have you tried them yet??I would like to start mulching soon. I have a hard time with mulching because of my oaks. I need to bag my yard in the spring because of all the pollen and all the other junk that falls. I also have a holly that decides to drop it leaves in may:dizzy: . Useally by the middle of June I am ready to mulch. LMK how they work.

leejp
05-23-2007, 03:08 PM
I am curious about the MEG-MO blades. have you tried them yet??I would like to start mulching soon. I have a hard time with mulching because of my oaks. I need to bag my yard in the spring because of all the pollen and all the other junk that falls. I also have a holly that decides to drop it leaves in may:dizzy: . Useally by the middle of June I am ready to mulch. LMK how they work.

If you do a search here you'll notice a lot of posts on the Meg-Mos. They seem to work better on some mowers than others. Those folks who have mowers these work well in really seem to like them. Many folks swear by doubles (2 blades mounted on a x pattern which I don't think is possible with some mowers) as well.

Many folks here get religiously emotional about these blades (don't know why but equipment discussions are generally heated here). For a ~$100 total I thought I might try a set find out for myself as they have a money back guarantee.

extremerc76
05-23-2007, 11:59 PM
i saw that we have almost the same mower, not alot of redhawks out there! i have 32" belt (im cheap), but the deck is almost the same other than width. i know what you mean about getting the blades off the first time, i had the same problem. to put them back on i use a wrench on the bolt hex (the head under neath the deck) with a pipe on it wedged against my wall, then take my impact gun and nail it as tight as it will go. (i have a campbell hausfeld gun w/150lbs behind it). i still have both feet, so i guess it puts them on tight enough:laugh:
also when you put the blades back on make sure that the shims you took off are in the samew position and same amount of them when you put them back on!!

leejp
05-24-2007, 12:11 AM
also when you put the blades back on make sure that the shims you took off are in the samew position and same amount of them when you put them back on!!

You mean the spacers?

Actually... I was going to move one from the bottom to the top which raises the cut height a bit. Then I was going to move a spacer from the bottom of each caster to the top. This will only lower the cut height a tiny amount (caster spacers are taller than the blade spacers) but it'sll give the recommended 1/8~1/4" forward deck slope recommended. Right now my deck if flat.

Runzwiscizzers
05-24-2007, 12:26 PM
I invested in Mega-Mo blades last month. Have cut 3 times with them. Two cuts the grass was really tall from all the rain we had. Some areas I had to go over a few times to get the blades of grass to be a size to my satisfaction. I have noticed that they mounted a little lower on the deck, so I raised my cut 1/2" and will find the results this weekend. It was just cutting too close for my tastes.

Anyway, as for the quality of cut, I am pleased with them. I don't get the fine mulched cut that I expected (after viewing the video on their website). I mow with a 48" Scag Tiger Cub, 19hp Kawi. I am a homeowner and only put about 50 hours a year on my mower, they told me I should not have to sharpen these blades for a couple of years. We'll see.

One thing I don't like, is that when I engage the blades, the mower really sounds like it does not like it.

As for mulching, I don't know yet, I am not mowing these days with the chute cover on.

leejp
05-24-2007, 12:29 PM
One thing I don't like, is that when I engage the blades, the mower really sounds like it does not like it.

Do you engage at full throttle?

Turf Terror
05-24-2007, 12:34 PM
Versachem or permatex both are top.
I use Never-Seize and torque 10ft/lbs less.

MarcSmith
05-24-2007, 12:37 PM
One thing I don't like, is that when I engage the blades, the mower really sounds like it does not like it.


bring your throttle down some. the meg-mos have a lot more mass to get spinning so the clutch will slip a bit more until they get to the engine speed.

I'll bed if you mow some really thick stuff and the blades bog down, the engine may take a little longer to recover and get back up to speed as well.