Sunday, December 21, 2008

The Venerable 4 Speed Clutch - Part 2

Before too much time slips away, I had better post my follow-up to The Venerable 4 Speed Clutch - Part 1 In that post I told of many of the most common problems with this clutch design which Harley used from 1941 until 1984. As promised, I would like to now give a few tips on making it work even better than when it was new. Some of these are aimed primarily at drag racing, but many are readily adaptable to street use.

  1. Starting at the back of the assembly, a 5 stud clutch hub is a worthwhile upgrade for performance use. Whether you upgrade your existing hub, or buy a new one may come down to a money issue. If you can change the studs yourself it may be cheaper to do that, but if you have to pay someone to change the studs, it may be just as cost effective to buy a new 5 stud unit.

  2. Replace the "clutch hub fiber disc" with the "Nylatron" unit. In normal use, this fiber disc works as another clutch plate. That means that it is susceptible to making the clutch drag if there is insufficient release between it and the back of the clutch basket. Since this plate is behind the clutch hub bearing, it is also inordinately susceptible to grease from that bearing, further enhancing the probability it will drag. Whether the Nylatron disc was designed this way or not, what I like to do is treat it like a bearing rather than a clutch plate. I grease up the Nylatron disc on both sides to make it unlikely to give any drag. An added bonus to the Nylatron is that it is "full floating", so you don't have to worry about riveting it in like the stock disc.


  3. Next, in place of the stock clutch hub bearing retainer, install a "Ram Jett Retainer". I believe this little item is named after its originator, but is now being sold generically by all the major parts wholesalers. This little item is a rigid plastic/nylon disc that goes on after the basket is installed on the hub. It is installed with snap rings in place of the stock "spring clips". Depending on the indexing of the disc, it will give more or less end play to the clutch basket. Remember what I said about the Nylatron disc being used to make the assembly like a bearing rather than another clutch plate? The Ram Jett Retainer forms the other end of this "bearing assembly" and controls the end play. Controlling the end play eliminates the basket from "walking out" and causing clutch drag


  4. Clutch plates. Besides making sure that the plates are in good shape (not oil soaked or glazed) the other consideration is what use the clutch will be put to. For even hard street use, I would still recommend cheap replacement fiber discs. I remember (from back in the old days) one particularly successful street class racer used a particular brand of cheap aftermarket fibers with great success. Due to having a high horsepower motor along with a street tire, he slipped his clutch while launching the bike, managing a near perfect blend of RPM and traction. Sort of like a slipper clutch, only with the rider's clutch hand providing the magic. After every pass, he would swap the clutch plates out, allowing the most recently run ones to cool. I wish I could remember what brand plates he said he ran, because he did say not all of them worked equally well.

  5. Working our way out, an aluminum pressure plate will almost always work better than the original stamped steel one. They don't flex. They are also surprisingly affordable.


  6. The -41 clutch springs will give more pressure than the later hand clutch versions. Keep in mind that this will make your lever pull a little heavier though (that is why they changed them when they eliminated the mousetrap; also known as a hand clutch booster)


  7. The clutch spring retainer is the steel disc at the outer end of the clutch that the 5 nuts (now that you upgraded from a 3 stud hub) tighten. It will have 5 "nubs" that the special nuts index on. You're going to want to grind those nubs off. Discard the special nuts and use nylock nuts in their place. Now you will be able to get a fine adjustment on the pressure plate rather than in 1/2 turn increments as the special nuts provide.
  8. Now if your bike is going to be used mostly on the street, and you have no clutch drag, you are all done. If, however, this clutch is going to see some major drag racing use, you might want to keep reading. Most clutch problems on the drag strip are related to dragging, not slipping. Even a clutch with perfect street manners will tend to drag when your bike is staged and at 4000 RPM or more. Remember, all the clutch needs to do is "pull" your bike an inch or two and you have red lighted. Besides, it is pretty much impossible to cut a good light when distracted by a dragging clutch. The solution (if you have addressed all of the items here and in the first post) is to add more release travel. As I mentioned in part 1, you can remove the hand grip to allow the clutch lever to move farther. A layer of electrical tape will make the bar a little less slippery without a grip. One last trick. You can also add a little more travel to the clutch release by shortening the release arm (the lever that comes off the top of the kicker cover). You should be able to take about an inch out of the center of this arm without adding too much misalignment to the cable. Remember, this will also make for a heavier lever pull.

There you have it! All the tricks and tips that I know for the 4 speed clutch... well, at least all of them I remember. Will this solve all of your clutch problems on the street? I think so. On the strip? To a point. Even with a more modern clutch, I found that a 6000+ RPM launch required a line lock on the front brake to avoid being pulled through the lights. But for a 60 year old clutch design, I think you'd have to agree it was a good one.

10 comments:

Anonymous said...

Excellent read Lee,I need to do some clutch work now!
I've often considered pitching the stamped steel pressure plate....

jbfrmca said...

i think the ram-jett is only used on three finger clutchs only. if you look at the letters there are only three and if you try to line them up on a five finger a couple of them will be tight and other's will be loose. i have'nt seen one made for a five finger. that's why i use a clutch tamer.

St.Lee said...

Good Point jbfrmca, (jb for short?) You can however usually find two holes that match up with the 5 stud, and then with a appropriate shim behind the retaining ring on a 3rd stud, it will work. I just did one like that last week on one of my Knuckles. A guy could also machine the recesses deeper as needed if you have the equipment.

Jack Hester said...

Where can the Nylatron clutch hub disc replacement be found? I have an OEM set of replacement discs to rivet to my existing clutch plates. Plus the clutch hub. But, wouldn't mind trying the Nylatron disc, as well.

Jack

St.Lee said...

Jack, Custom Chrome carries them under part number 18327 with a suggested retail of $13.99

Jack Hester said...

Thanks, Lee -

Ran across one on eBay, searching for the name. It's on the way. Put the fresh tranny back in my '59, this afternoon, along with the oil tank. First chance I run across some help, I'll put the fresh engine back in. That one may be a booger, as I disassembled it as I went. Only had the bottom end to remove. Now, I've got the whole thing. Should have reinstalled in the same manner. Looking forward to getting the old machine out on the Winter roads, for a cool break-in.

Jack

Jack Hester said...

"Replace the 'clutch hub fiber disc' with the 'Nylatron' unit."

Got the '59 back on the road a couple weeks ago, with one of these disc's installed. Man, what a difference. Shifts smooth into 1rst, no matter the engine RPM at idle. I tend to run my engines with a bit faster idle, than most. Keeps the oil pressure up when the engine/oil is hot. And, finding neutral is a breeze, no matter the idle speed. Thanks for the great tip.

Jack

St.Lee said...

Glad to hear it worked for you, Jack.

Anonymous said...

Lee if I trailer out my bike will you make my suicide 3" BDL clutch not drag and be so grabby? Cause I'm tired of trying to ride it since I rebuilt the engine.

St. Lee said...

Sorry, but I'm set up as a machine shop and don't do any work on anything still in a rolling chassis. These "tips" are all from earlier years experience back when I did service work. A 3" belt drive may be the toughest to deal with. Often they are not adjustable for tension, and are very tight. That will tend to cause binding that may require machining to make the belt adjustable. If you call me, perhaps I can point you to a shop capable of working out the problem.