Cam timing????

[mk1matt]

My cosworth cams come with a couple of locators at the back which you put a bar across and this times the cams.
But then i hear about people tweaking the cam timing and am wondering whats what????
My question is do i just set the engine up with this bar and if i do will this make the piston valve clearance as close as it would ever get??? I think that makes sense.

This is my cam profiles. Mine are the bottom 2. The 718 and tha 719.
http://www.cosworthusa.com/store/pc/viewPrd.asp?idcategory=25&idproduct=62

[Dave]

Don't know how relavent it is, but an interesting read.
http://www.burtonpower.com/technical_1/camshaft_fitting_timing.aspx
Have you got verniers then?

[mk1matt]

Yeah i read that artical earlier dave :thumb: And to time the duratec standard is really easy. I just need to know what to time the cams to :dunno: And if i time them with the bar in place will that put the valves as close to the pistons as they will ever get :dunno: As for verniers, sort of. The cam sprokets are held to the cams with friction washers so they are infinatly variable :thumb:

[Dave]

Purely guessing, because I don't know about such things.
The link you put up gives a "Bar timing" figure, so I guess they are suggesting that is where you start from. :dunno:
Says they are for a 2.3 though, isn't yours a 2 litre? Or doesn't it make much difference in this case.

[mk1matt]

The cams are 250 on a 2.0 and 270 on a 2.3.
Yeah i reckon the bar timing is a good starting point but does that put the valve as close to the piston as it will ever get :confused: I would hate to set it all up and then find i couldnt get the best out of the cam timing because i didnt have clearance.

[graham bahr]

i cant comment on valve piston clearance, although i would of thought you had a decent amount with the cutouts in those pistons.

how i read the cosworth link is that they are telling you where the cams will be timed in if you use the bar to set them,

now as for whether that will give the best setting for maximum power is another thing, dave walker always retimes them by meassuring the amount of valve lift on tdc.

this figure will vary depending on engine type, but a typical fast road cam will have as little as 0.080" full race cams more like 0.200"

either way i doubt your go far wrong timing them up with the bar and leaving it at that as your not looking for every last scrap of power at 8,000 plus rpm

[mk1matt]

Now that sounds more promising :thumb:
So all i really need to know now is if timing with that bar will put the valve as close as it can go to the piston as although i might not be trying to squeeze every last bhp out of the engine i would hate to not have the option.

[graham bahr]

all i really need to know now is if timing with that bar will put the valve as close as it can go to the piston as

i doubt it, but the only way you are going to find out is to build the engine either as a dummy build with an old head gasket on and some plastoscene on top of the pistons,

or just build it and play with the timing and meassure how much further you can push the valve buckets down before the valve hit the pistons, if you can find a way to lever the cam buckets down,

does this engine has hydralic or solid lifters, if its hydralic your wasting your time with either of the above methods

[mk1matt]

Solid lifters :thumb: The cams are directly over the valves.
They have caps that go over the valves that are differant depths for adjustmant.

[dobuy]

Don't know about Cosworth Cams, but I would guess they make them so that the bar is accurate. So I am pretty sure you will not smack your pistons if you set it up on the bar. On my car that uses Raceline 280 degree cams, there is a couple of degrees difference between the bar setting and dialled-in properly. So I think it is well worth checking them properly, as it can make a significant difference in power output. Mate of mine has done dozens of Duratec cam installs for a well known UK manufacturer and he played around with the cam timing on his own car recently on the dyno, made a big difference especially in the torque output.

[dangerousdave]

Matt surely you can time it all up on tdc using the bar and then swing each cam by hand and count how many teeth from a known point it is until it hits the pistons?

I would say for sure that the valve isnt as close as it can be to the piston at tdc because of reliability issues should they be fitted to an engine with pistons that have less depth to the valve recesses :thumb: Cam timing is a fine art, as far as im aware you want the inlet valve to just be starting to open around or just after tdc otherwise the piston travelling back up will force the mixture back out of the inlet port. I think there is a dwell period though where you can start to open the inlet early where the piston isnt really moving enough to reject the incoming mixture :thumb:

[mk1matt]

Funny you should mention dwell :thinking:
I've been finding my true tdc by following the advise on the burton web site using a cam degree wheel and a depth guage thinghy. Now the burton site says you can have around 10 degrees dwell on an engine. Mine is lucky if its got 2 :dunno: Theres nothing i can do about it so i guess it doesnt matter :D