Topic: 1975 Honda CB750F Clutch Lifter Plate Failure

[RodSOHC750]

I was assembling my clutch and turning the four bolts 1/2 turns in criss cross fashion.  Just as the bolts were starting to tighten down, a corner of the lifter plate cracked. What caused this?  I noticed the new springs are about 1/4 inch longer than the old springs.  What is the torque setting for the four bolts?

[Kawahonda]

They are Barnett springs, right?
Fresh springs are always longer than used springs.

[RodSOHC750]

You are correct.  Barnett clutch kit with kevlar friction discs and new springs. 

The paper with the kit says MT-15-4 (56 Lb Springs) and MT-10-4 (66 Lb Springs).

The spring package says 501-56-04015 Clutch Springs.   So I don't know what I have as far as spring pressure.

[unamusedd]

I used this DIY where he goes into depth about reinstalling that lifter plate and it worked for me. http://honda-cb750-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html I hope this helps!

[RodSOHC750]

I read this before installing the lifter plate.  I may have done something wrong to cause the plate to crack. It could have been during the disassembly. 

At the end of the instructions, it does not give the torque spec.  I can go off a tightening chart according to the bolt size. 

"Once the lifter plates seats fully (you'll feel it) tighten the bolts and you're done!"

[unamusedd]

I read this before installing the lifter plate.  I may have done something wrong to cause the plate to crack. It could have been during the disassembly. 

At the end of the instructions, it does not give the torque spec.  I can go off a tightening chart according to the bolt size. 

"Once the lifter plates seats fully (you'll feel it) tighten the bolts and you're done!"

If I remember correctly I tightened mine to 9ft lbs according to the hackaweek video Dino posted on youtube.

[RodSOHC750]

I just checked with Barnett company.  The springs I have are correct for the Honda model I have.  Their springs are generally 10-15% higher spring rate than stock.  The Barnett part number 501-56-04015 indicates 56 pounds spring rate at 1 inch. 

Looking at the design of the lifter plate, I don't think the spring rate should cause the failure.  My guess is the plate was binding during tightening, not tightened evenly, or not loosened evenly during the removal.  Or it could have been from age/wear.

[martin99]

The most likely cause of this IMO is that the spring was not seated correctly under the lifter plate. Looking at your picture of the underside there appears to be a small shiney witness mark where it looks like it could have caught on the 'step'. It's not uncommon for these to break in this way - even new ones. When you do it again, pay special attention to the position of the springs and do them up a quarter turn each time.

[Retro Rocket]

I'm surprised no one is making nice new billet lifter plates, I'd buy a couple...

[RodSOHC750]

I like your comment.  This component being made of steel could have justified the negligible weight gain.

[martin99]

I think Retro's talking about aluminium billet. I'm sure there would be a demand for them, wish I had the skills and machinery to knock out a few myself. Someone's missing a trick here I reckon (fancy having a go Frank?)

[Retro Rocket]

I think Retro's talking about aluminium billet. I'm sure there would be a demand for them, wish I had the skills and machinery to knock out a few myself. Someone's missing a trick here I reckon (fancy having a go Frank?)

Yes, aluminum billet, modern alloys are far superior to the old alloys Honda used, A nice billet aluminum piece would solve the problem, and i imagine it would sell well too...

[scottly]

The most common cause of broken lifter plates is miss-alignment of the splines on the pressure plate and clutch center. With the splines aligned, the lifter plate "bottoms out" against the posts on the pressure plate as the bolts are drawn up tight. When the splines are not aligned, the plate can't "bottom out" against the posts, even without the springs and plates in place, so the plate is bent down as the bolts are tightened, causing it to break.
 

[Jerry Rxman Griffin aka MuthaF'er]

The most likely cause of this IMO is that the spring was not seated correctly under the lifter plate. Looking at your picture of the underside there appears to be a small shiney witness mark where it looks like it could have caught on the 'step'. It's not uncommon for these to break in this way - even new ones. When you do it again, pay special attention to the position of the springs and do them up a quarter turn each time.

