4 replies to this topic

[MrBounce]

I hope you can help me. Am having a great time building up my engine using AndyMiniMad's guide ( http://www.theminifo...building/page-2 )

- I have just put in my camshaft and have timed it dot-to-dot. It's a Minispares Evolution 001 so it is a bit spicy in comparison to a standard 1275 cam.

I wanted to make sure the timing is as accurate as I can get so I am following his DTI timing teachings. All has gone well up until the point I get to maximum lift on No1 inlet pushrod. He says to turn the crank backwards after zeroing the DTI at max lift until it reads 0.025" (a pretty small amount) but does this mean -0.025" from zero? It's not entirely clear. He then says to move the crank forwards again to 0.005". Trouble is I can't get a reading at all past 0 when I turn the crank forwards. Should it be 0.005" less than -0.025" (so -0.020") or am I just doing something ridiculous thick here and just not getting it? And where do the 0.025" & 0.005" figures come from? I am confused and am convinced I am doing something wrong...

I reckon my engine will be "ok" at dot to dot but I would like to be sure. I have e-mailed Andy but he hasn't been on the forum since January so any help gratefully received

 

[dklawson]

I have not seen his guide so my comments are only based on your text.  As a quick sidebar, you must develop an understanding of what you are trying to do.  Both the cam and the piston will have periods of "dwell" where they sit at the top.  The crank will rotate through some number of degrees of rotation while this dwell is happening.   The measurements you take each side of "zero" with the DTI allow you to mathematically determine where the average (mid-point) of the dwell is... to accurately locate when things are at the very top.

 

Your initial understanding is correct that you turn the engine back then forwards again after zeroing the indicator at max lift.  However, I suspect you may have misinterpreted "zeroing".  You have found the point where intake number 1 reaches max lift.  Great.  Do not take the DTI and completely "unload it".  Make sure the DTI's measurement plunger is pushed in through about half its travel.  Look at the small needle on the gauge face and make sure it has moved through about half its range.  Then turn the outer ring until zero lines up with the long needle.  (Small needle near its mid-scale value, the outer ring zeroed to the big needle.  Do not zero both needles on the DTI).

 

In your subsequent work only watch the big needle that sweeps the face.  Turn the crank back as you watch the indicator. Stop at 0.025" DOWN from zero, then start turning forward.  Stop at 0.005" below zero and write down your degree wheel value.  Continue turning forward.  The indicator will go up to zero, then drop down again.  Stop when it reaches 0.005" below zero and take your second degree wheel reading.

 

The initial 0.025" rotation is to make sure you have turned "far enough" counterclockwise that when you start turning clockwise again you take all the slack and backlash out of the timing chain and pulleys.  0.025" is not critical and only required when turning backwards.  The values that are important are the 0.005" stopping points each side of zero (max lift).

[MrBounce]

Doug this makes a lot more sense now. I will head out to the garage tomorrow morning to try this out and will report back. Many thanks!

[MrBounce]

Doug - that was great advice. I will open a beer and raise it to you this evening!

[Spiffingly Good]

Bit of a thread revival but came up in my search, What was tyhe dot to dot timing like on the evo 1 cam Mrbounce? and have you noticed a tapperty noise from the engine once completed and running?

 

We have the same cam fitted into a 1275 but was never timed, but now have purchased a set of vernier gears and was about to undertake this.