Author Topic: Front sprocket removal (Read 10763 times)

callbr549 · « **on:** May 21, 2011, 01:00:12 PM »

I need to replace the front sprocket of my 1972 CB750. I can't get the 19mm nut to budge. I'm really worried about rounding off this nut -- an 18mm wrench definitely won't fit, but the 19mm is looser than it should be. When I start to put torque on it I can feel it starting to slip. Any advice about how to get this off? (I have bent the tabs on the washer back, so thats not a factor).

Rob

nashvegasmatt · « **Reply #1 on:** May 21, 2011, 01:03:54 PM »

Quote from: callbr549 on May 21, 2011, 01:00:12 PM

I need to replace the front sprocket of my 1972 CB750. I can't get the 19mm nut to budge. I'm really worried about rounding off this nut -- an 18mm wrench definitely won't fit, but the 19mm is looser than it should be. When I start to put torque on it I can feel it starting to slip. Any advice about how to get this off? (I have bent the tabs on the washer back, so thats not a factor).

Rob

wd/40 and some light heat usually does the trick. Also there is a jelly, that I can't seem to remember the name of that you may want to use. some type of penetrating jelly.

Toxic · « **Reply #2 on:** May 21, 2011, 03:33:05 PM »

You want to make sure those tabs are hammered perfectly flat. It doesn't take much to stop the nut from turning.

bollingball · « **Reply #3 on:** May 21, 2011, 03:52:52 PM »

PB blaster is better let it soak whack the head of the bolt to shock it impact driver would do it.

callbr549 · « **Reply #4 on:** May 23, 2011, 05:51:56 AM »

A couple of questions to clarify:
1. I don't have any experience heating things to get them loose. Do I use a torch for this? I'm nervous about residues that might be flammable -- PB Blaster, since I've been repeatedly applying that, and also any oil or other residue on the bike i might not notice.
2. When you recommend an impact driver you're talking about the kind you hold on a screw or nut and then whack with a hammer? When I try turning this nut with a wrench, the wrench doesn't seem to fit tight enough and it feels like it is going to round off the flats of the nut. If I put a socket on the nut and then hit it with an impact driver isn't that just going to round off all the corners at once?

MoMo · « **Reply #5 on:** May 23, 2011, 06:00:25 AM »

You need an air or electric impact, the hammering of the unit will break the corrosion free. If you do not have one, a local station might break it loose for a couple bucks, or free if they're into bikes...Larry

bollingball · « **Reply #6 on:** May 23, 2011, 06:06:00 AM »

Yes the hand held impact is the one to use. also is your socket a six point good quality? if not get one they tend to grab the flat part of the nut where a 12 point is closer to the corners. have you hit the nut or bolt with a hammer yet to shock it loose? Don't be timid hit it good and hard with the impact it will come off.
This is no time for a cheap Taiwan socket.

callbr549 · « **Reply #7 on:** May 23, 2011, 02:46:39 PM »

Socket I'm using is a six point Craftsman. I thought Craftsman were good quality tools when I bought the set, but now I get the impression that quality of diferent brands is one of those things that start fights with some people.

MoMo · « **Reply #8 on:** May 23, 2011, 04:26:30 PM »

Quote from: callbr549 on May 23, 2011, 02:46:39 PM

Socket I'm using is a six point Craftsman. I thought Craftsman were good quality tools when I bought the set, but now I get the impression that quality of diferent brands is one of those things that start fights with some people.

Well.....you could start an oil thread is you really wanted to see a fight. Larry

callbr549 · « **Reply #9 on:** May 24, 2011, 04:40:38 AM »

I'm confused about how this assembly goes together. I started this project because my chain broke and wrapped around the sprocket and got all jammed up. The sprocket was jammed at this point and wouldn't turn. I used the impact driver last night as recommended. When I did the chain came loose and the sprocket turned as did the nut I've been trying to loosen. I can't turn the nut with a wrench, but it does turn with an impact driver and the sprocket turns with it. I expected the nut to turn relative to the sprocket, but they only turn together. If I manage to get the sprocket to not turn, the nut won't turn. After a few hits with the impact driver the sprocket does seem to have some room to slide on the shaft that it didn't before, so maybe it is coming loose? I will appreciate any help you can offer to understand this. The parts fiche drawings don't make sense to me either.

bollingball · « **Reply #10 on:** May 24, 2011, 09:07:14 AM »

Keep at it as long as the shaft is not turning it will come off try a wedge of wood between front of sprocket and engine to hold sprocket I have a 750K8 with splines on shaft I don't know what yours has.

