Cam timing with DC20's

[quint22cp]

In Wayne's book there are two methods for setting the cam timing.

I have DC20 grinds from Cam Grinder, has anyone timed these and which method did you use ?

[304065]

A DC20 has .475" intake valve lift according to John's website.

By comparison, a "high-lift" cam like the "S" cam Wayne uses as an example in his book has only .455" intake lift.

So what you've got in the DC20 cam is "a very high-lift cam indeed" which calls for the procedure for high-lift cams in Wayne's book.

Good luck!

[alphie]

Yes, I installed the DC20 cams last year and you need to follow the High-Lift cam procedure - sort of.

Wayne's procedure makes more sense if the cams have the big nut end. That allows you to move sprocket while holding the cam steady. You can't do that if you have the bolt-style cams. In that case you turn the cams to the correct dial indicator setting, then remove the locking pin, then turn the cams 720 to TDC. Insert locking pin and retest.

This is off the top of my head for the bolt-style procedure - you should probably do a search for that method, but I do remember wayne's method didn't work as you can't hold the cam steady and turn the sprocket at the same time.

[KTL]

I agree with Alphie. The Wayne Dempsey high lift cam timing method doesn't work with the bolt-end cams. You can't counterhold the crank and move the cam because there's nothing you can use to turn the cam!

Here's how I did it:

1. You can use the bolt that secures the sprocket to the cam IF you must turn the cam in the clockwise direction to achieve the desired lift measurement. If you must turn the cam in the counter clockwise direction, this obviously does not work because the bolt will loosen. The key here is to start out your timing process such that when you get to TDC overlap, you find that you are deficient in lift (dial indicator reads less than desired) and you must turn the cam clockwise to gain lift. So instead of setting the cams with the 930's up to start, maybe turn them a wee wee wee bit counterclockwise.

2. Disobey Wayne's method of holding the crank and turn the crank the direction needed to get nearer your lift measurement. I believe Wayne's recommendation to hold the crank and move the cam is due to the possibility of the cam moving on account of the force of the rocker arm acting on it. With the DC 20 cam profile, I did not find that the cam wanted to move when setting the timing. I'm a complete weirdo and have to do things way too many times before being satisfied with my results. Point being, I set and reset and re-reset the timing many times and not once did the cam move on its own under spring pressure.

I had hoped to devise a tool to allow us to rotate the cam in either direction when setting the timing. First I simply tried using a M12x1.5 nut to use as a jam nut with the cam bolt. Turns out the cam bolt is a bit too short and I couldn't get enough thread engagement inside the cam with the jam nut on the bolt to feel comfortable tightening the jam nut. The next step would be to get a longer M12x1.5 bolt to gain more thread engagement. Well I was running of time and did not have the opportunity to get another bolt and see if this would work. Maybe next time.......

Another thing to note on the DC 20 cams. I had a problem setting my cams to the desired 2.2-2.4mm lift at TDC overlap. I could not get adequate piston-to-valve (P-V) with it set at 2.3mm. I only had about 1mm, minimum is said to be 1.5mm. So I ended up backing off the lift to 1.85mm to get good clearance. Hopefully my case was a rarity and others do not have this problem. Point being, BE SURE TO CHECK YOUR P-V CLEARANCE WITH THESE CAMS, ESPECIALLY WITH STOCK MOTRONIC OR CIS PISTONS. I think pistons with the valve reliefs are a wise idea, especially if you're building a bigger displacement engine like a 3.4 or 3.2 short stroke.

And you must check the P-V elsewhere besides TDC overlap. My closest clearance location was at a crank angle maybe 10 degrees past TDC

[alphie]

Excellent post KTL!

I experienced the same thing. When I did my P-V clearance check I found I had .25mm clearance!!!

I took this to be the fault of the higher compression max moritz CIS pistons. I ended up machining the valve pockets 1mm on the intake side. That got my clearance to just above 1mm. In hindsight I wouldn't have gone with this combination, I have since acquired the mahle sport pistons and DC40 cams.

-Rob

[KTL]

Thanks Rob. I'd like to add one more thing. My P-V clearance deficiency was on the intake valves, due to the "ripple" in the stock Motronic piston shape. I had no problems with P-V clearance on the exhaust side.

[alphie]

same here, no probs on the exhaust side.

[Nux]

Originally Posted by KTL

I agree with Alphie. The Wayne Dempsey high lift cam timing method doesn't work with the bolt-end cams. You can't counterhold the crank and move the cam because there's nothing you can use to turn the cam!

Here's how I did it:

1. You can use the bolt that secures the sprocket to the cam IF you must turn the cam in the clockwise direction to achieve the desired lift measurement. If you must turn the cam in the counter clockwise direction, this obviously does not work because the bolt will loosen. The key here is to start out your timing process such that when you get to TDC overlap, you find that you are deficient in lift (dial indicator reads less than desired) and you must turn the cam clockwise to gain lift. So instead of setting the cams with the 930's up to start, maybe turn them a wee wee wee bit counterclockwise.

2. Disobey Wayne's method of holding the crank and turn the crank the direction needed to get nearer your lift measurement. I believe Wayne's recommendation to hold the crank and move the cam is due to the possibility of the cam moving on account of the force of the rocker arm acting on it. With the DC 20 cam profile, I did not find that the cam wanted to move when setting the timing. I'm a complete weirdo and have to do things way too many times before being satisfied with my results. Point being, I set and reset and re-reset the timing many times and not once did the cam move on its own under spring pressure.

