Here are the dimensions of CB750K SOHC springs compared to CA77(2 versions), and a pic of CB750 Spring in the CA basket.
As you can see, there are differences in free length, wire thicknesses and coil spacing, with any of the three affecting the final installed spring pressure.
The shop manual specs for the spring tension are a little confusing to me.
The C72 specs state "15# at 25mm(.98 of binding length)" and "33-36# at 23mm(.90 max lift)"
The C77 specs state "33.7-34.6#" with no measurement lengths listed.
I will try to measure the tension at the installed length of each to see just how much difference there is.
Clutch Spring Differences CA77
I asked those questions as ya described installing the bolt.
The clutch came/comes with 6X16mm bolts (as brewsky shows) they will/should allow the bolt to screw in long before the bolt top contacts the washer threads to come in contact. The brewsky pic shows a lot less than 16mm of spring exposed above the pressure plate. Had ya changed the length of the bolt also to cause you to need to compress the spring for the threads to come on contact. ...........................lm
Last edited by LOUD MOUSE on Sat Mar 06, 2010 11:03 am, edited 1 time in total.
Inquiring minds want to know...
As I said before, the springs are already in the motor, so we'll all have to wait until I get back to Australia and have a chance to strip the clutch cover off to measure those springs. Then I will have a record too. All I can tell you for sure is that the springs were much longer and were more open that stock springs and came with top hat type thin steel caps. The springs were not "gold" like Barnetts but more of a dark blue/black IIRC. I bought several sets from Norris Cams when they were still in business but have no idea who their suppliers were. I measured the compressed length of the springs as installed in the basket with plates in and got an even 1.00".
I then used a custom spring tension measuring device to measure the tension of each of the 3 springs shown on the previous pics, compressed to a length of 1". Results: Shortest spring (supplied by Loud Mouse).................54# Medium length spring (removed from my CA77).......32# Long spring (from CB750K sohc).............................51# It should be noted that the scale used to take the measurements is probably not very accurate, so the absolute numbers may be suspect, but should at least show the relative differences. I also noted that Silver's book mentions the possibility of using DOHC 750 springs not SOHC 750, and I have no idea the length etc of those. Also, the long CB750 springs will allow the bolts to begin threading before the spring begins to compress. Now to install the short ones and see what happens. 66 dream, 78 cb750k, 02fz1, 09 wing
It has been a long time since I worked with spring theory, so there's a high probability I'll screw this up, but let's see how far we get.
The short spring was compressed from 1.26" to 1.00 inches and showed a pressure of 54 pounds. That makes a spring rate of 54/0.26 = 207 pounds/inch The medium one compressed 0.36" and was at 32 pounds or 88 pounds/inch The long one compressed 0.56 and was at 51 pounds or 91 pounds/inch. The numbers don't sound quite right, but the principle is right. the short stiff spring creates almost the same pressure on the plates as the CB750 spring but is MUCH stiffer to pull. If the CB750 spring was say 2.0"" long, the pressure would be 180 pounds but it would still have a light pull at the lever. That is why it is better to use a longer lighter spring than a short stiff one. Of course if I remembered that wrong, the whole argument could go up in smoke, but it sounds right
What I have to offer on this subject I will show with a pic and description as to how I find they work when used in a CB/CL72/77 engine.
#1 is a stock HONDA spring used in the early years and is the tallest with the thinnest wire of the stock/standard CB/CL springs I've removed from engines. It is easy to release the clutch but my experience is it doesn't engage the clutch well and will in time allow the disc to ware and the clutch to slip. #2 is the white paint on one end (1966/1967??) issue and does pull a little harder than #1 but gives a good feel at the lever as ya release it and the clutch disc engage smoothly and firm and no problem with the disc #3 is the 810 HONDA issue and is the hardest of the 3 to release but gives a similar engagement as #2. It is the shortest and has the thickest wire of the three. This info is from using each of these springs at one time or another as I've owned/ridden the bikes with these springs in the clutch. No pressure measurement with tools just use over the years. I install the #2 springs in all the rebuilds I do at this time. ............lm
I was back in Australia recently and had the opportunity to strip the clutch and trans and offer the following dimensions for your edification and amusement.
Barnett MT10 Length 37.6mm Diameter 18mm, wire thickness 2.64mm Norris SOHC Length 47.6mm, diameter 19mm, wire thickness 2.3mm You may remember that I mentioned that the springs were so long that they had to be compressed slightly to start them, now you can see why. They are really long but not a very high poundage rate, so they clamp tight but have quite a light pull. I'll try to add a picture as soon as I sort through all the shots I took.
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