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How fast is a 45?

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45Brit

Posts: 1416

Joined: Tue Nov 27, 2007 2:29 am

Post Sat Aug 23, 2014 12:20 pm

How fast is a 45?

I've just been reading a back issue of Greasy Kulture, featuring a road-legal bike based on WR cases, stroked to around 53ci

I'm interested to see that the builder states that he has so far been timed at 86mph using a GPS speedo, and reckons to see 90mph soon.

So, how fast is a flathead? I don't want unsubstantiated claims, or good oi' boy stories, but actual proven figures.

I've reckoned over time that a military spec WL is good for something over 65mph and comfy at 50-55mph, which would be comparable to British 350cc-500cc ohv singles of the era. Lightening the bike a little and raising the gearing might get a genuine 5-6 mph more.

My original Ariel-framed WL was timed at 81mph at Snetterton, flat out with rider in leathers at a VMCC road racing event. That's a bike about 85lb lighter than a WL, fitted with an Amal carb, geared at about 20% higher than a stock WL and given that the Triumph 5T would just about do 90mph with 26-27bhp and a lighter bike, it seems about right. It would certainly do a genuine 75mph in road trim.

I've seen WRs quoted as making 40bhp, and being capable of 105mph, which seems a feasible combination provided the power output is true.

So, what will a 45 really do, either in stock firm or stroked?
Shoot, a man could have a good weekend in Dallas with all that stuff...
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ozihotrod

Posts: 72

Joined: Mon Apr 17, 2006 9:13 pm

Location: South Australia

Post Sun Aug 24, 2014 5:45 am

Re: How fast is a 45?

i have just purchased a small GPS to use as a speedo for my WL's, went for a ride yesterday on one of them, my wl , with WLDR cams, 36mm Mikuni and the other usual motor mods was doing 125Kph on the flat easy, still with more to go, I had to back off as i was 15Kph over the road limit and did not want to get busted for speeding on a 72 year old bike, im keen to try my 900cc stroker with KHK cam to see how it goes..Image
" The more I learn the less I know"
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Pa

Site Admin

Posts: 4700

Joined: Sun Mar 12, 2000 1:01 am

Location: Ohio USA

Post Sun Aug 24, 2014 11:15 am

Re: How fast is a 45?

Try a forum search using different forms of search criteria. Many years ago there was a post by a member which had his 45 doing well over 80mph. He did have mods but none were to drastic.
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45Brit

Posts: 1416

Joined: Tue Nov 27, 2007 2:29 am

Post Mon Aug 25, 2014 4:20 am

Re: How fast is a 45?

I've tried to do that, but I can't find any combinations of words that are specific enough to return useful results. Plus, a good deal of what is posted can best be described as "unsubstantiated"

My best estimate, which ozihotrod seems to be agreeing with, is that a lightened 45 with some simple mods such as WLDR cams, a better carb, probably 6:1 heads? and tyres in the 3.25-400 range is capable of 80-plus mph without serious mechanical distress.

I estimated, when I started my Ariel framed project, that the bike would be capable of 85-90mph with stroked flywheels, 6:1 heads, WLDR cams and an Amal, and the GK bike seems to bear that out.

Personally, I think 85mph on a 70 year old bike, with a rigid frame, drum brakes and springer or 1950s tele forks is enough ...
Shoot, a man could have a good weekend in Dallas with all that stuff...
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ohio-rider

Posts: 231

Joined: Tue Jun 12, 2007 7:26 am

Location: Ohio

Post Mon Aug 25, 2014 6:35 am

Re: How fast is a 45?

Wow, you guys are doing a lot better than me. My 45 with a fresh rebuild has the standard bore with no special cams or any such things. The best I’ve gotten out of her is 72mph with my 180lbs on her back and it took a while to get her up to that speed. It will cruise all day at 60mph but at 72mph it starts to sound a little frightening.
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45Brit

Posts: 1416

Joined: Tue Nov 27, 2007 2:29 am

Post Mon Aug 25, 2014 8:38 am

Re: How fast is a 45?

72mph sounds about right for a stock spec 45.

Most seem to agree that #6 heads and WLDR cams make a considerable difference
Shoot, a man could have a good weekend in Dallas with all that stuff...
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Frankenstein

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Location: Interlaken, NY USA

Post Wed Aug 27, 2014 8:14 pm

Re: How fast is a 45?

