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Cam/Vernier Gear/Shims? 

 

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 Post subject: Cam/Vernier Gear/Shims?
Posted: Mon Aug 29, 2005 9:37 pm 
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Aaaah - Can't for the life of me figure this out.
I'm looking at whacking a cam in the motor (EL/I6)
Can you guys help me out with some answers? I'm confused as hell :oops:

What the hell is a Vernier Gear? Is it essential? Does it allow the cam to run better or be more easily adjustable?

What is involved in 'dialing in' a cam? Is it do-able by the average mechanic? Do I need a dyno to do it properly?

I understand the concept of and the difference between Billet and Re-ground cams, and the need for shims.

Do the valve stems/seats/springs/whatever need to be changed? (Its only a fairmont taxi motor, not a ghia or an XR) If so, again, is it do-able in a reasonable workshop?

I think thats it for now! Cheers :D

 

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Posted: Mon Aug 29, 2005 9:44 pm 
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Image

that is a vernier gear. Lets you set the cam timing right (loosen with allen key and move the sproket without moving the cam). Not needed unless the cam isnt ground accurately (it happens). Ive had this in my car since I recon'ed the engine and it has always been set = stock.

You can dial in a cam youself if you have a dial indicator. Its not hard.

Billet cam is ground from a blank and is the perfect size for engine but is more expensive. Regrinds are ground from a stock cam and have smaller lobes so require shims.

Should change springs if you pick a cam with >480 thou lift.

 

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Posted: Wed Aug 31, 2005 5:22 pm 
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Yep - that pic is the "SLOT" ADJUSTABLE cam gear for these motors.

It is not a "Vernier" adjustable gear BTW - a vernier involves meshing of two sets of differently piched teeth which enables very fine adjustments in between the positions possible by moving either individual teeth set by one graduation.

 

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Posted: Wed Aug 31, 2005 11:14 pm 
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Aha. Taa guys.

Obviously a billet cam would be easier to install... why do most people go for re-ground cams?

Why do the larger lift cams require firmer valve springs? Why does everyone change the valve seals or stem seals or whatever?

 

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Posted: Wed Aug 31, 2005 11:25 pm 
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re grounds are much cheaper, BTW if a cam gear is only needed is the cam isnt ground accurately then why do JMM use them with their cams?
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Posted: Thu Sep 01, 2005 10:39 am 
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Adjustable cam gear is always a better idea than non adjustable as it allows the correct timing to be precisely set. Even in the case of a std cam where all things being equal the timing will be "near enough" just with a non adjustable gear, an adjustable one will enable that timing to be set absolutely spot on - but the performance benefit will not be as great as with a "performance" cam so it's not really worth bothering.

When you go to a modified cam then being able to adjust it precisely becomes pretty much essential - it's a big ask I think for modified cams to be ground in such a way that they end up spot on when bolted up with a non adjustable gear - especially regrinds (billets I suspect give more "room" for the grinder to position the lobes so that the timing is correct in the nominal std gear position). and in the case of performance cams you can also adjust the power up or down the rev range to some degree.

Firmer valve springs are required because with a higher lift cam there's more travel happening between the closed position (cam base circle) and the open position (cam lobe tip) of the valves - all of this travel of the valves still needs to happen in the same time period tho (just over longer distance) - so if the valve springs aren't hard enough the cam can "outrun" the valve's ability to stay with it (strictly speaking we're talking about the cam followers staying in contact with the lobes) and you get a situation where at best the valves are not operating according to the true shape of the cam (the valves are running "late") and at worst you'll have mechanical issues such as excessive lash and/or the lobes smacking into the followers while they're still travelling in the opposite direction etc. (ie. flutter and bounce). All this is more noticeable at higher revs.

People generally replace the stem seals simply because it's a good opportunitly to do it - ie/ while the springs are being changed over the seals are handily accessible. It's more of a preventive maintenance thing than a necessity.

Replacing the springs is not a difficult job - for example, I recently had my stem seals replaced because I had at least one that was leaking. I dropped the car off at 7.30 am and it was ready for pickup just after lunch - the work they did was essentially exactly the same as would be required to replace the valve springs (ie. they had to take the rocker assembly off and remove the springs to get to the seals) - and in fact without messing with the stem seals, just replacing the springs would be a bit shorter job. And replacing the cam would only be a few minutes work with the engine at that state of disassembly too as all they'd need to do is remove the cam gear bolt, lift out the old cam, lay in the new cam and reattach the cam gear (and swapping out the gear itself would only be a couple minutes extra too).

 

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Posted: Thu Sep 01, 2005 1:50 pm 
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Blu Falc wrote:
BTW if a cam gear is only needed is the cam isnt ground accurately then why do JMM use them with their cams?


ummm - probably because they cannot guarentee the cams are ground spot on. JMM do not grind there own cams, that work is outsourced to anouther popular cam company. Oh, and have you seen the price they charge for the gear compared to everyone else? If I was charging that price I would tell everyone they needed one as well.

 

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Posted: Wed Sep 14, 2005 12:15 am 
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Where else can you get the gear from and how much cheaper is it than jmm

 

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Posted: Wed Sep 14, 2005 1:55 am 
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If you get a stange 2 wade you shouldn't need the Vernier Gear or to bother with dialing in.
Shims are a peice of piss to do for regrind cams - just remember to get new hydrolic lash adjuster retainer clips, dirt cheap at your local auto store but they'll usually have to order them in...
it is very confusing for the novice, i had to ask heaps of questions on here when i was doing mine. well worth it in the end though.

get a mate round and a couple of beers and it actually becomes quite a fun arvo to change it. we snaped a socket on mine, and had to wheel the motor bike through the house and down stairs so we could go get a new one and had al sorts of funny little stuff go wrong.

 

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Posted: Wed Sep 14, 2005 2:02 am 
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regarding what can you should buy, its much of a muchness as everyone has their own opinion and experiences.

most people you will find have a wade and have a very good result and are happy with what they paid and what they got (bang for your buck)

Joe from crescent motors in sydney also does cams now and recently got 148rwkw from his stage2 in yobbofords wagon from a 110/115 previously stock it was (5spd too).

Crow cams are good, dynotec, list goes on and on, it depends what you really want but you will find most people havent had problems with reground cams.

I suggest yo ucall wade or joe @ crescent as they both do packages (joe does venier and cam kit) and wade i think can also do it too for you...
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Posted: Wed Sep 14, 2005 2:09 am 
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get a vernier gear.. chuck it in at the same time as the cam.
for the $100 it costs, its worth doing at the same time.
better to have the cam dialed in 100% and get EXACTLY what u paid for then to just hope for the best.

 

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Posted: Thu Sep 15, 2005 1:48 pm 
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ive got an adjustable cam gear and its not hard to adjust the timing... just some spare time needed to pull the rocker cover off..

 

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