Need some professional advice on cams

[Trevor]

Originally Posted by TomsSVX

maybe it would be best for someone that has a head off a motor to do the measurements. This way the lifter can be taken into account? What would Bill think about it measuring my old heads?? Bill??

Tom,

Tom,

The measurements should not be taken with the head off. All must be in place and exactly operational as normal. I have advised the correct way to do it. The actual relationship with crankshaft position must be positively varified when all is set up as running. Lift is a separate aspect in the equation.

I see that Harvey's instructions have been suggested. In the light of his previous posts, it would be interesting to see those instructions. If decissions are going to be based on measurements made using that which could be suspect, I will have no further confidence in the project.

Sincerely, Trevor.

[SVXRide]

Okay, here you go....





-Bill (yeah, I really don't have these cams in my engine....honest!)

[SVXRide]

Trevor,
In response to your request, here's what Harvey PM'ed me:

Checking valve timing, and lobe center.

This is the method I would use to check the valve timing and find the inlet lobe center.
I use a plastic degree wheel stuck, to the harmonic balancer, with double sided tape, with the TDC marks aligned. Set up a wire pointer on one of the bolts on the front of the engine, so that it is in line with the 0 degrees on the degree disc.
Zeroing the degree disc to the crank.
Set up a dial indicator through the plug hole, and zero it while the piston is at TDC. Rotate the engine( always turning the engine forwards,NEVER TURN IT BACKWARDS) till the dial ind. shows the piston has dropped 0.050". read the degrees the crank has turned pass TDC. Say it is 12*. Turn the engine over till the piston is 0.050" from the TDC. Read the degrees, say it is 8*, that means that the wire pointer is too far to the 12* side, so we half the difference 4*, and move the wire pointer 2* to the 8* side, so that the pointer is aligned with 10* BTDC. This zeros the degree wheel to the crank, it will now read the same 10* at 0.050" before and after TDC.

Measuring the valve timing.
Set up the dial indicator on the top of the valve follower, zero the needle. There is two different ways to show duration figures, the US way is to start the measurement at 0.050" lift, and end 0.050" from the fully closed position. The other which everyone else uses, is from seat to seat. Turn the engine till the dial shows the first movement, of the valve opening, read off the degrees BTDC. (This is the start of the seat to seat duration.) Keep turning till the follower has moved 0.050", read off the degrees, (this is the start of the US duration). Turn the engine over till the valve is 0.050" from closing, (US closing point), keep turning till the valve has stopped. (end of the s to s duration)

The book quotes the timing to be ;Inlet 2* BTDC, 54* ABDC 236* Duration. Exhaust 55* BBDC, 9* ATDC. 244* Duration.

Finding the lobe center.
Turn the engine till the valve is fully open, zero the dial needle. Turn the engine till the dial shows 0.050" from fully open, read the degrees, keep turning till the valve has closed 0.050", read the degrees. Add the two degree readings together divide by two. This is the inlet lobe center. Worked out from the timing in the book, this is 116* ATDC.

If you can find what the factory lobe center is, and what the new cam duration and lobe center is. We will know where we stand.

-Bill (aka "Fountain of Cam Knowledge" )

[Trevor]

Originally Posted by SVXRide

Trevor,
In response to your request, here's what Harvey PM'ed me:

Checking valve timing, and lobe center.

This is the method I would use to check the valve timing and find the inlet lobe center.
I use a plastic degree wheel stuck, to the harmonic balancer, with double sided tape, with the TDC marks aligned. Set up a wire pointer on one of the bolts on the front of the engine, so that it is in line with the 0 degrees on the degree disc.
Zeroing the degree disc to the crank.
-----------------------------------

AGREED, Provided "Zeroing the disc to the crank" clearly means at TDC.

