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MAC tuning #761270
01/02/19 5:04 pm
01/02/19 5:04 pm
Joined: Dec 2018
Posts: 39
UK
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Project ROTM Offline OP
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Good afternoon,

I am currently undertaking a project to see how fast I can make my Velocette MAC go. I have started a thread in the projects section.

I was hoping people might be able to share their experience of tuning MAC engines?

Kind regards,

Project ROTM

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Re: MAC tuning [Re: Project ROTM] #761292
01/02/19 9:29 pm
01/02/19 9:29 pm
Joined: Jul 2016
Posts: 243
Australia
Joolstacho Offline
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Australia
You can prep an iron MAC so that it goes pretty hard, 100mph not out of the question.
M17/8 cam, higher compression ratio, bit of porting, decent carb, zorst, simple mods to the lubrication system, EG 2-start oil pump worm, later type timing cover to give better lubrication to the camshaft.
But it leaves the gearbox mounting with it's single adjustable mount on top vulnerable to twisting and potentially breaking the shell.
On mine I added (welded on) a second top mount on the gearbox shell and used x 2 left hand gearbox adjuster plates, one on each side.
I'll see if I can find my notes on how I did mine.

Note (I was told) that the iron MAC motor is a better proposition for tuning than the alloy MAC.
Can't remember the reason behind this though.

Re: MAC tuning [Re: Project ROTM] #761766
01/06/19 8:35 pm
01/06/19 8:35 pm
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Thanks Joolstacho, that sounds like some good advice. If you could find your notes that would be amazing.

I wonder why you have heard of better results with the iron MAC?

I now have a spare engine so I can start stripping it and seeing where improvements can be made. I have an M17-8 cam and have researched using a Triumph piston to increase the CR. I imagine it might be a fine balance between timing, CR and valve to valve and valve to piston clearance.

The second of my build videos is online now if you are interested.



Any advice welcomed.

Thanks,

Project ROTM

Re: MAC tuning [Re: Project ROTM] #761809
01/07/19 11:00 am
01/07/19 11:00 am
Joined: Dec 2004
Posts: 9,926
Scotland
kommando Online content
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Iron heads heat up too quickly, but if say the iron head has better breathing than the alloy head then for short high speed runs that should not matter or if you use methanol (different class ?). I would want to know why the iron head is allegedly better before deciding what to do, first mention of an Iron head being better than alloy I have seen but odd things can happen.

Re: MAC tuning [Re: Project ROTM] #761828
01/07/19 5:31 pm
01/07/19 5:31 pm
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Posts: 52
CALIFORNIA
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slow learner Offline
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Iron head has 15 degree intake tract inclination, alloy head is only 7 degree. Iron head has pressure oil feed to the rocker shafts, alloy head is drip feed but can be modified. In Australia and New Zealand where lots of iron MACs are raced they usually run them on methanol so cooling is not a problem. I knew a pretty successful tuner (AJ Lewis} who preferred iron heads on any motor he built. He was given a Triumph GP by the factory and gave them back the head and barrel. One year his bike finished top three at Daytona when the Norton Manxs where running (that was after his rider crashed and restarted).


Laurence Luce
Re: MAC tuning [Re: Project ROTM] #761847
01/07/19 8:48 pm
01/07/19 8:48 pm
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Thanks for the info Kommando and Slow learner.

I am have 2 spare aluminium heads, so I am hoping to be able to flow them and see if they can be improved upon.

I am planning to run on pump fuel to start with, but maybe I should keep an eye out for an iron head, even if it is just to test it and see how it flows.

Project ROTM

Re: MAC tuning [Re: Project ROTM] #761868
01/08/19 1:34 am
01/08/19 1:34 am
Joined: Jul 2016
Posts: 243
Australia
Joolstacho Offline
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Don't ignore the fact that the iron head has no rockerbox cover, the valvesprings are pretty much exposed, which means that cooling air can get MUCH deeper through the head.

But you've got a couple of alloy Mac donks there so you'll probably want to work with them. (It may be the better downdraft angle with the iron head that is good).
I was advised by a couple of ol' blokes (when I wasn't an ol' bloke!) One was Eric Bushell If I remember rightly. He is (was) a Mac racing guru. The other feller was a Tasmanian who had very good results in Tassie.
I'm still searching for Eric's letter, but my above post explains the important stuff. Yes a Triumph piston -can't remember which, fits and ups the compression ratio, I think I got around 9.?:1.
My carb was 1 1/16" same as Viper - and I'd reckon viper settings would be a good starting point.
I think I used a Viper exhaust valve (Nimonic 80) - It might have been turned down).
I timed at 38 deg with no manual adjustment - fixed timing using a Criterion alloy mag pinion. W & S Valvesprings. Roller (converted) clutch release bearing. I think I fitted a 7 plate clutch (KSS) but not sure about that.

That exhaust... (well you asked for opinions!) - Rip off the kickstart assy (they're pretty useless anyway due to low gearing and big overlap of the M17/8 camshaft). Put on a banking plate and bump-start it (or make a roller paddock starter) -Then you can use a KTT bend or maybe a Manx norton bend, both of which should tuck in much better and give good clearance. (And look dead sexy into the bargain!)
I can't quite see what gearbox you're using, if it's iron Mac it will have the selector lever on the front face. Early MSS / KSS will have the selector on the rear face.
The MAC gears are narrower, but if they're in good condition I don't see why you couldn't use them... the 'box would be a bit lighter eh? - and bear in mind my earlier point about adding a second top gearbox mount if it's the iron MAC shell.

You'll need (at least one) good brake. The 7" SLS Velo brake can be very effective, but I'd certainly machine relined shoes to ensure complete drum contact.

