Front wheel hop... 1977 Bonnie 42K on the speedometer... OKay, I am at whits end. Have done the following: New tire and tube (Dunlop K81), balanced three times, new set of springs, changed fork oil, measured everything that would move and calibrated, ran without brake disc, pumped up tires to 60 pounds, reduced air to 20 pounds, checked bearings and spindle, Tightened steering damper, checked true of wheel, made offerings to the Gods of Triumph, sent my first born on a pilgrimage to Meridan, even offer the wife for a Saturday Night Fling and the damn thing still hops (not the wife) at 40MPH. HELP! Any far flung suggestions would be appreciated.
Next thing on the list will be to change the bearings, but how would the bearings cause wheel hop? With the old Triumph the solution to the problem is always something which seems unrelated. If you are thinking electrical it's usually mechanical. If you are thinking mechanical it's always electrical.
Bent Forks? Nope. Checked the front end. All is where it supposed to be. Wheel hop starts around 40 MPH.
If we are to help most effectively we need more than ‘hop’. ....you might know what you mean by hop but it is open to wide interpretation from patter to suspension that ‘pops’ because the bushings are worn and sticking rather than sliding smoothly. Oscillating, clunking, bar wagging, speed sensitive etc Plus an exhaustive list of what you have AND haven’t done since it was last ‘right’ if it ever has been while you have owned it
Youre hopping around spending money willy nilly ...... start with @Callumity 's plan and work steadily along a logical line of investigation, starting off by describing the problem in more detail so we can try to help in a more informed way.
At 40 MPH the forks start to vibrate and the front wheel begins to bounce. At 60 MPH the same no more no less. Two new tires in the past year, both Dunlop K81 from a supplier in New Jersey. I do not know if they are from the same lot. The first was definitely out of round. The second checked along with the rim and wheel balanced. New bearings were installed along with new fork springs and a new brake disc which was turned and yes the fork oil was changed along with a check of the seals. There appears to be no cracks or anything out of alignment in the front end. Also checked wheel alignment and anything and everything between. The problem started when the first new tire was installed and the mechanic destroyed the dust cover (right side) jamming the spindle. New bearings and spacers were installed and the spindle checked for roundness....... Would defective bearings or damaged spindle cause the problem?
I would strip the forks from the bike and check the legs top n bottom for wear and also the damping units on the bottom of legs
Ok so what happens between 40 & 60 does the hopping continue or does it go away and come back ? Can you describe the "vibration" ..... is it the start of the hop as in up / down and building into the hop or oscillation as in side to side ?
The spindle may be bent. Roll it on something like a big mirror or sheet of glass to check it for true. I am also curious about who/ how the wheel was balanced. Motorcycle wheels are normally balanced radially with limited concern for axial balance but if it is badly out it will be an issue - the new disc could be an issue. A dynamic balancer in a tire shop with a bike wheel adapter will confirm it one way or the other.
If you have checked all the above and they check out ok, it could well be a faulty tyre, check the age on the side of the tyre, there is an oval with 4 digits inside it, like 1217, this means the tyre was made in the 12th week of 2017 if I recall correctly, tyres have a lifetime of about 5 years. Also is the tyre direction correct, there is an arrow showing direction of travel too.
