TC valve timing

PostPost by: rdssdi » Fri Apr 26, 2013 11:46 pm

I am assembling my TC engine. All looked fine but for carbon on the pistons and combustion chambers. All is now clean and the head has been reattached.

The proper valve timing requires two "dots" on the gear sprokets to be positioned in line with the front case and facing each other. When assembled mine do not align evenly. One dot (exhaust) when aligned with the case leaves the other dot slightly below that level. Short of offset dowels what can I do? These are now sprockets and chain.

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PostPost by: rdssdi » Fri Apr 26, 2013 11:57 pm

Sorry been a long day substitute "new" for "now". Sorry
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PostPost by: StressCraxx » Sat Apr 27, 2013 3:40 am

Ahh, an almost Zen like experience it is, degreeing cams. Getting the marks to line up is good, as long as the head has not been resurfaced, the chain is new. Either or both conditions may cause the marks to be in the position you have now. One sprocket should be marked "EX" and should be on the exhaust cam. When they built the engines on the production line, simply getting the marks to line up within tolerance was sufficient. Offset dowels are how the cams are timed to the desired value at the crank. There is a performance and driveablity benefit to timing correctly.

Cam timing is done with a degree wheel on the crank pulley, a pointer for the degree wheel to point to 0 TDC.

A clamp on dial indicator is needed to establish TDC and to determine the valve timing events for your cam.

The process isn't too difficult, but its really helpful to have someone walk you through if you haven't done it before. It does take some time and patience. The cam timing specs are in the manual for the std, S/E and Sprint cams. If you have aftermarket cams, the instructions/specs that came with them should be used.

The key elements are:

You want the intake valve to open when the crank/piston is ready to pull the air/fuel mix in at a specific position.
You want the exhaust valve to open when the crank/piston is at the right position to push the exhaust out the chamber.

In my case I had to advance my intake cam 3 deg because the head had been resurfaced. The exhaust was less than 1 degree out. If you search on the web, there are several videos explaining the procedure. The explanation below from Isky is really good, particularly for establishing TDC accurately.

http://www.iskycams.com/degreeing.php
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PostPost by: rdssdi » Sat Apr 27, 2013 8:02 pm

thanks. I will read through the info you have provided. Its always something. I will post the results. I do not have the cam info. The cams were supplied by the engine rebuilder Marcovicci and Wenz. I believe they are SE spec.

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PostPost by: CBUEB1771 » Sun Apr 28, 2013 3:09 pm

Marcovicci Wenz is still in business. I would start with them to get the correct lobe center values for your cams.
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PostPost by: billwill » Sun Apr 28, 2013 3:41 pm

It is fairly normal that the two dots do not line up exactly, which is why I always advise taking a photo of the cam sprockets, as soon as you have the cover off and before you dismantle the chain etc. Then you can see that you have put them back in the right place later. Only if you want to squeeze the absolute best performance to you need to adjust the sprocket position relative to the camshaft by off-set dowels or by vernier sprockets like those in the photo, using the procedures described by Stresscrax in the earlier message above.

Image

If you were one sprocket tooth out on the timing chain on one of the wheels the two marks would be out of line by at least one tooth gap. The marks do move slightly when you adjust the tensioner from slack to the correct tension.

See:
engine-exhaust-cooling-f39/clay-test-checking-clearance-between-valves-pistons-t26441.html?hilit=clay%20test#p175126
for some more pictures
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PostPost by: billwill » Sun Apr 28, 2013 3:50 pm

rdssdi wrote:Sorry been a long day substitute "new" for "now". Sorry


You can re-edit your own posts you know. There is a button at to right of your posting. :)

I'd never get mine right without that facility. :?
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PostPost by: billwill » Sun Apr 28, 2013 4:07 pm

If you think about it deeply for a while, you will realise that, for any two marked sprocket wheels, the accuracy of the position of the marks pointing towards each other is actually set only by the pitch of the teeth and the length of each link on the chain and the current position of the main-engine-crank sprocket.

At top dead centre for piston 1, that establishes a fixed position of the sprocket wheels, then the fine tuning of the camshaft(s) is done by rotating the camshaft relative to its sprocket, not the other way around. (rotation done by offset dowel or vernier hub on the sprocket wheel).
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PostPost by: SJ Lambert » Mon Jan 26, 2015 11:38 am

image.jpg and


This pair of new sprockets are marked with one dot & one line each. I've offered a very old sprocket (part number 105E - 6256-3) up to them and it appears that the dots match to the old sprocket.
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