Frankie pulls the Ton according to the Smith's chronometric fitted. That's 5k rpm by the similar tach.
DD
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45Brit

Posts: 1416

Joined: Tue Nov 27, 2007 2:29 am

Post Thu Aug 28, 2014 12:00 am

Re: How fast is a 45?

Frankenstein wrote:Frankie pulls the Ton according to the Smith's chronometric fitted. That's 5k rpm by the similar tach.
DD


What front sprocket does it have? Eddie Dow (the BSA tuning guru of the day) quotes the Rocket Gold Star as making 40bhp at 6800 rpm and states that some versions can achieve 45bhp at 7500rpm.... so 100mph at 5000 rpm indicates a front sprocket of about 25/26 teeth, assuming a 19 tooth gearbox sprocket? Am I right in thinking a Frankenstein has a BSA mainshaft and alternator?

I'm always cagey about accepting speedo readings, and that includes Smiths Chronometrics (which had no great reputation over here, for accuracy, regardless of the name). Quite apart from anything else, there are numerous combinations of speedo head, gearbox sprocket, rear wheel sprocket, rim size and speedo gearbox drive which all fit together but don't provide a true speedo reading.

So speedo readings from modified bikes are out of court.... since you presumably know your gearing and wheel sizes, hw does 5000 rpm calculate?
Shoot, a man could have a good weekend in Dallas with all that stuff...
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Frankenstein

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Location: Interlaken, NY USA

Post Sun Aug 31, 2014 1:19 am

Re: How fast is a 45?

So, it took awhile to dig up the info on Frankie, been awhile since I put it all together. Overall gearing is about 3.7 to one. Front sprocket is 23T, clutch basket, 43, tranny sprocket 24, and rear is 48. Made my own overlay for the tranny sprocket from a stock sprocket and a H-D 24T item. Rear wheel 18" about 28.5" tall. So, problem is, we're still back to trusting a Smith's instrument for Engine rpms. I've done enough side by side running over the years to feel the speed data is fairly close. This from Riding with a variety of other machines, and the roadside radar readouts we have in the States these days. It would ride fairly even with my Buddy's Goldie on secondary roads, no chance to do a top end run together. Entirely different engine characteristics for sure :lol:
The Speedo and rear wheel speedo drive take off I took as a unit from an old rolling RE 500 chassis I acquired back in the day. Both looked to have been together since leaving the factory.
Frankie truly is a "Frankenstein" of parts never envisioned as being together from disparate sources.
Or maybe a more apt way of putting it is if there was a hard way of doing it, that's how it got done when I built it :lol:

Oh yes, the mainshaft is from a magdyno B33, the Lucas alternator was turned down (thinned) and the center bore reamed to a very tight press fit on the mainshaft. No Key was used, didn't want to cut a keyway in a mainshaft that I feared was barely adequate to the job at hand. The mainshaft was a difficult part of the build. I didn't have the resources to do it myself, and finding a machinist who could give me an accurate taper on the flywheel end of the BSA shaft took 3 tries. But in the end we found one and the shaft has taken the beating issued for years and miles now.
DD
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45Brit

Posts: 1416

Joined: Tue Nov 27, 2007 2:29 am

Post Sun Aug 31, 2014 6:57 am

Re: How fast is a 45?

According to my trusty fag packet, 5000 rpm means rear wheel speed = 1351rpm

28.5" gives a circumference of 89.5" = 10078.93 ft/min = 114mph or something like it, which sounds like a genuine 100-plus

I'd realised there must be a special sprocket somewhere - why the gearbox? Alternator clearances?
Shoot, a man could have a good weekend in Dallas with all that stuff...
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Frankenstein

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Location: Interlaken, NY USA

Post Sun Aug 31, 2014 7:29 am

Re: How fast is a 45?

That just seemed to be the logical place. The engine sprocket uses the standard compensator setup, the alternator being sandwiched between the engine and the inner primary case. I guess I just copied the typical Harley setup, and there was plenty of room for the sprocket at that location.
Like the colloquialism, "fag packet calculator", over here the nearest to it would be "back of a napkin". vive la difference.
And now a sad commentary on the U.S. The auto spell check only shows the Spanish "Viva" to correct my French.
DD
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45Brit

Posts: 1416

Joined: Tue Nov 27, 2007 2:29 am

Post Sun Aug 31, 2014 12:12 pm

Re: How fast is a 45?

