First 4 Stroke First V twin.

[Steamchick]

Thanks Mechanicboy, I had not considered the "late" closure of the inlet valve would also discharge some mixture if the valve is open after BDC of the intake stroke. A new condition for me, but quite conceivable with a new engine where we do not know all the details of the actual valve timing. My only experience of this was with engines that had large overlap and when running at "slow" speeds the exhaust back-pressure caused some mixture to be expelled when the gases came back through the inlet valve upon opening of the inlet while the exhaust was still open. - In this mode, the racing motorcycles had no problem when at higher revs as the overlap enhanced performance and did not spit back.
K2

 

[Mechanicboy]

This is normal when you get a little pulsating pressure in the carburettor during idling due to overlap, but do not throw out the mixture of the carburettor at higher speeds. It is the gas velocity that must be high enough until the mixture is not forced out of the cylinder after BDC before the gas velocity is reduced enough until the intake valve closes in time so that the cylinder has enough mixture to compress and burn efficiently. It is due to the mass of the mixture under high gas velocity that is strong enough to fill the cylinder before the piston forces the mixture out of the cylinder just after BDC.

As a starting point, the intake valve opens about 20-25 degrees before TDC and closes about 30-35 after BDC and the exhaust valve opens about 35-40 before BDC and closes about after 10-15 BTC. This is just a guide to making the camshaft with such timing. Overlap works best with longer exhaust pipes instead of directly out of the cylinder head without exhaust pipes due to the vacuum effect caused by the mass of exhaust at high speed.

 

[c_mario]

HI,
I don't really understand all the cam timing stuff I only went by the drawings where it states the following of the cam lobes in relation to each other.
Exhaust Cam Cylinder 1 0 Degrees, Inlet Cam Cylinder 1 114 Degrees
Exhaust cam Cylinder 2 135 Degrees, Inlet Cam Cylinder 2 249 Degrees

Base Radius 4.4 mm. Flank Radius 22 mm. Nose Radius 2.4 mm. Valve Lift 2 mm.

Then the instructions say to make the timing so that when cylinder 1 is at Top Dead centre align the cam so that inlet and exhaust valves are open the same amount. I guess that is the point at which there is maximum overlap.

 

[Mechanicboy]

Exhaust Cam Cylinder 1 0 Degrees, Inlet Cam Cylinder 1 114 Degrees
Exhaust cam Cylinder 2 135 Degrees, Inlet Cam Cylinder 2 249 Degrees

???

Do you have the plan of the camshaft and camlobe in degree to show?

 

[Ghosty]

Mechanicboy, they have very limited info on the cam angles, It has taken me 6 different cam grinds to get close to getting one to run correctly, and I am still working on it

Cheers
Andrew

 

[Mechanicboy]

Yes, I can't see where is the angle of the camlobe on the drawings as you showed. Hence it's so difficult to make the correct camlobe without degree of camlobe to open/shut the valve in right timing.

See at this picture as you can see this lift periode is 120 degree on both camlobe, this is divided by 2 where the crank shaft rotation will be 240 degree.
And the overlap is 7,5 + 10 = 17,5 degree x 2 is 35 degree.

The intake is open 15 degree before TDC and closed 45 degree after BDC.
The exhaust is open 40 degree before BDC and closed 20 degree after TDC.
This is just a guide to understand timing.
(Timing is near same as I can see in the Peugeot TU3/TU5 engine who I am working as Peugeot car mechanic.)

Learn out how to create the cam on lathe here.

See this movie..

 

[c_mario]

Hi,
I plugged the values given in the drawing into a excel chart that gave values for cutting on a mill with rotary table. Cuts every 3 Degrees , 120cuts per Cam. I did see the above movie but didn't quite understand it so I used the Method below following the cutting parameters calculated by the excel chart.

 

[Mechanicboy]

You can use Bob Shore's method of milling the camshaft: Mill the first flank and then turn slow the indexing head 240 degrees while continuing to mill the base circle until you stop 240 degrees and mill the last flank. To turn 240 degrees using the indexing head you need 18 holes disc. 26 turns and 18 holes in the 27 hole disc provide a 240 degree angle. Carefully remove the milling marks with a needle file and honing stone. Round a little at the top of the cam.

