Cam timing

I am setting up my cams, using a dial gauge.

Cylinder 1 comes up fine at 108 degrees (fully open inlet), but when I time up the other bank using cyliner 5 inletI am getting a reading of 139 degrees, where I would expect 108.

Am I missing something?

Or ! was the engine badly assembled by somone many moons ago, where they mis-set by 3 sprocket teeth on this bank (seems strange as the engine seemed to run fine)

Many thanks

sorry should have said - 2664cc un-even fire engine (a310)

That's too big a jump to be correct. It should be 105-110 degrees inlet full lift ATDC. 105 and 107 typical (different across banks on the odd-fire) You must measure TDC first using the gauge, then find full lift, and you must be sure to always be turning the engine clockwise. If you have to back off, back off a long way and go again from the same direction to take up andy slack.

Sussed it, I think, took dinner and wine to refresh the gray matter.

I was cam timing wrongly, not taking the un-even fire into consideration.

Can sombody confirm my thinking.

Was TDC'ing cylinder one then setting the cam to 108 on cylinder 1, correct I think, but then I was trying use the same TDC to measure the opposite bank on cylinder 5, not correct I think. When I 'TDC' 4, and use this as my reference for cam timing of cyliner 4 I come up with 108-109 good

Question now is ( and I should be able to work this out, but truth is dinner was with two bottles of wine) what is the the angular difference between the cylinders??

Hi stunned'

Good to see you on line! thought I was talking to myself!!!

Is my thinking right or wrong?

The 30 degrees difference you had corresponds to the fact that the evenfire requires rotating 120 degrees to time up and the oddfire 150 degrees, as stated in the workshop manual.

DG
Thanks, makes sense, apart from your assumption that I may have read the manual, I only read manuals when all else fails!!!

Okay, it's one of those really simple things that you do need to wrap your head around, and it took some serious brain-bending to get it strait in my mind so here goes.

The order at which pistons hit TDC is as follows:

415263

Ie top left to bottom right looking at the engine bay. If you think about how the pistons share a crankpin, obviously if something happens on the left bank first, the same thing happens on the right bank 90 degrees later (OR 60 degrees if it's an even-fire engine)

BUT

The firing order runs "backwards" up the engine from bottom left to top right as follows

635241

Trust me on this, the firing angles then drop out to be 150 / 90 on the odd fires, and 60 / 60 on the even fires.

So, regardless of phase, you know that if you're measuring the inlet valve full lift on number 6, for argument's sake (it's usually the easiest to get to) then you'll probably want to measure #3 on the other bank, and #3 follows on from #6 in 90 degrees (or 60 for an even fire).

But you have to keep track of where you are with your degree wheel because after finding TDC, you then rotate the crank to somwhere between 105 and 110 degrees to find valve full lift, meaning that when you're finished measuring the left bank, you need to turn the crank BACK by 15-20 degrees to get TDC #3. And my post above means you MUST turn it back past TDC then rotate forward to TDC to make sure all the slack is taken up in the same direction at all times.

Sheesh, it looks complex when I write it like that!

Martin

Stunned'
It's me Mark R (A310 with your cams).

Getting there, have rough measurement of 107.5/109 so as I was aiming for 108/108 think I will call that good enough 'for goverment work'

Think I have now got my head round the timing, but confused by one statement you make 'even fire is 60/60' should that not be 120/120?.

Cheers

Trust me on this, the firing angles then drop out to be 150 / 90 on the odd fires, and 60 / 60 on the even fires.

120/120, unless its a V12..

Now there is an idea, two uneven lumps joined together to have a 12 cylinder uneven lump, now shall I do it in W format or V??

Sorry, yes my mistake - firing angles are 120/120 but TDC's follow on at 60 degree intervals. ooopsie. and well done for those who spotted, you each win a bag of jelly beans.

Let m eknow how it goes Mark! althgouh I would persevere and get them the same. You can use any figure between 105 and 110. 105 more advanced seems to provoke more top end power but a bit gutless lower down whereas 110 makes for amazing throttle response and stoopid off-the-line accelleration but runs out of puff at top. I set the last set to 107 and for a road car it makes the most sense even if not the most powerful it's downright lovely to drive.Very peppy and civilised

Martin

[Alpineandy]

:D Now there is an idea, two uneven lumps joined together to have a 12 cylinder uneven lump, now shall I do it in W format or V??

An X 12.... I'm not sure how you'd keep the oil in the sump of the /\ though.

Andy, yes an X thats the answer, maybe I can build a special crank, with 4 cylinders running on each of the journals Oil, no worry,it won't run long enough to need any

[Alpineandy]

:not sure how you'd keep the oil in the sump of the /\ though.

a very big can of wd40 and lose all that heavy bhp sapping oil