The following in appears to be made up from words lifted from a US publication, which is fair enough.
----------------------------------

Set up a dial indicator through the plug hole, and zero it while the piston is at TDC. Rotate the engine( always turning the engine forwards,NEVER TURN IT BACKWARDS) till the dial ind. shows the piston has dropped 0.050". read the degrees the crank has turned pass TDC. Say it is 12*. Turn the engine over till the piston is 0.050" from the TDC. Read the degrees, say it is 8*, that means that the wire pointer is too far to the 12* side, so we half the difference 4*, and move the wire pointer 2* to the 8* side, so that the pointer is aligned with 10* BTDC. This zeros the degree wheel to the crank, it will now read the same 10* at 0.050" before and after TDC.
----------------------------------

AGREED AS A WAY OF CONFIRMING TDC, if this can not be established from reliable marks. This method can be simplified by using a probe and educated feel, to establish that the piston is rockiong over TDC, if a dial gauge is not available. The "never turn the engine backwards", suggests the possibility of excessive big end clearance, which should become obvious while rocking the crank shaft. However this instruction should be carried forward regarding cam measurements, as here tolerances in the camshaft drive must be taken into account.
--------------------------------

Measuring the valve timing.
Set up the dial indicator on the top of the valve follower, zero the needle. There is two different ways to show duration figures, the US way is to start the measurement at 0.050" lift, and end 0.050" from the fully closed position. The other which everyone else uses, is from seat to seat. Turn the engine till the dial shows the first movement, of the valve opening, read off the degrees BTDC. (This is the start of the seat to seat duration.) Keep turning till the follower has moved 0.050", read off the degrees, (this is the start of the US duration). Turn the engine over till the valve is 0.050" from closing, (US closing point), keep turning till the valve has stopped. (end of the s to s duration)

The book quotes the timing to be ;Inlet 2* BTDC, 54* ABDC 236* Duration. Exhaust 55* BBDC, 9* ATDC. 244* Duration.
---------------------------

AGREED.

Finding the lobe center.
Turn the engine till the valve is fully open, zero the dial needle. Turn the engine till the dial shows 0.050" from fully open, read the degrees, keep turning till the valve has closed 0.050", read the degrees. Add the two degree readings together divide by two. This is the inlet lobe center.
-------------------------------

READING THE PROTRACTOR when the valve is established to be at full lift will give the exact lobe centre in practical terms, without any calculations. But do not rock the shaft without thought, unless absolutely no play is present in the cam drive.

Although it is desirable to use a dial gauge in making all of these measurements, the eye and feel can be very accurate if used sensibly .
------------------------------

If you can find what the factory lobe center is, and what the new cam duration and lobe center is. We will know where we stand.
-----------------------------
AGREED --- N.B. we already know the factory lobe centre if we accept published figure, but a check would be worthwhile and could also varify other mearsurement methods have been reliable

-Bill (aka "Fountain of Cam Knowledge" )

Please be sure that my intention is not to be smart by adding the above comments and that most of all I simply wish to assist.

[Trevor]

Originally Posted by SVXRide

Okay, here you go....

-Bill (yeah, I really don't have these cams in my engine....honest!)

Regarding the timing sheets -- please confim that the first sheet covers the stock cams and the second the modified cams as were supplied, or advise if otherwise.

Thanks, Trevor.

[SVXRide]

Originally Posted by Trevor

Regarding the timing sheets -- please confim that the first sheet covers the stock cams and the second the modified cams as were supplied, or advise if otherwise.

Thanks, Trevor.

Trevor,
The top part of the sheet is supposed to be the specs of the stock intake cams, the bottom the "modified" intake cams.
-Bill

[SVXRide]

Trevor,

Could you take a look at this thread to see what you think, relative to how it fits in with the info in this thread?

http://www.subaru-svx.net/forum/show...ight=Cam+Lobes

-Bill

[Trevor]

Originally Posted by SVXRide

Trevor,

Could you take a look at this thread to see what you think, relative to how it fits in with the info in this thread?

http://www.subaru-svx.net/forum/show...ight=Cam+Lobes

-Bill

A good deal of investigation appears to have taken place but I can not understand why all of the measurements and specifications do not relate the effective valve openings to crankshaft position i.e. BTDC and ATDC. The duration alone does not give the required picture. Until this is established all is in the dark.

