Setting 4k Cam

[mighty_4k]

Hey guys will be putting my 4k and my newly ground cam back together over the weekend hopefully. Could someone please tell me how to set up the cam properly? Appertaley your not ment to put them on the standard marks like you would normally would with a standard cam, thanks.

[kdog30]

yeh id be sure its done right when you do it otherwise you will be like mine and have to try tune it every day to et it to run right

[philbey]

Which marks are you talking about? Your cam should be ground correctly aligned to the dowel pin. The cam gear has a factory mark on it to align your cam sprocket to the crank sprocket.

 

If you assemble it using the factory method, you should be fine.

 

The only reason you would change the cam-crank sprocket timing is because the cam wasn't ground properly.

 

What I think you are talking about is your Ignition timing; yes you will need to change it from factory. Larger, lopey cams have difficulty idling. There are two options to get around this, either advance your ignition timing (ie setting the marks differnt), or set your idle higher.

 

Advancing the timing is easy enough but without regraphing your dizzy, you can't get too much advance.

 

Lighter flywheels will add to the problem even more. My 5K has a big cam but a stock flywheel, so I get away with about 10 degrees advance and about 1200-1400 rpm idle.

[mighty_4k]

Thanks Philby, someone told me that I would have to set the timing marks differently I just assumed he meant the cam-crank sprocket timing but what you said about the Ignition timing makes a lot more sense to me. On that note isn't that one of the things they would sort out on the dyno when I take it in to them? Otherwise what am I spending my hard earned cash on? Also on my cam sheet it says for best results time intake valve fully open 105° degrees ATDC. I have no idea what the hell that means lol.

[altezzaclub]

Also on my cam sheet it says for best results time intake valve fully open 105° degrees ATDC.

 

Forget it, you can only set to factory marks unless you change the way the sprocket mounts.

 

The Datsun 1600 had two holes in the sprocket, two marks on the sprocket, and a mark on the backing plate. You picked either hole to align the marks, and we used to drill a third hole on the sprocket so we had 5deg, 10deg and 15deg choices, and a chain tooth was 16deg I think. That gave us a range of cam timings at a low cost.

 

You could do the same if you were keen enough, but just setting it to stock will do unless you're going full-time track racing with it.

 

If you put a protractor on the crank you could measure when max intake valve opening is. It should be close to that.

[philbey]

Timing will be straightforward, your dyno tuner will spend most of his time tuning your carbs to suit.

[mighty_4k]

Thanks guys set my timing chain up today on the standard marks. To save myself from starting a new thread how long would I have to run my engine in for before its safe for the dyno? I got my cam ground, headwork done, sidedraft carbs and a new clutch which has been used on a different k-series before but only for 1000kms. Haven't touched anything else like pistons, rings, bearings etc. Also my cam sheet says that I should let my 4k idle at 2000rpms for the first 60minutes is this more than necessary? As I being told 30 minutes would be efficient enough, thanks.

[altezzaclub]

I'd give it a week of general driving, so you know there are no niggling problems before you have it tuned. Don't thrash it in case its running lean with those jets and you burn a valve. That would also smooth the cam in, and I never ran mine for any particular time at 2000rpm when I fitted it.

 

How about tappet gap?? Are you gong to use the big gap that the cam grinders talk about? I think its 14thou on my Crow, so I started there but they were too noisy so I closed them down to an acceptable level. I've got them at 12-13thou using the 'rule of 9' method of setting and just one is tapping still.