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F1loco

Dumb question on degreeing the cam -

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So, I was putting it all back together and first locked in TDC with a piston stop.  Next up was setting the cam.  I marked the prior cam gear and chain to excess and felt like I found the perfect replacement for the new sprocket.  But the question I have is on my degree wheel - TDC, to the left is presumably BTDC and to the right is presumably ATDC.  I know the intake valve on number one is supposed to open at 17 BTDC and be fully open at 110 ATDC.  But I can't help but think (and that's probably the problem) as the engine is rotated clockwise (which I understand is the correct direction of rotation) it would make everything to the left of TDC actually "after" TDC, and everything to the right of TDC actually "before" TDC.  Reason I question all of this is with my dial indicator, I believe I have 110 nailed in - I have done multiple measurements, but both of my last readings post .050" were  221.5 and 220/2 seems pretty dialed in - EXCEPT - this is 110 the left of TDC mark, which by all reports is supposed to be BTDC, though as mentioned with the rotation of engine it seems to actually be after TDC as the engine rotates past TDC.  The shop manual diagrams seem to show the intake valve opening 17 to the left of TDC, then fully closed past BDC, at least looking at the diagram of when the I/E valves open/close.    Does this make any sense? Am I good to button it up?  

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If you are talking about the degree wheel being attached to the crank pulley, the markings to the left of TDC are ATDC, & to the right are BTDC. assuming you are looking at the front of the engine, & the top of the crank pulley.

Bob.

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Link to this site and print out the degree wheel having put in you cam and engine specs. It will give a good view of what you are after.
https://www.blocklayer.com/degree-wheel.aspx

Cheers
Peter W

PS. The second pushrod from the front is the inlet. Ask me how I know.....I chased the fully open at 110 deg ATDC using the exhaust lobe many moons ago.

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16 minutes ago, BlueTR3A-5EKT said:



PS. The second pushrod from the front is the inlet. Ask me how I know.....I chased the fully open at 110 deg ATDC using the exhaust lobe many moons ago.

Ha Ha - soul mates

 

Roger

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3 hours ago, Lebro said:

If you are talking about the degree wheel being attached to the crank pulley, the markings to the left of TDC are ATDC, & to the right are BTDC. assuming you are looking at the front of the engine, & the top of the crank pulley.

Bob.

Thanks for the affirmation guys.  The image in the shop manual was confusing me as it showed the IV opening to the left of TDC and then wide open to the right of TDC.  Think I have it pretty much dialed in between 110.25 - 110.00.  Will work on getting it all buttoned back up and hopefully running again.  

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So, I am also converting to an electric fan and skinny belt/pulley set up.  Do I reuse the oil thrower plate in conversion?  Wasn't sure about it fitting/meshing up against the new smaller pulley.  Any ideas what to torque the new crank/hub bolt too?

Edited by F1loco

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The oil thrower plate is inside the timing cover to deflect oil away from oilseal, so yes it needs to be fitted, new pulley will not affect it. Re bolt, about 60-70 lbs ft  should be plenty, whatever you choose it will be a bugger  to remove after a few years.

Chris

Edited by ChrisR-4A

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F1loco,

A good test that you have set your cam timing correctly is to use the "Equal Lift on Overlap" method.

Pistons 1 and 6 move together, but are 360 degrees out of ignition timing.      At No.1 TDC, No. 6 is also at TDC, but while No.1 is on the firing stroke (both valves closed), No.6 is in transit between the end of one four stroke cylce and the beginning of the next.      The No.6 exhaust valve is closing and the intake opening, and they overlap slightly.   More, they should be equally lifted at TDC.   (This is true for a "symmetrical" camshaft, with identical exhaust and intake cams that are symmetrical about their major axis, as are all Triumph shafts)

You can set the cam by this method.   You could check it just by eyeing it, or else by setting a wide rocker to valve stem gap (say 40thou) and then measuring the remaining gap at TDC.   Or else do it properly and use Dial Indicator Gauges.     The picture shows two such gauges, set up with dummy push rods, showing Equal Lift on Overlap.

Good luck!

JOhn

P1000707.JPG

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The one thing I still don't understand here is, when you get the cam to just be starting to open, should you subtract the tappet clearance, so that it is actually opening of the valve, or is this taken into consideration when the values for valve opening are made?

Obviously this is not true if you have equal overlap?

So if I have a cam with the inlet set to open at 35Degrees BTDC is the tappet clearance in this measurement? and this is the point that the rocker goes tight so just opening the valve?

Know doubt somebody could set my mind at rest please?

John

 

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I have always assumed that the quoted valve timing is what you get with the engine running and valve clearances set cold as dictated by cam manufacturer. Otherwise no comparison between cams could be made as all the cam does is lift the valves and basically valve lift increases power.

Chris

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One of the beauties of ELoO, I don't have to worry my pretty litle head about such things!

But I would agree with Chris - ignore valve gap as long as correctly set, its the point wherer the valve begins to open that matters.

John

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If you put a DTI on the inlet tappet and rotate the cam in the normal running direction starting from the base circle you will see the DTI not move, it will then slowly begin to rise as the clearance ramp begins, then it will suddenly rise around 3 times faster than the clearance ramp, this is the point at which the valve begins to open and is the point from which you apply the cam timing figure (ie for an SAH26 cam its 22' before top dead centre) , or the figure for whatever cam you have. 

Cheers Rob 

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Tuning Standard Triumphs 0ver 1300cc by David Vizard. ...KISS. and Nike (Just do it !).

Mick Richards

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