Brantley · « **Reply #11 on:** May 24, 2011, 02:18:31 PM »

You also might try wrapping enough of yr old chain around to grab both ends with some large vice grips. The two 10mm (or is it 9mm) headed bolts hold the sprocket to a mounting plate that is keyed differently than the sprocket. Try removing those first and sliding the sprocket back toward the engine to get more bite on the large nut (which also contains the chain oiler which is reverse threaded. Try turning that little flat screw out some.). PB Blaster is OK, but Kroil works better (how's that for tryin to start a fight?) Good luck.

bollingball · « **Reply #12 on:** May 24, 2011, 03:28:35 PM »

Kroil where's from that planet Kripton

Coyote13 · « **Reply #13 on:** May 24, 2011, 03:38:14 PM »

I'm retarded. Try PB Blaster and heat, then the Craftsman 6-point

Toxic · « **Reply #14 on:** May 24, 2011, 03:47:18 PM »

Jeez, nice tip on using the old chain to stop the sprocket from rotating.

That's a good one.

Bob Wessner · « **Reply #15 on:** May 24, 2011, 05:29:33 PM »

I'm a bit lost on this one, remind me, why is the sprocket turning, it's on a splined shaft?

bollingball · « **Reply #16 on:** May 24, 2011, 05:41:00 PM »

Is it in neutral or is the engine turning?

scottly · « **Reply #17 on:** May 24, 2011, 06:09:41 PM »

Quote from: callbr549 on May 24, 2011, 04:40:38 AM

I'm confused about how this assembly goes together. I started this project because my chain broke and wrapped around the sprocket and got all jammed up. The sprocket was jammed at this point and wouldn't turn. I used the impact driver last night as recommended. When I did the chain came loose and the sprocket turned as did the nut I've been trying to loosen.

The only reason to remove the nut is to allow the sprocket plate and sprocket to slide off the shaft past the nut and lock-washer. On my bike, a PO had broken the tabs off the washer and filed down any high spots to allow the sprocket to be removed.

hyde7278 · « **Reply #18 on:** May 24, 2011, 06:33:25 PM »

sound like its i neutral try putting it gear to keep it in gear and use an air or electric 1/2" impact gun, the speed of the impacts from the gun should be able to break the nut loose with out turning the shaft. the hand impact driver doesn't have enough impacts per minute to break it loose with out turning the shaft.

Brantley · « **Reply #19 on:** May 25, 2011, 10:43:10 AM »

Oh, yeah, forgot the whole put it in gear thing. 1st, preferably. If you already have another chain, you can mount that, turn yr rear brake adjuster way in and shove a small block of wood between the rear brake pedal and foot peg to keep the brake ON while turning the nut.

callbr549 · « **Reply #20 on:** May 29, 2011, 02:06:11 PM »

I've continued to soak with PB Blaster and hit it with the hand impact driver off and on for a week now, still no luck getting it to budge. I don't have access to an air impact wrench. This whole episode started with a chain breaking while riding it and it would be hard getting the bike to someone with that tool in this condition. I have some clarifying questions: 1. The impact driver I've got seems to be reversing directions, so after every hit I'm having to take it off and check to make sure it is turning the right direction. I bought it a local auto parts store, so probably not the greatest tool. Sears just opened a store here -- should I go buy a Craftsman impact driver? 2. I'm assuming this is a right hand thread, so I'm turning counterclockwise, correct? 3. I'm very nervous about using a torch to heat the thing up; I've cleaned the area, but there are still traces of grease, PB Blaster, etc and I don't want to start a fire. How clean should things be first? 4. If I do resort to heat, the part I'm trying to turn is inside the splined shaft, so I'm assuming I want to apply heat to the shaft, not the piece I'm trying to turn, right? I've attached a photo in case anyone can look at it and see something I'm obviously doing wrong.

Brantley · « **Reply #21 on:** May 29, 2011, 02:45:52 PM »

If yr worried about a torch grab a cheap heat gun. If you have a Harbor Freight in yr area they're normally around $10. Don't worry about a new impact driver, stop the sprocket and use yr 6 sided socket with a breaker bar. If you don't have a breaker bar you can make one by placing a long length of pipe (galvanized fence post works well, as does rusty old unusable fork tubes) over the handle of yr ratchet, thereby increasing the leverage and torque applied to the nut.

scottly · « **Reply #22 on:** May 29, 2011, 04:36:26 PM »

Just remove the tabs from the lock washer, and you should be able to slide the sprocket off.

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Author Topic: Front sprocket removal (Read 10763 times)

nashvegasmatt

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