Camshaft deegreeing question
Discussion
carlt5 said:
Simple question sort of relating to this topic ,as I want to measure actual valve timing figures for some unknown cams I have.
As a generalisation , when a tappet/follower clearance is set ,e.g. 10thou" cold , how much of that clearance reduces when an engine is at running temp.- e.g. does it close to 2thou"clearance ?
i.e. if I want to measure actual valve opening point , relative to crank rotation, on a cold engine what should the tappet clearance be set at
cheers
carl
If you want to measure the duration at 1.00mm lift, set the clearance to the correct size and turn the engine until you get 1mm lift on the opening event. Make a note of the crank angle and then turn through the full lift of the cam until you get back to 1mm lift on the closing envent. Again, make a note of the crank angl, then do the sums.As a generalisation , when a tappet/follower clearance is set ,e.g. 10thou" cold , how much of that clearance reduces when an engine is at running temp.- e.g. does it close to 2thou"clearance ?
i.e. if I want to measure actual valve opening point , relative to crank rotation, on a cold engine what should the tappet clearance be set at
cheers
carl
I think you are over complicating this.
The confusion stems from the fact that manufacturers (of cars and cams) DO NOT all use the same rules as each other, there are only two ways you can be sure you are correctly comparing cam A with cam B for duration:
1. Be 100% sure how the engine manufacturer measured the cam (i.e at what clearance) and do yours the same.
2. Measure both cams at your (presumably factory recommended) clearances and compare.
Take this Catcam sheet for instance: http://www.catcams.co.uk/acatalog/Ford_YB_Cosworth...
Duration is with clearance (i.e measured at the valve), but they don't say what clearance.
Max lift of cam and at TDC is quoted with 0 clearance (i.e it is measured at the cam, not the valve)
I have found that Cat will list what the clearance they took the duration at on the sheet you get when you've bought the cams, it quite often isn't the engine manufacturers clearance!
I work mainly on Lancias Lampredi designed twin-cams, on paper the factories durations look very short until you look closer and realise they measured them at .8mm clearance, the engines never ran .8 clearance.....
The Meercans don't measure duration at 1mm, it's at 1.27.
For the novice or man in the garden shed this makes things very difficult and I'm afraid it is only experience, knowledge and computer programs/software which can help here.
There is sometimes a bit of 'fudging' figures because you know what to expect, from very little to shifting the power up and down the rev range etc. Quite often .27 of a mm can't be felt or seen on a dyno, so you have to ask yourself if you need to work to that kind of tolerance and will there be a loss or a gain in power by doing so....
1. Be 100% sure how the engine manufacturer measured the cam (i.e at what clearance) and do yours the same.
2. Measure both cams at your (presumably factory recommended) clearances and compare.
Take this Catcam sheet for instance: http://www.catcams.co.uk/acatalog/Ford_YB_Cosworth...
Duration is with clearance (i.e measured at the valve), but they don't say what clearance.
Max lift of cam and at TDC is quoted with 0 clearance (i.e it is measured at the cam, not the valve)
I have found that Cat will list what the clearance they took the duration at on the sheet you get when you've bought the cams, it quite often isn't the engine manufacturers clearance!
I work mainly on Lancias Lampredi designed twin-cams, on paper the factories durations look very short until you look closer and realise they measured them at .8mm clearance, the engines never ran .8 clearance.....
The Meercans don't measure duration at 1mm, it's at 1.27.
For the novice or man in the garden shed this makes things very difficult and I'm afraid it is only experience, knowledge and computer programs/software which can help here.
There is sometimes a bit of 'fudging' figures because you know what to expect, from very little to shifting the power up and down the rev range etc. Quite often .27 of a mm can't be felt or seen on a dyno, so you have to ask yourself if you need to work to that kind of tolerance and will there be a loss or a gain in power by doing so....
Iv finally worked out how to do it all but you need to know your peak valve lift in degrees for your engine. For example my engine is 108 degrees for exhaust valve fully open. And 122 degrees for inlet fully open.regardless of what cams are used. The next thing you need to do is using a dial test indicator (mag base and clock) measure your duration and write it down. For example my valve clearances are 0.25mm and I want to measure at 1mm so I start measuring at 1.25mm.
