My 305 scrambler 1967 goes down the road fine at speeds 35 to 40 MPH. When I go up to 45 to 50 MPH in 4th gear the engine is revved up at such high rpms that it feels like the engine is going to fly apart. I thought for a long time that the trans was not shifting into 4th gear but I know now that it is. I pulled the engine out and seperated the casing and looked over the gears. I can't see anything obvious. My concern is that the engine in this bike is not the original and it came from a guy that raced 305 motors in small race cars. My concern is maybe he changed the gears around to suit this type of racer. I counted the shaft rotations while going though all 4 gears and this is what I come up with.
1st gear 1 to 2.75
2nd gear 1 to 1.75
3rd gear 1 to 1.10
4th gear 1 to 1
The minor difference between 3rd and 4th seems wrong. I can tell when shifting into 4th gear there almost no reduction in RPMs. I am running a 15 tooth drive sprocket with a 37 tooth rear sprocket which I beleive is correct for this bike. I have looked though the forums at photos of opened gear boxes and mine appears to look like the others. Can anyone give tell me if these gear ratios are correct? Am I over looking something? Woody
correct gear ratios ?
Re: correct gear ratios ?I'll add now that what has been shown with "G" man and your numbers FINAL IS ALWAYS 1 To 1!.
Look at the engine chain sprocket and the wheel sprocket and count the teeth. Let us know the numbers. ..........lm
Last edited by LOUD MOUSE on Sat Dec 27, 2014 5:00 pm, edited 1 time in total.
The way of evening out the steps in the transmission is to "X" the 2nd and 3rd pairs which gives a better spacing. If you want to reduce the revs in top gear you need a smaller rear sprocket or a bigger front one.
My picture shows the effect of X-ing 2 and 3. The Hawk and scrambler use the same ratios. G
'60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F Loud Mouse, When I brought this bike out of the basement after 45 years it had a 13 tooth drive and I switched over to a 15 tooth drive recently. I never changed the rear which is a 37 tooth. How small of a rear sprocket can you go down?
G-Man, According to you graph my gear sets are right. I just can't beleive that 45 years ago I rode around with the engine screaming at that high of an RPM, but hey I was just a kid. Is X ing having to do with shims? Thanks to both of you guys for your help. Woody
The 305 gears from HONDA issue were 15X37.
You can get Super Hawk rear sprockets down to 30. ..........lm
How many rpms is it actually turning? With 37 teeth on the rear as standard, it should be geared to go about 85 mph (9000rpm), probably run about 6800 rpms at 65 mph.These engines were not intended to be lugged, they will run happily all day at 55-65 mph using standard gearing.
'65 YG1
'65 CB160 '66 CL160 '66 CL77 '78 XS650 '79 GL1000 '69 T100R '68 TR6 '69 T120 '72 750 Commando my company car is a Kenworth 305 gearsMike, I don't know what I had for RPM's but at 50 MPH the engine was screaming. I have the engine apart now. Found the piston skirts pretty scuffed up. One thing that I did that probably has made this worst is that when I changed out the tires I could not find the original size rear and installed a Dunlop K81 4.10. This is a taller profile tire, but could that make that much differance?
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
