Changing the Stall Speed on Grubee Clutch

Discussion in '4-Stroke Engines' started by ocscully, Oct 21, 2010.

  1. ocscully

    ocscully Member

    First let me say that the following information applies only to the New Clutch supplied by Grubee and for the Honda 4G drives and and as a replacement clutch for the Type II & III Gearboxs. This new clutch has alot to like in the way of improvements over the older design clutch, but it has one major flaw, as supplied from Grubee/bicycle-engines its stall speed/engagement rpm is dangeriously low. Far worse that the old style clutch. At first I tried drilling lightening holes but the change was insignificant. (first photo below) Then I started looking into changing the springs. The clutch uses three small compression springs to control/set the stall speed/engagement. (second photo below) To start with I needed to determine the dimensions and spring rate of the original springs so I could find and purchase springs that would fit and had a higher spring rate. The original springs are .520in. OD X .780in. Long. and I determined the spring rate to be 40lbs/in. I found a set of 47lbs/in. springs at a local industrial hardware store and tried them out in the lightened clutch. The result was better (the motor no longer died when I came to a stop) but still the clutch was to grabby at idle and still took off like a jack rabbit when first started. The local store didn't have any springs that would fit stronger than the 47lbs ones so I tracked down a local spring mfg. (LA) Century Spring Corp. They had several springs in their catalog that seemed like they might fit my needs. So I made a trip to LA to buy more Springs. I figured I needed and additional 10lbs-15lbs of spring rate. I ended up buying a set of 57lbs/in. and a set of 60lbs/in. springs. The 57lbs springs work well in the lightened clutch and the 60lbs work well in the clutch without the lightening holes. The Last two photos below show the various springs from top and side views. From left to right they are 40lbs/in. stock springs, 47lbs/in., 57lbs/in., and 60lbs/in.


    Attached Files:

    Last edited: Oct 21, 2010

  2. RdKryton

    RdKryton Active Member

  3. ocscully

    ocscully Member

    Jim ,

    No that isn't the same source I used. This should take you to the company I used. I did not provide a link earlier or actual part #'s purchased because the company has a $40.00 minimum for orders placed over the phone or online. They waive the minimum if you order and pick up at their Will Call Desk. If you think it would be helpful I'll provide part #'s?

  4. 4G stall speed

    My 4G had the exact problems as yours. I too blamed the springs untill I did away with the stock bushing and replaced with one that I got from Mc master Carr. Its a true SAE oil Lite bushing.The grabbing and taking off fast when started and dying when coming to a stop were no longer a problem. Motomagz has the tranny now
  5. RdKryton

    RdKryton Active Member

    Yes please supply the part number. Maybe a few owners will get together or even a vendor may be able to justify a large enough order to meet the the $40.00 minimum.

  6. MotoMagz

    MotoMagz Member

    Yes I have Bills old 4G with the oil lite bushing.I was not experiencing any hopping when taking off.I was experiencing terrible clutch bell ringing and not being able to turn down the idle without it stalling.Also it just was not safe.Yes I have the 60lb springs in my clutch thanx to my Scully and his research.When I first started my engine after installing the new springs I was amazed and confussed.I thought I had forgot to secure something?? It was just to I gave her a little gas while up on the stand.There it was perfection! For the first time in 4 or 5 years a low idle and a clutch not engaged.I have the shift kit with the narrow 4G and will try to get a video up so everyone can see how well these new springs work.
  7. ocscully

    ocscully Member

    The Springs I finally settled on are Part # J-37 from Century Spring Corp. the dimensions are as follows, .562in. OD X .88in. length, 60lbs/in. Spring Rate, .067in. wire dia. , made with Spring Steel that has a Zinc coating. The cost per spring was $2.50ea. There are price breaks beginning at 10 pieces or more.