Hey Martin, can you paint everyone that's had this happen a more graphic picture of how the springs are supposed to be seated vs how they are NOT supposed to be seated?

[MCRider]

The most common cause of broken lifter plates is miss-alignment of the splines on the pressure plate and clutch center. With the splines aligned, the lifter plate "bottoms out" against the posts on the pressure plate as the bolts are drawn up tight. When the splines are not aligned, the plate can't "bottom out" against the posts, even without the springs and plates in place, so the plate is bent down as the bolts are tightened, causing it to break.

This is correct. There are 4 ways these 2 pieces can go together. Only 2 are correct. The splines MUST align or you will break the lifter plate every time. Trying to overpower the design by using a stronger lifter plate will not work if the splines are not aligned. You'll simply have a non-functioning clutch. We've had several discussions on this, though not recently. I'll try to find my pictures/thread that outlines the problem. To avoid it I always mark the top of a post and the lifter plate adjacent to that post with a black sharpie or such so it goes back together correctly.  You have a 50/50 chance of getting it right so many people are just lucky.

The stock lifter plate is completely sufficient if the splines are aligned. Are you sure yours were aligned?  Besides the pics above, there are good pics in that DIY thread about half way down.  In my thread I show how, if the splines are aligned you can be rather careless with tightening the bolts and still not break anything. The torque on the bolts should not be very high, 8lbs max. You'll feel them bottom out and stop turning very absolutely, when the splines are aligned. When they are not the bolts feel gushy right up to the point that the plate breaks, as the springs never seat.

[MCRider]

Here's the thread, similar to the one already posted. My post is down the first page a bit.  Good luck.

http://forums.sohc4.net/index.php/topic,98106.msg1092360.html#msg1092360

[70CB750]

Two more points:

- Check the fit without plates and springs, ends of those post sometime have little edge that makes them harder to fit in the groove.

- When tightening make sure the no spring is caught against the outer ring.

- Use screwdriver type of 10mm wrench to feel the torque better.


OK, 3 points 

[martin99]

The most likely cause of this IMO is that the spring was not seated correctly under the lifter plate. Looking at your picture of the underside there appears to be a small shiney witness mark where it looks like it could have caught on the 'step'. It's not uncommon for these to break in this way - even new ones. When you do it again, pay special attention to the position of the springs and do them up a quarter turn each time.

Hey Martin, can you paint everyone that's had this happen a more graphic picture of how the springs are supposed to be seated vs how they are NOT supposed to be seated?

Scottly and MCRider clearly explain the cause of the dreaded broken lifter plate whereas I clearly do not . Having had two break on me in the past I thought I had sussed out the reason, but obviously not. The forum puts the term 'expert' above my avatar, not me - actually 'old timer' would be a more accurate description . Anyways, I stand corrected and proof that you learn something every day

[RodSOHC750]

Success!   I installed a new lifter plate and it didn't break.  I used all the suggestions read on this post. Thanks everyone.
I first fitted the lifter plate minus the springs to be sure the fit was ok.
I lubed the lifter plate boss where it seats inside the inside hub.
I installed the clutch springs so the coil tips faced towards the clutch center.
I installed the lifter plate bolts with a couple of turns making sure the springs seated properly and wiggling the lifter plate.
I turned each bolt 1/4 turn in a criss-cross fashion using a nut driver and 10mm socket.  I could feel the resistance much better.
Every couple of full turns, I checked the springs, wiggled the lifter plate, and measured the plate height above the clutch housing using a caliper.  I adjusted bolts as necessary to maintain parallelism.
As the lifter plate drew down about 1/8 to 3/16 inch inside the clutch hub, I checked the lifter plate position at all four flanges using a caliper to ensure parallelism.  Checked springs also.
As I felt strong resistance to the bolts through the driver, I noticed all four bolts tightened at the same time which was good.  I verified the lifter plate was seated on the four posts.
I torqued the four bolts to 9-10 ft-lbs in a criss-cross fashion.