Say it's 230 degrees.
So now you have peak lift and degrees what next?
230/2=115 degrees for my engine the exhaust is 108 peak lift.
FOR EXHAUST ALWAYS SUBTRACT THE CLOSING VALUE.
But we don't know this yet. But we have 115 and 108 the difference is 7. So your closing value is 7 degrees after TDC
to find the opening value it's 180+7=187
230-187=43 degrees open before BDC.
To check it's right add the two opening and closing points together plus 180.
43+7+180= 230
For inlet i know 122 is peak valve lift and measured degrees is 230.
230/2=115
FOR INLET MINUS THE OPENING FIGURE
115 minus what gives us 122?
It's -7 two minus makes a positive so basically the inlet is opening and exhaust are closing at the same point. Iv checked these against known cam spec sheet and it all ties in with same values.which can be found here http://www.catcams.com/products/camshafts/datashee...
Try another one because the minus thing is confusing.
Measured degrees 251 for inlet
251/2=126
126- inlet figure? what gives us 122
Inlet opens 4 degrees
180+4
251-184=67 degrees closing
To check 67+4+180=251 :-)
See here http://www.catcams.com/products/camshafts/datashee...
Say it's 230 degrees.
So now you have peak lift and degrees what next?
230/2=115 degrees for my engine the exhaust is 108 peak lift.
FOR EXHAUST ALWAYS SUBTRACT THE CLOSING VALUE.
But we don't know this yet. But we have 115 and 108 the difference is 7. So your closing value is 7 degrees after TDC
to find the opening value it's 180+7=187
230-187=43 degrees open before BDC.
To check it's right add the two opening and closing points together plus 180.
43+7+180= 230
For inlet i know 122 is peak valve lift and measured degrees is 230.
230/2=115
FOR INLET MINUS THE OPENING FIGURE
115 minus what gives us 122?
It's -7 two minus makes a positive so basically the inlet is opening and exhaust are closing at the same point. Iv checked these against known cam spec sheet and it all ties in with same values.which can be found here http://www.catcams.com/products/camshafts/datashee...
Try another one because the minus thing is confusing.
Measured degrees 251 for inlet
251/2=126
126- inlet figure? what gives us 122
Inlet opens 4 degrees
180+4
251-184=67 degrees closing
To check 67+4+180=251 :-)
See here http://www.catcams.com/products/camshafts/datashee...
Christ you're making a f**king meal of this. 1mm lift at the valve is 1mm lift at the valve. End of! The valve clearance has already been taken up before the valve starts to move and is therefore irrelevant. If you were trying to measure directly off the cam lobe then 1mm at the valve would be 1mm plus the valve clearance at the lobe but you aren't!
delcbr said:
Stuff
You need to get yourself set up with some dial gauges, TDC sensor, engine stand, timing wheel, wire pointer etc and get busy.When you've spent a few hours with it a lot will become clear.
If it's an alloy head your mag stand will be of no use unless you bolt a rigid steel plate on, it may be of some help if you mention what engine this is too...
BMW M3 3.0 it has alloy head.
Yes variable cam timing on inlet only 122-80 degrees.
But set the cams up retarded.
Iv got the tools but not the knowledge until now. I used the BMW cam alignment tools to set up the cams because I don't have a timing sheet. But now i can measure the duration and calculate the opening and closing points and set it up accordingly.
Yes variable cam timing on inlet only 122-80 degrees.
But set the cams up retarded.
Iv got the tools but not the knowledge until now. I used the BMW cam alignment tools to set up the cams because I don't have a timing sheet. But now i can measure the duration and calculate the opening and closing points and set it up accordingly.
I've just been messing about measuring some unknown cams I've been given for the Ford 1172 side valve
didn't realise that variations in tappet/follower clearance made such a difference in the valve opening and closing timings [2thou" was 10deg crank position]
Does this equate to any significant noticeable performance change in real testing - say using 4thou" less clearance
didn't realise that variations in tappet/follower clearance made such a difference in the valve opening and closing timings [2thou" was 10deg crank position]
Does this equate to any significant noticeable performance change in real testing - say using 4thou" less clearance
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