Springer Front Fork on a Heathkit Boonie

cfh

Active Member
#1
I have a decent Heathkit Boonie Bike with a 5hp Tecumseh and a TAV30. It works well, but the lack of any real suspension really hampers the usability of this bike (at least for me.) Also the small front wheel makes the bike handle a bit odd.

I was thinking of trying to fix these two issue. Has anyone done this?

On the front fork, was thinking of trying to move the lower triangle plate of the fork upward, to abandon the large (and useless) single spring. The fork tube is pretty short on this bike though. I guess i could increase the length of the fork tube as an alternative? Was wondering if there is some consequence of this i'm not seeing? Then could add a springer front end to this.

On the small front wheel, maybe just bring the front geometry up a bit will make the bike handle better. But what are thoughts on a 10" front wheel? thanks! cfh



 
#2
I feel your pain. Same issue with my Heald VT1.I was thinking of even putting pitbike forks on it but then I remebered that I wanted the old school frame so that was out. I was also going to cut off the pegs and put folding ones on but figured I would just wait until I snap one off. 4857C5A4-056E-4F77-9D28-5534FC567908.jpeg
 
#3
That is a good looking Boonie you have there.

Here's my take on it. I think the Boonie originally was designed with that two speed (selectable only when stopped) transmission so a hunter or fisherman could ride from his truck at a bit of faster speed while the smoother trails allowed. But then when the going got rough, low gear and it's slow speed was selected...really slow...so slow that you really didn't need actual suspension.

With the TAV in your set up, I think it allows for way faster speeds, than the two speed transmission ever would have, thus pushing the limits on the little fork tube single spring.

All that said, I am not discouraging you from creating a suspension solution. It would be neat to see it done while keeping the same stance. And goodness knows it would feel better...:laugh:

If I recall right, someone on here recently did a modification where they created an internal suspension system on a previously rigid front end, by cutting the fork tubes at some point, using smaller diameter inside fork tubes they fabricated with internal springs above them. It provided suspension, but kept that bike looking factory to me.

Regarding the handling...I think your suspension solution will help that greatly. But here's something else to consider...it may not be the size of the front tire, but the shape of it, you know the footprint...it's flat as can be. I know my Boonie Bike will almost stand up by itself, without it's kickstand, with the wide almost flat shaped foot print of the rear tire, and the front tire's definitely flat shaped footprint. When rolling, it will almost 'steer' itself. Perhaps try a front tire of the same size, but with a curved transition to the sidewall, as opposed to an almost 90 degree transition to the sidewall of the original tire.

Let us know what you do, and how it rides.
 
#4
I have one of those Boonie Bikes and Robert is right about the flat profile of those front tires. Using a front wheel with a rounded tread profile will improve the steering very much.
 

cfh

Active Member
#5
Yea i was the one that added a springer front end to a Harrison Wildcat and posted the details here.
https://www.oldminibikes.com/forum/index.php?threads/harrison-wildcat-mods.164582/
In comparison though, that's probably an easy modification on the Harrision. The problem with the Boonie bike is the existing center spring. How do we work around that? I would like to cut the bottom triangle and move it up (which would eliminate the stock center front end spring).... then add the springers to the fork tubes. But could also just lengthen the neck tube and not mess with the stock triangle front end... Just not sure which way to go. Was hoping someone has done this before and has some ideas. thanks! cfh
 

pomfish

Active Member
#6
Alright,
Nice bike.
Pretty much think from your OP that you are not concerned to to a little cutting/modding to this bike to get it to your liking.
Love that attitude, it's your's make it how you want.


RobertC is dead on about the profile and design of the current tires, they were made for lawn equipment/tractors that turn at 4-7 mph.
Now, the other big part of the problem with these old bikes are the Old Tires, they are hard as a rock from drying out with age.
Don't fret over the bolt spring, let it there for now.
Would suggest moving the front fender all the way up to the bottom of the triple tree for more clearance and then use a 10 inch rim with a new high quality low pressure rounded edge tire. If the 10" will not clear go with a 8" with the biggest profile for more ground clearance.
Replace the rear tire with same style low pressure tire and the ride is going to improve big time.

I say quality tire because these modern china baja's motovox, etc have tires that are not round, not balanced etc.
What passes QC is a joke.
Pay the money for a good tire and never look back. Have the tire shop balance them as well.

Other members can probably recommend you a good tire choice but for sure both tires need to go.
I have a Boonie style bike with rear suspension and it has that same big Goodyear ear tire and as someone else has said the bike will stand on it's own if on flat ground because the tire profile is so flat and the sidewalls are that stiff.

