i motor cam timimg

[Knockenwelle]

So I'm putting the final touches on my warmed-over M20 buildup. The head's been cleaned up (ports, chambers, pockets, trick valve job, port-matched intake), and the compression is now 9.6:1 with stock pistons, thanks to some decking. I have a Schrick 288 cam in the mail. I know I'm going to need to correct cam timing, so I'm putting together a list of options. I can:

Use an adjustable cam gear from Cosmo or VAC. These are the only two I found, but please tell me if you know of others. Downside: cost money.

Make my cam gear adjustable. I am a competent machinist, and have already worked this out. Bonus: FREE! Downside: PITA machining.

Use a cam gear off an Eta? I've seen some threads here that suggest I may be able to do some mix+match until I get it right.

Use an offset dowel pin. Anyone know where to get one? Diameter is 8mm.

And for the record, the cam gear has 48 teeth. Setting the cam timing off a tooth results in a 7.5 cam degree/15 crank degree change, which is WAY too much for anything.

[Dyno4mance]

Unfortunately because you have skimmed the head you will need to degree the cam to find the lobe centerline...this involves using the info from the cam card, an adjustable cam gear (probably cosmo they look like they would not have issues) a dial indicator and stand ( not a big deal if you are a machinist), and a crank protractor (you can print one off the internet)....if you do not do this you will almost certainly leave a lot of the power available with a cam upgrade back in the box....

[SpecM]

sounds like you've got some fun ahead of you

[Knockenwelle]

Thanks for the replies. Yes, I plan on degreeing the cam; something I'm familiar with and have the tools and knowledge to do correctly. Hence the need for an adjustable gear. So Dyno, you like the Cosmo version? Anyone else have experience with either/others?

[digger]

NUKE make a top quality unit, it is available from PPF.......as always with quality parts they aren't cheap but atleast you'll only have to worry about setting it correctly which is not as important as many will lead you to believe as long as its within about +/-4 degrees its fine

[Dyno4mance]

Thanks for the replies. Yes, I plan on degreeing the cam; something I'm familiar with and have the tools and knowledge to do correctly. Hence the need for an adjustable gear. So Dyno, you like the Cosmo version? Anyone else have experience with either/others?

To be quite honest I am in the same boat as you...Not wanting to spend a great deal on an adjustable cam gear but realizing it would be foolish to slap an expensive cam like the schrick in the head without degreeing it...
I have not seen a Cosmo gear in person but an adjustable gear is not extreme engineering assuming the pitch of the teeth is correct the only other thing to consider is if the thing clamps down and stays in the position it is put in and the allen bolts do not back out....
Unless I read anything to the contrary in the next 2 weeks I will probably purchase a Cosmo one myself as others I have seen are double the price...but I will look at material and design fairly closely before I close this chapter in my engine build.
Keep me posted with what you choose...

[Knockenwelle]

I have decided that in my broke-ass college student budget, there is no room to purchase such frivolities as made-to-order adjustable cam gears, despite their overwhelming importance as part of a proper cam install. So I'm going to make one. I'm using my stock cam gear, and basically duplicating the similar designs I've seen from a few different manufacturers, with a little extra ingenuity thrown in to insure all pieces are kept concentric. This involves a rotary mill table, two custom fixtures/jigs, and a piece of 6061 about 4.3" dia. That's all I'm gonna say, but stay tuned as I will be posting the results of degreeing the Schrick 288 on a .027" total deck reduction with a stock gear... I hope +-10 crank degrees is enough adjustment.

[Dyno4mance]

I have decided that in my broke-ass college student budget, there is no room to purchase such frivolities as made-to-order adjustable cam gears, despite their overwhelming importance as part of a proper cam install. So I'm going to make one. I'm using my stock cam gear, and basically duplicating the similar designs I've seen from a few different manufacturers, with a little extra ingenuity thrown in to insure all pieces are kept concentric. This involves a rotary mill table, two custom fixtures/jigs, and a piece of 6061 about 4.3" dia. That's all I'm gonna say, but stay tuned as I will be posting the results of degreeing the Schrick 288 on a .027" total deck reduction with a stock gear... I hope +-10 crank degrees is enough adjustment.

Thats only 2.5 either way on the cam...why so limited movement if you are going to all the trouble of machining your own?

[Knockenwelle]

Nah, it's +-5 degrees at the cam. The total arc in the adjustment slot is 10 degrees long. crank degrees=twice cam degrees. Besides, with that much adjustment, I also have the option of advancing teeth and retarding gear, or vice-versa since there's overlap in the adjustment.

[Dyno4mance]

I hope +-10 crank degrees is enough adjustment.

to clarify you said that you had +/- 10 crank degrees which is equal to +/- 5 degrees on the cam...which is 2.5 degrees advanced or 2.5 degrees retarded which is what I said "2.5 either way"

[Knockenwelle]

Ah, I see the mix-up. I designed the cam gear with 5 degrees in both advance and retard directions (from zero), for a total adjustment range of 10deg at the cam

[digger]

+/- 5 degrees on the cam...which is 2.5 degrees advanced or 2.5 degrees retarded which is what I said "2.5 either way"

+/- 5 degrees on the cam...would imply 5 degrees cam advance up to 5 degrees cam retard IMO.

[eugeman]

Try this link although it is in German, it translate enough for one to understand. It is from the e30.de website under the M20 section. It shows a couple of pictures on how one modified a stock cam gear to make it adjustable. While you are at it, go forwards and backwards on the pages as it has some other good info and many links on a stroker build.

http://wp1016621.wp027.webpack.hoste...m20seite34.htm

Although they don't advertise it on their website, and are EXTREMELY hesitant about selling you their last couple of ones, MM has a couple offset cam dowel pins left at $15 a piece. Jim said that they are a nightmare to install and I believe that they change your cam timing by 2deg, but you'd have to call them to confirm.

How much did you shave off to get 9.6:1 compression with stock pistons?

[Knockenwelle]

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...

[AndrewBird]

Got any pictures of the cam gear? I'd be interested to see the machine work.