skimmed heads vs. mechanical timing

[jimbob-mcgrew]

once a head is skimmed, the leading side of the cambelts going to be loosened right, either upping the chances for a belt slip, or knocking out the timing a touch.

is this what a vernier pulley is primarily use for ? ... to take up that slack ?

[Andy]

yeah it will do.On my grasser engine my old head head been skimmed 1.5mm and as such the belt in the right timing position was flopping about like a soft nob.
As I couldn't run a vernier pulley (as per class rules) Id have had to run it slightly retarded

[Andy]

I have a new head now lol

[mowgli]

andy, surely you could move the timing peg slightly......it would be impressive for a scrute to find that

[mowgli]

once a head is skimmed, the leading side of the cambelts going to be loosened right, either upping the chances for a belt slip, or knocking out the timing a touch.

is this what a vernier pulley is primarily use for ? ... to take up that slack ?

this is one of the reasons I am against skimming for the sake of it.

unless there is surface damage, then they simply don't need skimming for normal road use.

in something like andy's competition class, skimming is rife to attempt to get some extra compression & thus extra hp, but it then has its downsides, like the timing being out, then the dizzy timing will be out too & the engine will be a sod to get running bang on unless you start 3d mapping or similar

[Andy]

that's why I binned that head.
what dya mean regarding scrutineering?
vernier pulleys not allowed but I could run it timed how I please

[jimbob-mcgrew]

i think he means moving the peg behind the pulley to compensate. a custom fix, out of site

[jimbob-mcgrew]

pretty sly mo, :)

[mowgli]

it would be tricky to get the peg in the right place, but it would pay with power

[dgbnova#1]

A trick bit of machining could easily see this done only retarding a few mm

as for the head skimming in that case can you not run thicker or 2 gaskets not that it matters but just a question

not a fan of skimming I just ask for a pass to check it removing dirt basically

[Andy]

You probably could but it would defeat the object really.

[Andy]

There is also a minimum thickness rule.
Not sure what it is though

[mowgli]

iirc they have a rule to limit skimming, on both the head & the cam carrier.

skimming the carrier will not help one jot with cam lift, but might help keep the hydraulic lifters from pushing down. maybe upping the oil pressure would be better

limiting skimming on the head will stop extreme cr, but not if there isn't a rule about decking the block.

re the cam peg.. i'd imagine any decent precision engineer would be able to sort something out. if i ever manage to build the e18se, i'll be looking at it.

[jimbob-mcgrew]

if i ever manage to build the e18se, i'll be looking at it.

you got one mo ?

whats that from, mk.1 astra gte ?

[mowgli]

nope, the 18se was the astra one.

gm never did an e18se, but i want to have a play at making one.

there is a box with the innards from joff's wifes old x18xe1 in my shed... i have some new valves from a 20seh(they fit the nova head but are larger diameter) i also have some afm's/ecu's off carltons with jetronic efi.. they have much bigger flaps & higher fuelling... the plan is to hunt out a cheap 1600 bottom end, and play.... its lack of funds at the minute that are slowing it up

[jimbob-mcgrew]

sounds like alot of custom fiddling, but will hopefully be decent when finished. good luck :thumb:

[mowgli]

not much custom fiddling really... i'm fairly well acquainted with a jetronic setup these days... i just want the fun of making the engine, as i've only rebuilt stuff using standard components for far too long & i love all the measuring/maths, crossing fingers when it turns over etc....

[John]

you still have your nova then Mike?

[mowgli]

yes... sadly on a SORN at the moment... voluntary debt management is very expensive, and my wife's shopping habits were too........

[Stuart]

Just remove the peg and time it as you wish and then make sure the bolt is tight (the zetecs had non pinned cam drives)

[John]

yes... sadly on a SORN at the moment... voluntary debt management is very expensive, and my wife's shopping habits were too........

Bad times Mate, save it for those rainy days! lol

[mowgli]

i was hoping for snow tbh, its way more fun

[burgo]

You can buy offset dowels that adjust by single degree's upto 7 degrees either way

[jimbob-mcgrew]

didnt know that.
kinda like this :

http://ecx.images-amazon.com/images/I/41DpJuMu3RL.jpg

[Stuart]

or, do away with the pin completely and be sure the bolt is tight :)

[burgo]

Exactly like that. Suppose depends how far it needs to go

[mowgli]

or, do away with the pin completely and be sure the bolt is tight :)

a friend had to mend one of those 1.25 fiesta engines that had no pegs or keys on its camshafts, just tapers & Loctite.

the nova 8v setup would need a little peg because 2 flat faces won't be as strong as a taper