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Author Topic: Project Return of the MAC - Vintage 350cc Velocette build  (Read 1752 times)
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comet
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« 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.  grin
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thefrenchowl
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« 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  grin

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
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Flat Head Forever

...What exactly are we trying to do here?...
wobblywalrus
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« 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.
 
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ProjectROTM
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« 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



Let me know what you think.

Cheers,

Christian
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thefrenchowl
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« Reply #19 on: February 03, 2019, 10:44:13 AM »

 grin

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 » Logged

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ProjectROTM
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« Reply #20 on: February 05, 2019, 03:41:15 AM »

Thank you Patrick.

All advice and experience is welcomed.

Christian
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comet
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« 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
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wobblywalrus
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« 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.


* De Longhi heater.JPG (204.74 KB, 724x1024 - viewed 14 times.)
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ProjectROTM
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« 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


* Port1 (2).jpg (449.29 KB, 1512x2015 - viewed 42 times.)
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wobblywalrus
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« 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.
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ProjectROTM
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« 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.



Christian
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wobblywalrus
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« 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.     
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