 

[minh-thanh]

Hi !

they have very limited info on the cam angles, It has taken me 6 different cam grinds to get close to getting one to run correctly, and I am still working on it

Cheers
Andrew

Why do you have to do 6 camshafts ?
Has the design of this engine been proven or not ?

 

[Mechanicboy]

Hi !


Why do you have to do 6 camshafts ?
Has the design of this engine been proven or not ?

Minh-Thanh..

The main problem: Where is the center of point to set radius 11 mm to create cam profile. 4 mm distance is not easy to set point to create camlobe. And where is the whole angle on the camlobe? See at the drawings who are marked with green. There is not timing diagram to show. It make more difficult to make the cam without all complete measures as you can find in the older drawings to example Westbury's model engine. Also the German engine designer done the drawings incomplete.

 

[c_mario]

Hi,
I'm just a novice I used an excel workbook that someone created and fed it values and it came up with a milling table.
This is the first page of the workbook all values converted to inch's from the values from the plans. I thought it gave enough values to do the calculations.
Base Radius 4.4 mm. Flank Radius 22 mm. Lift 2 mm . To get Working angle I plugged in values till the calculated Nose Radius came to 2.4 mm as shown in the plans.

 

[Mechanicboy]

c_mario

131 degree are a bit too much, it means 131 x 2 = 262 degree in valve timing when I am thinking the fuel mix is blowing out of carburettor.

For a normal high speed engine is set to 250 degree for intake and 255 degree for exhaust and the overlap is 30 degree with 10 degree before TDC for intake and 20 degree after TDC for exhaust. How to calculate angle of camlobe: Valve timing : 2 = angle of cam lobe.

Then you do it this if you want 262 degree in valve timing...

360 degree - 131 degree camlobe = 229 degree from flank to flank when milling the base circle.

To turn 229 degrees using the indexing head you need 18 holes disc. 25 turns and 4 holes in the 18 hole disc provide a 240 degree angle. Carefully remove the milling marks with a needle file and honing stone. Round a little at the top of the cam.
(Indexing head with 1:40: Degree : 9 degree = turns-counts of hole/hole in plate.)

 

[c_mario]

Hi Mechanicboy.
Ok I think I see your point. I did ask the designer for comment but have not received a response yet. So if I set the working angle to 125 degrees , the nose radius calculates to around 1.9 mm and the cam shape changes as seen in the diagram below.
So the valves will stay open for a shorter period of time and there would be less overlap if I kept everything else the same as previous.

 

[Mechanicboy]

It looks good, .. you have to try it until you see that not a lot of fuelmix is spit out of the carburetor since it is not economical when the unused fuel is throwed out of the engine.

 

[awake]

For a normal high speed engine is set to 250 degree for intake and 255 degree for exhaust and the overlap is 30 degree with 10 degree before BTC for intake and 20 degree after BTC for exhaust. How to calculate angle of camlobe: Valve timing : 2 = angle of cam lobe.

Mechanicboy, in several of your posts you have mentioned "before BTC" and "after BTC." I thought "BTC" meant before top center, so "after BTC" seems self-contradictory - ??? This may just be my ignorance showing, but wanted to check in case this is confusing for anyone else.

 

[Mechanicboy]

Mechanicboy, in several of your posts you have mentioned "before BTC" and "after BTC." I thought "BTC" meant before top center, so "after BTC" seems self-contradictory - ??? This may just be my ignorance showing, but wanted to check in case this is confusing for anyone else.

Mis-wrote the text.. 10 degree before TDC begins intake valve to open and 20 degree after TDC begins exhaust to close.

 

[awake]

Mis-wrote the text.. 10 degree before TDC begins intake valve to open and 20 degree after TDC begins exhaust to close.

I'm still confused by "BTC." What does that abbreviation stand for?

 

[Mechanicboy]

I'm still confused by "BTC." What does that abbreviation stand for?

Exactly, I messed with the letter in the order, .. It should be TDC = Top dead center I has edited to correct text..

 

[awake]

Jens, thanks so much. I was afraid I had gotten mixed up. Valve timing is still rather mysterious to me ... !

 

[Steamchick]

Thanks all for clarifying what can appear to some (I.E. me!) to be somewhere between "rocket science" and "black art". I have changed cams and followers of various profiles on 500cc Triumph engines, to appreciate the different performances they produce, but otherwise have never thought about cam geometry.
Mechanic boy, I especially liked your valve diagram. Thanks!
K2