Winter rebuild 2 Maths help required
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Well here I am again...this time trying to dial in the cams...have made a "dropstick" to go down the No1 plughole and marked 90 degrees before TDC and after TDC (moving the degree disc until equalised ) thereby getting an accurate TDC and BTC reading...so far I'm happy that this is the most accurate way to find TDC and BDC.
But marking the dropstick at TDC, 90 degrees, BDC and 90 degrees has left me with a dilemma,why is the vertical distance between BDC to 90 degrees 44.6mm and the vertical distance between 90 degrees and TDC 33mm
Shouldn't they be the same?
P.S. Stroke is 77.6mm
John
But marking the dropstick at TDC, 90 degrees, BDC and 90 degrees has left me with a dilemma,why is the vertical distance between BDC to 90 degrees 44.6mm and the vertical distance between 90 degrees and TDC 33mm
Shouldn't they be the same?
P.S. Stroke is 77.6mm
John
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john.p.clegg - Coveted Fifth Gear
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- Joined: 21 Sep 2003
Hi John
If you draw the various triangles formed by the rod, the crank and the vertical axis up the bore you will see the triangles are a different shape from 0 degrees to 90 degrees compared to 90 to 180 degrees. The different shapes mean different amount of vertical movement over the first 90 degrees of the 180 degrees of crank rotation that forms a stroke of the piston compared to the second 90 degrees
I could solve for your rod length from your measurements but its late and I'm going to bed. Easier if you tell me your rod length and I can confirm your piston displacement measurement.
cheers
Rohan
If you draw the various triangles formed by the rod, the crank and the vertical axis up the bore you will see the triangles are a different shape from 0 degrees to 90 degrees compared to 90 to 180 degrees. The different shapes mean different amount of vertical movement over the first 90 degrees of the 180 degrees of crank rotation that forms a stroke of the piston compared to the second 90 degrees
I could solve for your rod length from your measurements but its late and I'm going to bed. Easier if you tell me your rod length and I can confirm your piston displacement measurement.
cheers
Rohan
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rgh0 - Coveted Fifth Gear
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Good night Rohan
Got me thinking (again) and yes,taking a 10cm crank and a 10 cm rod....at 90 degrees (bloody pythagoras) the vertical height will be 3.66mm not 5cm.
John
Got me thinking (again) and yes,taking a 10cm crank and a 10 cm rod....at 90 degrees (bloody pythagoras) the vertical height will be 3.66mm not 5cm.
John
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john.p.clegg - Coveted Fifth Gear
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John,
Your method for finding TDC and BDC is basically good. A refinement not mentioned in your post is to approach 90-degrees BTDC and 90-degrees ATDC from BDC. This requires turning the crank one way to reach 90 BTDC, then reversing crank rotation to reach 90 ATDC. This refinement ensures the connecting rod is in compression and clearances are consistent for both measurements.
Bill
Your method for finding TDC and BDC is basically good. A refinement not mentioned in your post is to approach 90-degrees BTDC and 90-degrees ATDC from BDC. This requires turning the crank one way to reach 90 BTDC, then reversing crank rotation to reach 90 ATDC. This refinement ensures the connecting rod is in compression and clearances are consistent for both measurements.
Bill
- bill308
- Fourth Gear
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- Joined: 27 May 2004
Bill
Correct, ( I was doing it all in the clockwise direction - as per setting camshafts - keeping the chain taut )but I wonder how much difference there would be?
will re-do tomorrow
John
Correct, ( I was doing it all in the clockwise direction - as per setting camshafts - keeping the chain taut )but I wonder how much difference there would be?
will re-do tomorrow
John
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john.p.clegg - Coveted Fifth Gear
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- Joined: 21 Sep 2003
John,
Another thing that throws you calcs out is that the gudgeon pin is not in the middle of the piston.
Cheers
John
Another thing that throws you calcs out is that the gudgeon pin is not in the middle of the piston.
Cheers
John
- elanman999
- Third Gear
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- Joined: 12 Nov 2005
John
Well you learn something new every day,or in my case plural...
Watch this space for my new toy...it's in the post.
John
Well you learn something new every day,or in my case plural...
Watch this space for my new toy...it's in the post.
John
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john.p.clegg - Coveted Fifth Gear
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- Joined: 21 Sep 2003
There is a downloadable spreadsheet at
lotus-twincam-f39/line-twin-cam-porting-article-t16194.html
that should answer many of your questions. It is almost at the end of the post. (20070702 Engine.xls).
Have fun.
David
1968 36/7988
lotus-twincam-f39/line-twin-cam-porting-article-t16194.html
that should answer many of your questions. It is almost at the end of the post. (20070702 Engine.xls).
Have fun.
David
1968 36/7988
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msd1107 - Fourth Gear
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- Joined: 24 Sep 2003
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