There appears to have been some emphasis towards valve lift, although this may have been so as to be able to accommodate existing cam profiles. There is also reference to reducing valve seat width which will effect seat wear. The SVX has a very large valve area and therefore both of these modifications are not as relevant as they were before the four valve era. Increased valve lift carries with it disadvantages in respect of greatly increased mechanical loading. In both of these areas anticipated improvement must be carefully weighed against the negative effects. My understanding is that you are not intent on building race engines, which will be pulled down and refreshed at short intervals.

Based on the limited information you had on hand it would appear that you went with the right lobe shape as a starter, but still have not established where this sits in relation to TDC, which is a VITAL issue. The very essence of valve timing revolves around piston travel and position, relative to valve position and I can not understand how this so far appears have been ignored.

I note that Harvey has brought aspects of the inlet tract into the discussion, which does no more than confuse the issue. I agree that this and valve timing are related, but each is independent of the other and with due consideration can be adjusted individually.

[Trevor]

Originally Posted by SVXRide

Trevor,
The top part of the sheet is supposed to be the specs of the stock intake cams, the bottom the "modified" intake cams.
-Bill

Bill , I can not relate the figures recorded for the stock cams, with the figures published by Subaru. e.g.

Intake opening: -27 BTDC (Very strange figure). Subaru's figure: 2* BTDC (Logical).

Intake closing; 33.8 ABDC. Subaru's figure: 54 ABDC.

Duration: 186.9 crank degrees. Subauru's figure: (Calculated) 236*.

Lobe centre: 120.6* ATDC. Subaru's figure: (Calculated) 120*).
N.B. This figure is within tolerance.

How can one have confidence in the figures for the modified cams? Your own measurements become even more essential!

Cheers, Trevor.

[Trevor]

Originally Posted by Trevor

Bill , I can not relate the figures recorded for the stock cams, with the figures published by Subaru. e.g.

Intake opening: -27 BTDC (Very strange figure). Subaru's figure: 2* BTDC (Logical).

Intake closing; 33.8 ABDC. Subaru's figure: 54 ABDC.

Duration: 186.9 crank degrees. Subauru's figure: (Calculated) 236*.

Lobe centre: 120.6* ATDC. Subaru's figure: (Calculated) 120*).
N.B. This figure is within tolerance.

How can one have confidence in the figures for the modified cams? Your own measurements become even more essential!

Cheers, Trevor.

After giving the matter further thought overnight I think I may have come up with an answer regarding the variations in figures. I think measurements as above, have been taken using a point contact with the cam lobe rather than a flat surface as applies in respect of the engine. The valves in SVX engine obviously are operated by contact with flat followers rather than sharply radiussed rockers and this is a very important aspect to be taken into account. With this in mind the figure I found to be strange i.e. -27, could mean, point 27 and I will look into all this again.

This brings up the important point that when profiles as such, are compared one against the other, the associated mechanical arrangements must be taken into account. It is therefore best to use the engine manufactures valve timing figures.

All this probably came to mind as a result of early experience. Over Fifty years ago, when I built my first car to go motor racing on a very, very low budget, I studied the effects of valve timing and came up with an idea based on the preceding facts. The engine I was using had a single over head cam operating inclined valves, one each side, via rockers having contact surfaces with a sharp radius. I built these up with hard welding, ground them flat and the result will be obvious. Strangely I have never read of any one else using this cheap but effective method.

[Trevor]

After further thought and calculations, it would appear the the figures prefixed with "-" i.e. a negative sign, should be taken as indicating in effect ATDC, not BTDC. If this, as well as point contact measurement is accepted, things fall more or less into place. Please read this in conjuction with my previous posts.

One can of worms, to be sorted out only by means of actual readings in respect of the modified cams. These figures I await with great interest.

[oab_au]

The figures quoted in Bills slips are US timing, taken at 0.050" lift as I stated in the PM that I sent him, and has been posted.

Harvey.

[Trevor]

Originally Posted by oab_au

The figures quoted in Bills slips are US timing, taken at 0.050" lift as I stated in the PM that I sent him, and has been posted.

Harvey.

If that is so, you will be able to correlate this fact with the figures quoted in the sheets and Subaru's specifications and exactly explain the reason for a discrepancy in numerical terms. These figures will be awaited with interest.

