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86 VFR750 - Changed Starter Clutch Now Bike Just Backfires and Won't Run


vfrMatt86

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I had the infamous crunchy starter issue. I took it all apart and found that that starter clutch was in multiple pieces.

 

I took pictures of everything, noting the orientation and re-assembled it all exactly as I took it apart. Now the bike turns over cleanly without any awful sounds but she just backfires and won't run. I'm assuming the timing on these bikes is fixed.

 

I've ordered new plugs and put the bike on a battery tender to top up the battery as she's been sitting for 3 weeks to potentially eliminate those as issues. Bike ran perfectly fine before I parked it 3 weeks ago to drop the oil and investigate the starter clutch.

 

Any one have any ideas or any threads I can start pulling to sort this? 

 

 

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Have a very close inspection of the Starter Clutch outer that the pulser bumps are all in good shape and not damaged.

Assume the clutch outer can only be fitted in one position? Make sure of this and that it is in the exact position of when it was removed.

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1 minute ago, vfrMatt86 said:

The starter clutch is brand new and the pulser bumper were not damaged. 

Well if thats all you've done then is there any chance the outer alignment is not correct? Could it be 180 deg out? Make sure all timing references line up.

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Hmm. I'll have to open it up again.

 

The only difference in the new part from the old part is that the original clutch had long pulser bumps and the replacement had smaller bumps and more of them.

 

ughhhhhhhhhhhhhhhhhhhhhhhhhhhh...... that's the problem isn't it. lol

 

 

 

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That is interesting.  Obviously the alignment on the splined shaft can only go in one position. If you didn't move the crank whilst apart that should be good.  The bumps could change the wave form or duration of the signal generated but that would seem to be more of an issue on computer controlled engines.  Is it possible to remove the guts from the new clutch and use them to rebuild the case with the long bumps? 

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No, it seem to be a sealed metal band around the clutch itself. I checked back on my order and while partzilla said it would fit it is a different part number.

 

The original starter clutch is part no: 28120-ML7-000

 

While the replacement I got was part no: 28120-ML7-690

 

At the time I thought it was an updated part. I see now that I was wrong. 

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49 minutes ago, vfrMatt86 said:

Hmm. I'll have to open it up again.

 

The only difference in the new part from the old part is that the original clutch had long pulser bumps and the replacement had smaller bumps and more of them.

 

ughhhhhhhhhhhhhhhhhhhhhhhhhhhh...... that's the problem isn't it. lol

 

 

 

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Mate, they don't look anything like each other, I'm sure this is your issue. Can't the original outer be used?

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I think perhaps a skilled welder could fabricate it to work. Sadly I am not such a man. 

 

I do have a 96 vfr 750 that will likely need this part at some point so it's not a complete loss. 

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3 minutes ago, vfrMatt86 said:

I think perhaps a skilled welder could fabricate it to work. Sadly I am not such a man. 

 

I do have a 96 vfr 750 that will likely need this part at some point so it's not a complete loss. 

At least you've found what the issue is. Good luck getting the correct one.

Cheers.:beer:

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Looks like a lovely starter clutch that isn't compatible with a 1986 VFR750F. 😂

 

The original starter clutch for the 1986 VFR 750 is 28120-ML7-000 and the 87 onward to the 96 used the 28120-ML7-690.  The video you provided being a representation of the latter. 

 

The website I bought my 28120-ML7-690 showed a picture for the 28120-ML7-000 and referenced that it'd be compatible. I assumed it was an updated part.

 

We were all wrong. haha 

 

 

 

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Had the same problem with my 84 VF1000F.  I had a good 85 starter clutch but the thing would rev to 2500 then bang and pop.  The lugs were longer so I ended up using the old outer and new inner with new springs etc. 

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10 hours ago, vfrMatt86 said:

Looks like a lovely starter clutch that isn't compatible with a 1986 VFR750F. 😂

 

The original starter clutch for the 1986 VFR 750 is 28120-ML7-000 and the 87 onward to the 96 used the 28120-ML7-690.  The video you provided being a representation of the latter. 

 

The website I bought my 28120-ML7-690 showed a picture for the 28120-ML7-000 and referenced that it'd be compatible. I assumed it was an updated part.

 

We were all wrong. haha 

 

 

 

 

The 86 VFR is analog, while the 87 and later become a digital ignition system.  They made A LOT of changes for 87, quite a few parts, hard and electrical, are not interchangeable.

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So.. in the event that I can't find one.

 

A couple solutions that come to mind for me are...

 

1. Buy a new (28120-ML7-690) starter clutch.. then figure out a way to separate the outer housing from the center hub. Perhaps the steel would expand faster thus allowing me to remove it?

 

2. Buy a 28120-ML7-690 starter clutch and grind down all the pulse trigger tabs. Then create a weld bead in the same position, height and length as the 28120-ML7-000

 

3. Weld the cracks in my broken 28120-ML7-000 starter clutch. Anyone know what kind of metal the cracked center hub is?

 

Has anyone had and solved this problem already?

 

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Please tell me if I'm wrong - the cracked portion appears to be a different metal than the outer portion with the ignition trigger bumps.  In other words, the cracks do not appear to extend in to the outer case with the bumps.    If that's the true, then could they be separated as you point out - is it maybe a press fit in to the outer portion?  It seems like the smaller piece between the cracks would be loose.  It's hard to tell what's holding that together.   If separating them could be solved then there might be an opportunity to swap parts.  Do you have a photo of the back opposite side of it? 

 

BTW - I'm going to take a stab at the welding question.  I think that would be very difficult to do with it in that situation as that's a pretty thick piece of metal to get a weld that would penetrate all the way through through the entire crack.  My guess is that at best a weld would be a temporary fix that would likely fail in a fairly short period of time. 

 

Welding a bead on the new clutch or maybe cutting the existing bumps off the old one and tacking them to the new one might work.  The machinist would have to be very precise in placement for a satisfactory result - but it seems plausible. 

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Yes. I've been describing it as a center hub and then a band with pulse trigger nubs or bumps but it's more of a casing I suppose. 

 

They are different metal. So they'll expand different with heat treatment. I'm assuming that the center was pressed in while the outer casing was heated. Swapping the outer casings is indeed one solution. Though I'm slightly concerned about fatiguing the metal if I heat it too much.

 

You can see in the one picture that the outer metal casing has been bent slightly due to the inner hub cracking. So I could possibly just pry it out and then carefully hammer it back into form.

 

 

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If you went around carefully and slowly started moving that bent over lip up in small increments, you could see if it wants to start to separate.  I do it on old Honda headlights and speedos.   Then I re-peen the edge back over very slowly.

 

It looks like the holes that the bolts go thru are rolled over as well to help locate the two together in the right clocked position.

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3 hours ago, Captain 80s said:

If you went around carefully and slowly started moving that bent over lip up in small increments, you could see if it wants to start to separate.  I do it on old Honda headlights and speedos.   Then I re-peen the edge back over very slowly.

 

It looks like the holes that the bolts go thru are rolled over as well to help locate the two together in the right clocked position.

A great point about being clocked correctly.  Presumably the newer unit has the same holes and alignment.   

 

It looks like the outer casing or whatever one might call it, was made in a stamping press from sheet stock while the cracked piece seems to show signs of being machined.  Are they both magnetic?  I would presume so.  On the left in the upper photo there are a couple of small holes on the side of the outer piece.  Is there any evidence of tabs or pins that may be holding the two together?

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