i motor cam timimg

[Knockenwelle]

So the motor's got about 280 miles on it now, and runs beautifully. I've been having fun with an unmuffled x-pipe, too... What a sound as it climbs onto the cam!

As for a pic:

[Devil Inc]

Any ideas on possibly marketing that bad boy?

I'd be interested.

[eugeman]

Cool pics on that site. I speak passable German--there's some good tech there, too. The cam gear is finished. Turned out really good--nice tight zero fits everywhere. Got the cam degreed last night, and I'm really glad I have an adjustable gear! Took about 7 crank degrees (3.5@cam) to get the timing right! Also didn't have enough V-P in straight-up setting, but I do now.

I ended up taking .007" off the block (yep, it was that far off!) and .020" off the head (.007" needed to clean as well!). No wonder people have head gasket issues with used motors...

Which m20 engine were you starting with before machining?

[Knockenwelle]

I dunno about selling these... It took me about 8 hours of work, and the multiple setups were a big PITA. Keeping everything dead-nuts accurate and concentric is critical, as you can imagine, which takes lots of patience. Also, I did this in a conventional shop-no CNC, all by hand. I made my part in SolidWorks, then created a dimensioned shop drawing. I also had to make two fixtures/jigs. For what I'd have to get for one of these, you'd probably not save any coin over VAC's. Plus, to be quite honest, I don't want to be blamed for trashing someone else's motor if something ever went wrong, or cam timing was set incorrectly. Also, I really just don't have the time right now between school and work and playing with my new track toy to make these. Thanks for the interest, though.

The M20 I built was the stock short-block (numbers matching) from my car (1991 325i, M20B25, USA spec), and a used core head (though aparently untouched) from a parts car, cause some idiot PO ruined my original one with head bolt girdles--smashed the rocker shaft bosses to pieces (literally!)

[Dyno4mance]

Cool pics on that site. I speak passable German--there's some good tech there, too. The cam gear is finished. Turned out really good--nice tight zero fits everywhere. Got the cam degreed last night, and I'm really glad I have an adjustable gear! Took about 7 crank degrees (3.5@cam) to get the timing right! Also didn't have enough V-P in straight-up setting, but I do now.

I ended up taking .007" off the block (yep, it was that far off!) and .020" off the head (.007" needed to clean as well!). No wonder people have head gasket issues with used motors...

Sorry to bring this up from the dead....but could you quickly do a "how to" on degreeing in the cam....I am having a hard time doing mine...Thanks

[Mike]

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[Knockenwelle]

Since the head is aluminum, you have to bolt on a piece of steel somewhere convenient for the indicator base. But that's getting ahead... You should already have the degree wheel bolted securely to the crank, and have found exact TDC before the head goes on. It's no fun trying to get a read on the M20 valvetrain with beehive springs; I used a small but powerful magnet stuck to a retainer to provide a stable read point for the indicator. Due to the design of the cam and follower interface on the M20, the rocker ratio changes quite a bit through the cam event, which makes finding a lobe centerline (as supplied by Schrick)--NOT the same as max lift angle, in this case--quite tough to find. I used opening and closing events, and also ended up plotting an Excel chart of valve lift to cam degrees for the purpose of clarifying lobe centerline, and future reference about the lobe profile. Have fun!

Oh, and there's no need to torque the head on for all this; just snug a couple bolts so you can pull it off and use some clay to check V-P clearance as you adjust the cam. Degreeing mine made the difference between certain impact and OK.

[guibo09]

if one planes the head and block only for straightness, puts in hi comp pistons and say a 288 cam, will one need to degree the cam also? or is this only for decked heads like yours?

[Knockenwelle]

I've never built a race motor without degreeing the cam. It's like getting married without sampling the goods...

You can always risk V-P contact or untapped horsepower, but should you? That's your call. If you're building engines, it's a skill you'll want to learn eventually.

[guibo09]

I've never built a race motor without degreeing the cam. It's like getting married without sampling the goods...

