Author Topic: Project Return of the MAC - Vintage 350cc Velocette build  (Read 17668 times)

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Offline comet

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #15 on: January 08, 2019, 08:39:09 AM »
At least being shorter than you gut feeling you could have trimmed the pipe to suit. Better that way than trying to nail 2" back on again.  :-D

Offline thefrenchowl

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #16 on: January 08, 2019, 12:01:06 PM »
It's only a theoretical calc for exhaust length...

As a rule of thumb, one can also add:
Shorter = less torque/more power,
Longer = more torque/less power,

And bigger diameter = NO NO  :-D

Most bikes I have seen in me time are always over-carbed and over-exhausted...

Sweetest Harley Sportster I ever had was a bored/stroked (from 900 to 1200) 1959 Iron head CH with std 36mm Linkert DC carburetor, 1"1/2 high level pipes, OEM std 57/58 small valve heads and 45 deg fixed advance magneto...

See ya,

Patrick
Flat Head Forever

...What exactly are we trying to do here?...

Offline wobblywalrus

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #17 on: January 09, 2019, 10:10:17 AM »
At this stage it might be a good idea to have digital profiles made of your cams, flow test results from the cylinder head, a measured compression ratio, and rubber castings of the intake and exhaust ports.  Then, a virtual model can be made of the engine in an analysis program to figure out the answers.  The big benefits are getting the model, but more important, the things you learn about engines from reading the program user's manual and working with the example data sets that are included with the program.  This is a lot of "up front" work that saves time, money, and frustration in the long term.
 

Offline ProjectROTM

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #18 on: February 03, 2019, 09:42:25 AM »
Wobblywalrus - That is the plan and thank you for the link you sent.

I have just finished the 2nd part of my project video where I try to start the bike for the first time.

 :eek

https://www.youtube.com/watch?v=OmkGMLe9l8M

Let me know what you think.

Cheers,

Christian

Offline thefrenchowl

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #19 on: February 03, 2019, 10:44:13 AM »
 :-D

Tip to find the real TDC rather than a + or - 5 degree approximation with piston and plunger:

Fit sommat on top of bore to limit the piston travel on its upstroke, like a bar fixed across the top of the cylinder with a bolted screw sticking down in its middle. Or use a fixed version of your plunger.

Fit degree wheel and pointer in any position, then turn crank CW until the piston touches the bolt, way before TDC.

Measure the angle on the degree wheel.

Now turn the crank CWW until the piston touches again the bolt.

Measure the angle again.

Genuine TDC is right in the middle of the 2 measurements.

Move pointer and/or degree wheel so you read 0 degree at that spot.

Continue the good work...

Patrick
« Last Edit: February 03, 2019, 10:49:24 AM by thefrenchowl »
Flat Head Forever

...What exactly are we trying to do here?...

Offline ProjectROTM

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #20 on: February 05, 2019, 03:41:15 AM »
Thank you Patrick.

All advice and experience is welcomed.

Christian

Offline comet

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #21 on: February 05, 2019, 09:50:12 AM »
That's a good tip from Patrick. I have used a dial gauge in the past as well as it is more accurate than the depth gauge method.
Christian another option for your steel requirements is an online company called Metals4U. I have used them a couple of times ( no ties or relationship with this supplier) and you will find them cheaper usually than B&Q. They have a lot more choice too.
Nice job on the engine stand that came out well.

cheers

Offline wobblywalrus

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #22 on: February 05, 2019, 10:54:26 PM »
Christian, this is what heats my shed.  This is an oil radiator heater.  There are no open flames or glowing exposed electrical coils.  It works great and is a lot safer than many other methods.  It is the Italian brand De Longhi.

Offline ProjectROTM

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #23 on: February 07, 2019, 04:29:18 AM »
I am getting to the stage where I am starting to think about port flow and porting, so I dug this out from under my desk for inspiration.

If I ever make it over to Bonneville I will buy a cold beer for the first person to guess what engine the port is from. It has a ~300cc cylinder capacity.



Christian

Offline wobblywalrus

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #24 on: February 07, 2019, 09:51:43 AM »
It often helps to get flow data for the ports you have and to enter it into the computer model along with the cam profile data.  The cam lifts, port flows, and engine demands need to be compatible with each other.

Offline ProjectROTM

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #25 on: February 08, 2019, 05:38:09 PM »
Thanks Wobbly, I am going to see if I can get the head flowed so that I can baseline any porting work.

I thought I should get some practice starting the bike. Oil flow to the tank seems good. Here's a short clip for everyone that wanted to see more running. P.S. if you haven't already subscribed to my channel, please do.

https://www.youtube.com/watch?v=929tKg-4UYs

Christian

Offline wobblywalrus

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #26 on: February 09, 2019, 12:57:05 AM »
A problem with old bikes is that we do not know what we are working with unless measurements are taken and we look at them analytically.  Years ago I owned a BSA Spitfire.  The bike had bigger intake valves installed and the ports were flowed in the factory.  Of course, I enlarged them and the bike ran worse.  Same with a Matchless G80CSR scrambler.  Someone, maybe Jerry Branch, ported the head.  I "improved" the port size without knowing they were plenty big to start with.  The bike ran terrible except at very high rpm after I did this.

Typical flow data is for the valve lift at .025 inch increments with just the head.  Then, with the head and manifold and carb.  Then with the head, manifold, carb, and filter.  Usually flows are measured at increments up to .5 inch valve lift.  Usual results are three flow vs lift curves for the inlet and one for the exhaust.  The fellow that flow tests my exhaust port puts a short stub pipe on the head to simulate the exhaust system.     

Offline ProjectROTM

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #27 on: February 19, 2019, 07:37:37 AM »
No body guessed what the port was from, but i will show you anyway  :-D

It is the intake port from this, a development flow log for a V8 F1 engine. Small cylinder capacity, but big bore.



Also, I have finally worked out how to post pictures onto the forum!!!!!!

Cheers,

Christian

Offline comet

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #28 on: February 19, 2019, 09:57:23 AM »
I do love the sound of an old single. You cant beat it.

Offline ProjectROTM

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Re: Project Return of the MAC - Vintage 350cc Velocette build
« Reply #29 on: February 20, 2019, 03:28:26 PM »
The development flow log is from this engine...

https://youtu.be/X3mFKjKosbI

https://www.youtube.com/watch?v=X3mFKjKosbI&t=28s

I promise the next post will be fully back on topic!!!

Cheers,

Christian