I had quite forgotten that the alternator A/B series BSAs had the compensated sprocket.

There ARE gearbox sprockets up to 24/25 teeth available but they aren't easy to find. FWIW, and digressing a little I would always recommend the AMC gearbox and clutch for project bikes of this sort - they are more compact than the BSA ones, they are very robust and the later Commandos used sprockets up to 25 T, having run out of space around the alternator.

My Ariel-framed project bike has a BSA box but I also have a shaft designed to take a Norton clutch, a grasstrack racing part.
Shoot, a man could have a good weekend in Dallas with all that stuff...
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Pa

Site Admin

Posts: 4700

Joined: Sun Mar 12, 2000 1:01 am

Location: Ohio USA

Post Tue Sep 02, 2014 6:52 am

Re: How fast is a 45?

This should answer the question of how fast. His top speed was 120.142 MPH.

https://www.youtube.com/watch?v=JRzfGkr8avY
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37ULH

Posts: 684

Joined: Mon Nov 25, 2002 1:01 am

Location: somerset, oh usa

Post Tue Sep 02, 2014 4:42 pm

Re: How fast is a 45?

built a complete bike about 5 years ago using a stock 45 frame, trans, stock stroke lower end, 45" K top end, khk lobes, m53 carby, k front end, and took it to a sanctioned speed run fresh with no testing other than, will it run and does it have 3 gears.
First time we pulled the trigger on it with no testing other than the above, it averaged 96mph through the traps and the throttle was closed allowing the rpm to drop 3 times while going down the track. (standing mile)
I have not run it in a timed event again yet but hopeful to put it back on the track next year.
I am relatively certain that it will top 100.
It ran in a 500cc class as they adhere to the 500 / 750 rules
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45Brit

Posts: 1416

Joined: Tue Nov 27, 2007 2:29 am

Post Tue Sep 02, 2014 8:41 pm

Re: How fast is a 45?

What particularly surprises me about that bike on the salt, is how easily it starts.

Sounds like I need to make some workshop room for my project bikes...
Shoot, a man could have a good weekend in Dallas with all that stuff...
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ozihotrod

Posts: 72

Joined: Mon Apr 17, 2006 9:13 pm

Location: South Australia

Post Fri Sep 05, 2014 5:51 am

Re: How fast is a 45?

There is a WL that has been timed here in South Australia on the salt in 2006,
it ran in 500cc MVG class, and was timed at 106 MPH, so this still hope for us street Walla riders .
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" The more I learn the less I know"
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knucklebolt

Posts: 212

Joined: Tue Feb 12, 2013 8:27 pm

Location: Six miles East of Cheney, Wa.

Post Sun Sep 21, 2014 5:00 pm

Re: How fast is a 45?

Doesn't the flathead/knuclehead big twin motor sprocket fit on the 45? I had a sprocket made for my 45 when I put the big twin gear box on it, and it seems that I later noticed that a big twin sprocket would have fit, after I paid a machine shop to do that. Possibly my memory fails me on this. !!!!

My point being, that big tooth early big twin sprockets are easy and cheap to find...assuming they fit, which they may not, that memory thing again, or perhaps the offset is wrong.

k.
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45Brit

Posts: 1416

Joined: Tue Nov 27, 2007 2:29 am

Post Wed Sep 24, 2014 12:22 pm

Re: How fast is a 45?

:( I don't know about BT sprockets fitting 45s but I do know that Paughco list a bigger size sprocket for that conversion, so I'm guessing that BT ones don't fit. They can also be used for fitting some Britush gearboxes
Shoot, a man could have a good weekend in Dallas with all that stuff...
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jib

Posts: 572

Joined: Sat Dec 10, 2005 3:36 pm

Location: devon,england

Post Tue Sep 30, 2014 4:20 pm

Re: How fast is a 45?

clocked by a standard v rod at 90mph ,then accelerated to a shown 85mph on my speedo. 18 rear wheel with 130 avon distanzia tyre.

at 60mph on my speedo -the v rod speedo showed 70

at 70 on my speedo - the v rod showed 90.

this was during a ten mile run ,on two lane black top. we averaged 70-80 most of the time .


althougth its no lazer speed trap i reckon that accurate enougth for me ,until i can get somewhere that does timed miles.
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years

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