Indexing adjustable cam gear

[Mikesmalaga72]

Anyone here have insights how to properly set up an adjustable cam gear? Ireland eng instructions wont download or send copy if you have them. Thanks!

Edited March 31, 2023 by Mikesmalaga72
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[Schnellvintage]

This was copied from their (IE) technical articles, "M10 Rebuild Cylinder Head Introduction."

 

M10 Cylinder Head Resurfacing and Its Effect on Cam Timing The published standard head thickness is 5.075”. For every .035” removed from the standard head thickness the cam timing is retarded by 1°.

 

fwiw,

Matt

 

 

[kbmb02]

4 hours ago, Mikesmalaga72 said:

Anyone here have insights how to properly set up an adjustable cam gear? Ireland eng instructions wont download or send copy if you have them. Thanks!

 

I think you’re asking about cam timing … requires data (accurate camshaft card), tools, measuring. -KB

[TobyB]

Yuppers-

 

ideally, degree the cam, tdc the crank, assemble the valvegear, align the two, snug the bolts.

Degreeing the cam is not hard, but requires some precision and persistence.

 

t

 

[Schnellvintage]

Thanks Ken for the pic.  That is the absolute correct way to degree a cam on these engines.  

[Mikesmalaga72]

Thanks for the valuable info guys...

So is it also true the purpose of an adjustable cam gear is to determine when and where to place a desired power band of a camshaft should take place, or sole purpose is only for correcting of head milling dimensions or both? Thanks!

[Tommy]

It's kinda both. First get it right and then if you really know what you're doing you can tune it slightly to the direction you want.

[Tommy]

But most of the choice is done when you've selected the cam.

[John76]

13 hours ago, kbmb02 said:

requires data (accurate camshaft card), tools, measuring.

Great picture Ken!

What does the rest of the degree wheel look like?

How do you know when the cam is exactly in the right spot (0 degrees on degree wheel)?

This is when both intake and exhaust valves are closed, but it looks like there can be quite a bit of adjustment.

[TobyB]

Yeah, that's the rest of the story:  to degree a cam, the usual procedure is to roll it through 360

while graphing the lift on the intake and exhaust.  A cam degree wheel helps, here.

Then, the starting point is usually whatever the grinder says for valve openings and closings*

and you do an initial timing alignment between crank and cam.  

THEN roll it through 720 crank degrees to see if all 4 events happen in time^

and adjust the cam as applicable.

 

THEN decide if you want to favor torque or top end, and cheat it one way or the other.

With a SOHC, there are always pretty painful trade- offs, so very seldom do you find lots

of free go by moving it more than a cam degree or 3.

Then take it to the dyno and see what you bought, and if you can find that little

bit of extra free go that HAS to be in there somewhere.

With DOHC, individual cam timing (and grinding) can make a big difference-

BMW's dual vanos gives them a LOT (30ish crank degrees?) of adjustment.

 

t

* the open time is usually specified at 0.050" or 1mm, as the 'take up ramp'

often goes on for more than 45 cam degrees.

 

^it's very common to have a cam that doesn't exactly agree with what the cam card says-

then you get to make phone calls, adjust your setup, and see if you can decipher what the

person who originally designed the cam had in mind.  And then take your best stab at it.

[Cabbage Fumes]

Toby gives a good description of the process. To answer the "why", it's to set the cam to where the cam card says things should be happening. A pre-designated degree'd gear like the one IE sells is basically useless. You need a slotted gear so you can put it where it needs to be. Also, you can't tune with a non-slotted gear with any real success.

Depending on who ground the cam, you may need to twist that thing a lot more than +/- 2º to find nirvana, which is pretty often the case, especially with a thin head.

[Markster]

Hi - this is a great bunch of info!  I am wondering what are the symptoms of an engine that has the shaved head and timing has not been “corrected”? 
 

i basically eyeballed the tdc - not knowing all of this.  
 

rough idle? Blow by? Valve’s opening too soon or too late? What symptoms then? 
 

 

[John76]

17 hours ago, Markster said:

I am wondering what are the symptoms of an engine that has the shaved head and timing has not been “corrected”? 

I'm wondering the same! 

 

25 years ago, I had my (BMW) head rebuilt (guides, seals, valves, rocker arms, rocker shafts) but never thought to ask if the machinist shaved the head. The block has never been out of my car and the deck is clean and straight. Original cam chain (looks new) and sprocket lined up per the service manual during assembly.

After reading through this post, I'm hoping I didn't leave some "horses" on the workbench or "psi" out of the combustion chambers.  I've only driven 5k miles... and car runs great. Could it be better with a cam tweak???

Thanks,

John

 

[Son of Marty]

John, did you pull the head due to a blown headgasket? If not I would assume a light skim to true everything and if thats the case your timing should be fine. Changing cam timing on our sohc engines your going to move the power up or down  but by shifting to gain top end will weaken the bottom end and visa versa.

[John76]

3 hours ago, Son of Marty said:

John, did you pull the head due to a blown headgasket?

No... I pulled the head for a valve job at 137k miles. It was burning oil and the valve stem seals were leaky.

This was done in 1998 ... and the head sat under my workbench (lubed and covered) on a wood stand.

This started my "project creep" which resulted in my car sitting on jackstands in the garage for 19 years!

Retirement gave me the time to put everything back together and I've been driving, enjoying, and "tinkering" since 2017.

I was intrigued by the "one cam tooth adjustment" that dramatically improved the compression test numbers.

 

John