Anyway, Good Luck and show us the results when you modify her.
Later

Keith
 
#7
For removing the spring, I would play around with the idea of replacing the spring with a piece of tubing with the same length as the spring.
 

cfh

Active Member
#8
I was thinking about replacing the single center spring with a 2 inch piece of tubing. But there are some disadvantages to that. For one I don’t think it makes the front end more stable. And two I don’t think it gives you enough room for the forks to move in a Springer situation
 

cfh

Active Member
#9
Some more things to think about...
My local buddy Frank suggested I cut off the original handle bars and put a block and new style bars on the bike (kind of Harrison style handlebars.) He said this makes a huge difference in the handling, especially at higher speeds.

He also said the issue with the front tire is a huge deal.... and one not easy to solve. it does needs a better tire, but nearly all replacements will be too wide, and rub on the sides of the fork tubes.

His suggestion is to make an entirely new triple tree, using a Harrison style parts (which conveniently he sells!) This will increase the width of the fork and allow for a wider front tire style. And at the same time, make it a springer. About a $100 in parts for the whole get-up (including the springer parts.) I would have to weld it (no big deal as i do that.)

Though he is probably correct on all accounts, i thought i would walk this process in a more slow manner, and try and modify the original Heathkit Boonie front end.... I can always make a new Harrison style front end later...
 

cfh

Active Member
#10
I decided to abandon the single fork tube spring, and move the lower tree plate. The measurement of the neck tube is 5" long, plus a 2" spring. Meaning the distance between the top and lower triple tree plates is 7". This needs to be reduced to 5". But we also want a 2" tube extend beyond the lower plate. So this works out really well. Just use the Mataba saw and cut the fork tube, right through the lower plate welds. With just a bit of additional grinding, the lower triple tree plate is loose, and can be moved to a 5" inside distance. Then it can be re-welded (and spring cups added.)













 

cfh

Active Member
#11
Now to figure out where the lower springer cups should be mounted (and how much to cut off the lower fork tubes.) Here's a mock up of where might be a good spot for the cups. Though in these two pictures the fork tubes are not cut, and the 11/16" solid bars have not been welded into position. It shows how the front end will be raised (about 2" higher). The lower fork tubes look like they need about 1" cut off.

Of course this does not solve the tire width issue... but this does increase the fork rake, which may help thing, even with the stock tire.



 
#13
I have 2 boonies. I attributed the poor handling and self steering to the giant flat rear tire. And not so much the front tire. I even put slightly smaller rounder tire on front but mine still stands on its own. Still not quick Turner. Just love for the cruising. Good luck with enhancements. Love the bikes
 

cfh

Active Member
#15
I bought the new handlebars and handlebar block today. I'm just a bit hesitant about cutting the original bars off the triple tree. I know they are terrible bars, a bad bend for any sort of speed or handling. I'm just a bit nervous because once i cut them, they are gone forever! And it will change the look of the boonie...
 

delray

Well-Known Member
#16
looks good, now you got to get that 12v starter/battery/electric start and correct vintage style headlight and tail light mount on it. ….

do get the wrong impression,why do you keep posting your projects/builds under mini bike discussion?
 

cfh

Active Member
#17
why do i post it here? because i was hoping for a discussion on how to approach these issues/problems. unfortunately it's tough to get people who have experience in this type of stuff to post. i can't believe i'm the first guy to ever think about doing these types of modifications to these styles of bikes... it seems the guys that have done this stuff just don't post about it, or don't see the posts.

on the light issue... i'm not big on lights. i don't ride at night. and it's hard to get vintage tecumseh hs40/hs50 motors with lighting coils too.
 
#18
Another option is to Fab up a completely new set of forks with the internal spring setup similar to the Bonanzas and others. Maybe use 7/8" o.d. x .083 wall tubing for the lowers and use 1 1/8" o.d. x .095 wall for the upper tubes. Spring is hidden so it could retain some of the "look". Although you would still need bolt on bars
 

cfh

Active Member
#19
Pat i may end up doing that. the local parts guy sells the parts to make a new triple tree with springer style forks. all the parts are about $110, just need to weld it up. seems a bit pricey, but it would allow for a wider front tire. I already bought the bolt-on handlebars and block, so i have that. was going to try that on my original/modified springer boonie set up. figure i have nothing to loose at this point i guess.

right now i'm just trying to get myself to the point where i can get the balls to cut off the original handlebars.... i'm just worried that once i do that, there's no going back!
 

delray

Well-Known Member
#20
why do i post it here? because i was hoping for a discussion on how to approach these issues/problems. unfortunately it's tough to get people who have experience in this type of stuff to post. i can't believe i'm the first guy to ever think about doing these types of modifications to these styles of bikes... it seems the guys that have done this stuff just don't post about it, or don't see the posts.

on the light issue... i'm not big on lights. i don't ride at night. and it's hard to get vintage tecumseh hs40/hs50 motors with lighting coils too.
it's been done before and you being a newer guy your not going to find any old posting real easy. not sure because of way the new forum is or what? somethings I try to find from the past and just can't find them very easy.
 

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