What to look out for when regrinding cams...

[jeffro ra28]

If you want my opinion id say 250 @.050" duration and .430" lift is about all you would want to gain from a stock unwelded cam. 5mm thick shims are very thick! I personally wouldnt be going much more then that. Besides, cams being any larger would love big revs, the valvetrain with big fat shims wouldnt love the revs . Only because it increases the chance of the shim popping out, and we dont want that to happen!

[oldcorollas]

as RAd mentioned to me, the 18RG is shim under... so any increase in shim thickness is just lifting the bucket out of it's bore... how much is too much?

well it happens plenty on pushrod cams like the k motors and 18R... where you just grind the cam for ~$90 then adjust the rocker arms to suit.

But I dont know if that is considered dodge?

when you increase lift, at least of a K motor, then you have think about 2 main things...
first is how much lower the lifter sits in the bore, especially if you have machined the walls thinner, cos having too much will start putting undue stress and friction every time ti lifts (cos too much is pokin ou the hole)
second, you realyl should machine down the rocker towers by the same amount as the increase in lift, otherwise you bugger up the wipe of the rocker on the valve, and get large wipe with large force = baaad. more wipe near lowest load is much better.
of course you can not do that, but then your rockers and valves wear out faster and they need to be adjustmed more often and they are noisier (as they try and grind themselves to death )

but that is not so relevant here

[jeffro ra28]

OC, compared to how much of the bucket already sticks out and how much was in the bore i figured that an extra 2-3mm wasnt enough to upset anything.

If it was a very slim profile lifter and bore then it may be an issue but in the 18rg's case it quite high and i dont think it will affect anything.

EDIT: Again, at high rpms side loading for lifter would be magnified and may make the valve train a bit unstabble. But with the suggested cam specs high rpms wouldnt be in the picture anyway.

[RAd28]

Jeffro - what do you consider "high rpm"? I regularly see 6k in mine, but rarely as high as 7k, over that it just seems to make bad noises... i'm not game to hang around there long enough to find out if anything will happen...

[jeffro ra28]

over 8500 rpm things start to happen buddy.
My old stock 2tg only just took 8500 rpm before valve float

If the bottom end wont handle more revs. Then there isnt really any need in going cams a great deal larger then whats in it.

[RAd28]

I'm not sure what the bottom end will handle to be honest... but as far as i know she's still pretty tired, so should be getting something done about that too... I'm sure it'd capable of more then 7k though...

[jeffro ra28]

Perhaps just aim for some mildish sorta cams then. You wont have to go to thick with shims then aswell.

[RAd28]

is it worth buying 2nd hand unknown spec cams? is there any way to 'read' a cam to find out it's approximate duration/lift?

[RAd28]

anyone to check out for cams? I've got Tighe, Waggot, clive and kelford... will do a ring around tomorrow...

Cheers


EDIT: how on earth do you measure clearances for shims that are 4-5mm?? is it a matter of measuring clearances before removing the cams and doing some number crunching? then hoping you've measured it accurately enough?

[jeffro ra28]

usually the roundness of the point of the lobe indicates duration. The rounder the tip of the lobe the larger the duration. Experienced people can make geustimates. But its extremely rough and hardly a way to tell. The only reall indication that can be made is "thats not stock" or "thats huge". Otherwise get it doctored.

You can use the old shims and do number crunching and use thick feelers gauges or you can have one thick shim made with a known thickness close to the overall thickness of the required shims and go from there. Will be easier measuring the clearance with said thick dummy shim then using all your old thin shims and using thick ass, or mulitple feelers gauges together.

[RAd28]

Cheers, that's about all i could think of too...

Found a set of 2nd hand cams, might check them out and take the stock ones, and a micrometer to compare...

[SuperDave]

SuperDave - I believe there's Kelford Kams (not Cams) on the gold coast somewhere... they're a spin off company from Kelford Cams i believe..

I'm not too sure if they are or aren't, as I know nothing about either of them really.

[RAd28]

Okay, did a ring around today,

Clive Cams - $390

Tighe Cams - $210 - Grind, $520 - Build & Grind, $950 - New

Couldn't find Kelford Kams, the number i have has been disconnected... anyone got recent contact details?

Cheers

[jeffro ra28]

try waggot. had some good experiences with them.

[w810sc]

EDIT: how on earth do you measure clearances for shims that are 4-5mm?? is it a matter of measuring clearances before removing the cams and doing some number crunching? then hoping you've measured it accurately enough?

Inlet = Thickness of used shim + (valve clearance measured - 0.011in [which is 0.29mm] )

Exhaust = Thickness of used shim + (valve clearance measured - 0.013in [which is 0.34mm] )

Just substitute the recommended clearance you need for the valve clearance gap, I have shown the standard gaps 0.011' for intake and 0.013 for exhaust.

As for measuring the 4-5mm gap, dial indicators, feeler gauges, spacers; anything goes.