If I think of anything else I let you know. Reminder - I am no expert, and I'm relying on unreliable memory!!!
I think it's good to see a younger guy doing a Velo project rather than 'bobbing' CX Hondas!

-Jools


Last edited by Joolstacho; 01/08/19 2:27 am. Reason: Extra detail added
Re: MAC tuning [Re: Project ROTM] #761915
01/08/19 12:09 pm
01/08/19 12:09 pm
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Thank you for all of the input so far. I really appreciate the advice.

Keep it coming.

Project ROTM

Re: MAC tuning [Re: Project ROTM] #764371
02/03/19 2:36 pm
02/03/19 2:36 pm
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I have just finished the 2nd part of my project video where I try to start the bike for the first time.

eek



Let me know what you think.

Cheers,

Christian

Re: MAC tuning [Re: Project ROTM] #764392
02/03/19 5:40 pm
02/03/19 5:40 pm
Joined: Dec 2004
Posts: 9,926
Scotland
kommando Online content
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There is an art to starting a single which you have picked up well but there are a couple of wrinkles that can help further

The Velocette kickstart is very low geared compared to other bikes, so unlike other singles you need to move the piston further on than just over compression so the energy you push into the flywheel is enough to get the piston over the next TDC, only practise will tell you how far to go, too far and the next TDC will be too near and you will get a kickback, so experiment carefully with strong boots.

On the carb if you use the throttle stop screw to set a fast idle when the bike is cold and then you can leave the throttle untouched. That saves the guesswork in exactly how much throttle to give the bike and reduce the risk of you altering the opening during the kick, too much throttle risks a kickback. As the bike warms you can back off the throttle stop screw until its at its warm setting, for cold starts screw it in 1/2 to a full turn, experimentation will tell you the best setting. If you have manual advance then 1/2 way advanced is good for starting.

Every engine is different so what works for one Velo may not work for another, singles of all makes seem to vary more than engines with 2 or more pistons.

Re: MAC tuning [Re: Project ROTM] #764447
02/04/19 12:36 am
02/04/19 12:36 am
Joined: Dec 2013
Posts: 4,886
ohio, usa
kevin roberts Online content

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christian, you only posted some three seconds of the running engine.

lots more, please.


every day you do not take a chance is a day of your life that you will never get back.
Re: MAC tuning [Re: Project ROTM] #764456
02/04/19 1:46 am
02/04/19 1:46 am
Joined: Jul 2016
Posts: 243
Australia
Joolstacho Offline
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Australia
Goodonya Chris... I like the amazed look on your face when it did go.
And we might have got only 3 seconds of motor run, but I'm sure that was because Chris had to quickly check the oil return in the oil tank :-)
(Weren't you mate).

Re: MAC tuning [Re: Project ROTM] #764564
02/05/19 8:39 am
02/05/19 8:39 am
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Thanks for your feedback, and also your very useful advice.

Unfortunately the camera ran out of battery which is why the footage of the bike actually running was cut short. I will definitely post more.

I can;t wait to go for a first run now!

Cheers,

Christian

Re: MAC tuning [Re: Project ROTM] #764565
02/05/19 9:09 am
02/05/19 9:09 am
Joined: Jul 2016
Posts: 243
Australia
Joolstacho Offline
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Australia
Yes, and maybe run it a little faster at tickover initially to warm it up and get that oil pump pumping black stuff around, and check the oil return in the oil tank. (It doesn't need to be a continuous high flow, it tends to spurt and dribble a bit).
Sorry to state the obvious, I'm sure you don't need gratuitous advice... but it's always worth re-iterating. Crack the oil feed up top at the rockers to check that it's pumping up there too. (Then re-nip it).
Good stuff Chris.

Re: MAC tuning [Re: Project ROTM] #764881
02/08/19 10:33 pm
02/08/19 10:33 pm
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I thought I should get some practice starting the bike. Oil flow to the tank seems good. Heres a short clip for everyone that wanted to see more running. P.S. if you haven't already subscribed to my channel, please do.



Christian

Re: MAC tuning [Re: Project ROTM] #766924
03/02/19 3:02 pm
03/02/19 3:02 pm
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Here is the latest instalment of my Velocette speed project. Don't forget to subscribe.



Christian

Re: MAC tuning [Re: Project ROTM] #769019
03/23/19 11:05 pm
03/23/19 11:05 pm
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Re: MAC tuning [Re: Project ROTM] #769035
03/24/19 1:11 am
03/24/19 1:11 am
Joined: Aug 2010
Posts: 327
New Hampshire, USA
David Dunfey Offline
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New Hampshire, USA
Christian,

Lovely project!

Safety wiring is well worth doing on any parts that may vibrate or hold precious fluids. One item I would safety wire is the cables. Wire them so the cables will not jump out of the adjuster otherwise you throttle may not close or your clutch will slip.

The front number plate may be legal in the UK, but in the US. it would be considered streamlining. This would put you in a different class.

I like the idea of a small tank, but in the M class there is a minimum capacity of 5 liters or 1.32 U.S. Gal. Make sure your tank is big enough.

David

Re: MAC tuning [Re: Project ROTM] #771360
04/18/19 8:50 am
04/18/19 8:50 am
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Hi David,

Thank you.

Your post has made me re-read the various rule books and yes, the tank is wayyyyy too small.



Cheers,

Christian

Re: MAC tuning [Re: Project ROTM] #771440
04/18/19 11:23 pm
04/18/19 11:23 pm
Joined: Dec 2013
Posts: 4,886
ohio, usa
kevin roberts Online content

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ohio, usa
hey christian

just to give you a sense of what size is what

i run two tanks just about 14-inches long, made from 4-inch tubes that are 1/8-inch thick. the capacity is just a few cc's over five litres


every day you do not take a chance is a day of your life that you will never get back.

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