I had hoped to devise a tool to allow us to rotate the cam in either direction when setting the timing. First I simply tried using a M12x1.5 nut to use as a jam nut with the cam bolt. Turns out the cam bolt is a bit too short and I couldn't get enough thread engagement inside the cam with the jam nut on the bolt to feel comfortable tightening the jam nut. The next step would be to get a longer M12x1.5 bolt to gain more thread engagement. Well I was running of time and did not have the opportunity to get another bolt and see if this would work. Maybe next time.......

Another thing to note on the DC 20 cams. I had a problem setting my cams to the desired 2.2-2.4mm lift at TDC overlap. I could not get adequate piston-to-valve (P-V) with it set at 2.3mm. I only had about 1mm, minimum is said to be 1.5mm. So I ended up backing off the lift to 1.85mm to get good clearance. Hopefully my case was a rarity and others do not have this problem. Point being, BE SURE TO CHECK YOUR P-V CLEARANCE WITH THESE CAMS, ESPECIALLY WITH STOCK MOTRONIC OR CIS PISTONS. I think pistons with the valve reliefs are a wise idea, especially if you're building a bigger displacement engine like a 3.4 or 3.2 short stroke.

And you must check the P-V elsewhere besides TDC overlap. My closest clearance location was at a crank angle maybe 10 degrees past TDC

Just a big thank you to All you guys in the forum. Found this 10 year old thread before timing the DC20 cams in my 3.2SS (Mahle 9.3 cr). You guys are spot on: had way too little clearance with 2.2mm, so ended up timing them at 1.8 and got it right.

Cheers!

[Neil Harvey]

I started replying on this forum after we got involved in Jeff’s project. Reading some of the many posts asking “how to” I found a lot of misinformed and in my opinion wrong information being told.

A lot is old historic info and many of the assembly methods are “ball park” at best. I think if more was told “why”, and be “careful because”, many here would have a better understanding.

Cam timing seems to be one of the areas that instills fear into many. It doesn’t need to be as its easy, if you understand exactly what you are doing. But there are some short cuts and basic inspections that should be done prior.

I read here, where cams were timed based upon the clearance between the Valve and the Piston. This is wrong in all aspects. Sure, you don’t want the valves to crash, but why the compromise. In most engines, small changes in cam position makes a big difference in performance. What is wrong? The piston or the cam?

If you are rebuilding your engine, why have you not set a performance goal ahead of time? Were the Pistons and the CR chosen and the cam spec all configured together? If you are using existing Pistons, why was that cam chosen? Was the cam timing known at the time? All these parameters need to be decided upon before you buy anything.

Cam profiles and positions should be changed based upon the performance required. More response at the lower engines speeds, advanced more and retarded if more upper end performance required. In these 2V engines with a single cam, the LSA controls the exhaust valve timing if the base setting is done with the Intake Valve.

I would like to suggest some checks to be done before you buy a camshaft. This requires a degree wheel to be used. The way it is done by lift at TDC is ball park and close. There are too many possibilities for error and differences from one side of the engine to the other. The correct way should be to use a degree wheel and time the cams at full lift.

If you have a degree wheel fitted, you can find true TDC by splitting the piston dwell at TDC. You may be surprised just how many crankshaft degrees the crank turns as the piston goes over TDC. You do this before fitting any of the Cylinder heads. Use the same dial indicator “you used to use” when timing the cams.

After you have true TDC, fit one head with the valves only. You could use some soft helper springs. Hold the Exhaust valve up so it doesn’t interfere with the Intake Valve. A simple rubber band wrapped around the valves and a stud works great. Now rotate the engine 1 turn clockwise, (always turn the engine in its proper rotation) and stop at 20° BTDC. Measure each valve drop, from the valve seat to the Piston making sure the valve head goes into any pockets without side interferences. Repeat this every 5° until you have gone to 20° ATDC. Now you have a maximum lift number each valve can move off its seat until it touches the piston. Subtract any clearances you want, and this will be the maximum lift the cam you chose will need to have, at whatever position you decide upon. This may save timing the cams twice.

A good camshaft supplier will be able to suggest the crank position to start off with and the actual valve lifts from 20° BTDC to 20° ATDC at that crankshaft position. If the valve lifts are greater than the drop measured, you have interference.

This way, before you buy any Camshaft, or do any cam timing you will know your limits and be able to choose the cam that will give you maximum performance without having to compromise on its settings.

Timing the cams with a degree wheel is not at all difficult and with the cams at full lift, you do not have issues with the cam wanting to roll back. You only need to time the camshafts with 1 intake Rocker arm fitted each side. If the cams are well made, knowing the maximum lifts allowable, the LSA you are using, the timing will be a lot more accurate. Always fit a Rocker arm to the exhaust side and double check your clearances. Make sure you set the valve lash before performing any timing on either valve. The camshaft provider should give you a hot lash number the camshaft was design to have. Experience will tell what the cold lash number is, typically somewhere between 0.004” – 0.008”. These should always be checked hot, after the first run in period as they do change.

I think I have something on our web site on how to time the cams using a degree wheel and those that need further help, can contact me through our web site.

[Nux]

Thank you for a thorough reply.

I did in fact consult John Dougherty before I purchased these cams. He said these would work with my current setup. He also advised me to time them at 1.8-2.0.

I've since read many times on this forum how people time them at 2.2-2.4. Accordingly, I consulted JD once more and he informed me that I could advance the cams if I had CR of 9.3 or more.

So since I had measured my static CR to 9.3, I tried the advanced setting first. It did not provide enough clearance however. I then timed them at 1.8. Just did a seach, and found others with same engine spec had the exact same experience.

The experience and knowledge of the people in this forum is one of the main reasons that I use it. I also used your info on my engine build and choice of piston rings - so thank you again.