You can always risk V-P contact or untapped horsepower, but should you? That's your call. If you're building engines, it's a skill you'll want to learn eventually.

alright. but what is the goal with degreeing a cam? is it simply lining up the center of the cam lobe with TDC of the piston? or is there more to it (ie adding timing does X, retarding it does Y)

[Dyno4mance]

I have the same cam as you and also the same springs.....
What data did you use with the schrick cam?
I have a sheet but I am not sure what the values mean...
For example
Cam Lift (Valve lift) I/E (mm) =7,3 (11,4)
Duration degree CRA Intake/Exhaust peak timing= 288 288/ 110
Valve timing degree CRA IO-IC-EO-EC =34 74 74 34
Valve lift @ TDC I/E (mm) = 2,8
Valve Clearance I/E (mm) =0,25/0,25

Give me some pointers as to how you found the lobe centerline...I did this on a SOHC engine 20 years ago and I have forgotten the formula..
If tou measure the lift of the intake cam with the dial indicator what do you measure then with the exhaust valve ?
Thanks for all the help so far

[Knockenwelle]

Yep, those are the same Schrick numbers I had to work with. Pretty lacking for such a high-dollar camshaft, but whatever. I used the opening and closing numbers, and just compared them to the angles I got off the degree wheel at a given valve lift. I don't know what their valve lift spec, or lash spec for checking is, so I equalized the difference between specified and observed opening and closing points to get started. Remember LSA is the only number given in cam degrees; double it for crank degrees. As for formulae:
Duration=(I/E)O+(I/E)C+180 (34+74+180=288)
Int centerline, assuming symmetric valve lift profile (probably NOT for Schrick)=288/2-IO (110)
Exh centerline=288/2-EC (110)

The lobe centerlines work out mathematically, as they should. The numbers also indicate that the cam has zero advance ground into it. For more math, check out Comp Cams website for technical help. They have some very good articles on degreeing cams. I ended up spending more than half a day making sure my numbers were right and playing with the timing.

[Knockenwelle]

Guibo, as for the point of degreeing the cam, your goal is to align the valve timing events with specified crank position. This number is determined by the cam grinder. You can adjust cam timing ON A DYNO to see if small changes result in better torque. This depends primarily on how the cam works with the head(s). M20s are different beasts, but GENERALLY for moderate builds, advancing the cam moves the torque peak lower (RPM) and a tiny bit higher(#). Retarding the cam from zero results in moving the torque peak to higher RPM, sometimes resulting in more horsepower. Retarding the cam too far will lose much more power than over-advancing, due to the huge influence the IC point has on cylinder pressure.

So other than FINE tuning on a dyno, the point of degreeing the cam is to ensure it is synched with the crank exactly where it should be for performance and clearance optimization. In the case of my Schrick, I installed it "straight up", right on spec with advertised values.

[guibo09]

Guibo, as for the point of degreeing the cam, your goal is to align the valve timing events with specified crank position. This number is determined by the cam grinder. You can adjust cam timing ON A DYNO to see if small changes result in better torque. This depends primarily on how the cam works with the head(s). M20s are different beasts, but GENERALLY for moderate builds, advancing the cam moves the torque peak lower (RPM) and a tiny bit higher(#). Retarding the cam from zero results in moving the torque peak to higher RPM, sometimes resulting in more horsepower. Retarding the cam too far will lose much more power than over-advancing, due to the huge influence the IC point has on cylinder pressure.

So other than FINE tuning on a dyno, the point of degreeing the cam is to ensure it is synched with the crank exactly where it should be for performance and clearance optimization. In the case of my Schrick, I installed it "straight up", right on spec with advertised values.

very interesting. thanks for the great and relevent insight.

when i build my stroker, i will start off by checking the degree of the cam and from there decide if i need to buy an adjustable cam gear. im ok with leaving the couple of % in power on the table from not fine tuning on a dyno.

[Knockenwelle]

You're on the right track: it's always a good idea to check. There are potential errors resulting from cam-to-crank centerline measurement (decking), cam gear defects (not likely on an M20), timing belt tension or teeth, cam dowel position (this is a big one, and fairly common, especially with cheaper cams), etc... Forgoing dyno time, just stick with the cam manufacturer's specs and shoot for those numbers.