I can see why a constant degree of lift was used in the instructions which you provided, so as to elliminate possible error through backlash, but I had presumed that these instructions were specifically intended to establish only the lobe centre.

Can you please advise how what you state, can be confirmed as a universal system used in US. This is certainly very important in relation to the exercise underway. It would appear to be a very difficult system to directly convert to that which is normal, considering the variables involved. Can you suggest a conversion factor?

[oab_au]

Originally Posted by Trevor

If that is so, you will be able to correlate this fact with the figures quoted in the sheets and Subaru's specifications and exactly explain the reason for a discrepancy in numerical terms. These figures will be awaited with interest.

I can see why a constant degree of lift was used in the instructions which you provided, so as to elliminate possible error through backlash, but I had presumed that these instructions were specifically intended to establish only the lobe centre.

Can you please advise how what you state, can be confirmed as a universal system used in US. This is certainly very important in relation to the exercise underway. It would appear to be a very difficult system to directly convert to that which is normal, considering the variables involved. Can you suggest a conversion factor?

1. You just have to take both sets of figures as fact, for the two measurements. Subaru's are "seat to seat", the US timings are at .050" lift.

2. If you are referring to the way the lobe center is found. It is not to eliminate backlash in the drive train, but the lack of valve movement over the fully open position, that may take more than 15* degrees, we need it more accurate than that.

3. I don't know if it is universal,. but you will have trouble finding a seat to seat measurement in any cam grinders settings. The small ends of the cam opening, don't have a big effect on the results, it is mainly to do with the ramps that open and close the valve. As there are many different types of followers, direct acting flat solid or hydraulic and roller, symmetrical profiles. And the asymmetrical profile for lever finger, rocker types of followers.
So they just leave them out and use the business end of the cam, from 0.050" on.

Harvey.

[Trevor]

Originally Posted by oab_au

1. You just have to take both sets of figures as fact, for the two measurements. Subaru's are "seat to seat", the US timings are at .050" lift.


******** I do not have to take anything as fact, if it is not true. Please give me the figures as requested.

******** "US timings". If there is such a thing as US timing, this needs to known as it becomes a vital and necessary contingency.


2. If you are referring to the way the lobe center is found. It is not to eliminate backlash in the drive train, but the lack of valve movement over the fully open position, that may take more than 15* degrees, we need it more accurate than that.


*******I am not referring to any such event! Your words have no meaning. What has the alleged - "the lack of valve movement over the fully open position, that may take more than 15* degrees" - to do with the issue of timing measurements taken from the start and end of the lift.
What is more you are stating that the cams are in fact flat over 15 degrees at full lift, or nealy flat or whatever. Is this some sort of claim that full lift can not be easily established at better than 7.5 degrees? In any event again what has this got to do with an elapsed period from the start to the end of lift.

3. I don't know if it is universal, but you will have trouble finding a seat to seat measurement in any cam grinders settings. The small ends of the cam opening, don't have a big effect on the results, it is mainly to do with the ramps that open and close the valve. As there are many different types of followers, direct acting flat solid or hydraulic and roller, symmetrical profiles. And the asymmetrical profile for lever finger, rocker types of followers. So they just leave them out and use the business end of the cam, from 0.050" on.


****** Your original statement was definitive. There is a universally accepted method of measuring valve timing and I, others and Subaru use it. I note that you have learned a little from this thread, relative to cam followers and their effect.

It is interesting, that you now confirm exacly what I have suggested, i.e. that measurements have been taken by the grinders at a point of contact. This being the essence of what I have suggested as a reason for the discrepancies. Your theory relies on the existance of a special US form of measurement.

N.B. Is there or is there not a US system involving a 0.050" included measurement, those involved with this thread, need to know. Is such a standard system in use, recorded, if so where?

Your reply will be awaited with interest and concern in respect of others involved in this issue. *<)

P. S. Harvey, there are now accurate answers posted. I appologies for my rather curt message, but I continue to not agree with the logic and some statements in your proposal. What has now been properly set out indicates that my theory although logical was apparently wrong and I accept that yours was basically correct.