27 replies to this topic

[scubaet]

Quick Question on Cam Timing

First the specs
Installing duplex double timing chain and a Kent 276 Megadyne Cam in 1293 A+

It is my understanding that the timing for the cam on a standard mini engine is at 106-107 degrees. The Kent camshaft should be advanced 3-4 degrees, so I should be setting the timing to equal 103 degrees.

When installing the timing gears you would normally align the dots on the timing chain gears to each other and then fine tune them. However when I did the below timing method it shows that my dots are 25 degrees apart. I've heard of a few degrees separation but is 25 degrees ok?



Method used to calculate degrees.
Find Top Dead Center on piston one.
Insert pushrod in second valve and place dial gauge on it.
Place camshaft timing degree wheel on crankshaft end, mark 0 or TDC.
Rotate crank forward until pushrod lift is at maximum.
Rotate crank each direction Take readings 5 degrees on either side of maximum valve lift.
Degree wheel read 110 degrees and 95 degrees.
Add numbers together 205 then divide by 2 = timing at 102.5 degrees.

Whew, that only took me 5 hours to figure out.

So do I trust the dots and my calculations are way off or, is this ok?

[GraemeC]

Are you using a dial guage to find TDC and max lift on camshaft?

[dklawson]

Just make sure you are measuring max lift on #1 intake valve, not exhaust. That's pushrod #2 from the front of the engine.

The dot-to-dot should be within a few degrees... certainly closer than 25.

[AndyMiniMad.]

Dot to dot should be fine for your cam....The way you have it in your picture is not correct. The only way to get a trully accurate cam time is to use Vernier adjustable duplex timing gear. Which you have not fitted...

Dot to dot will be near enough...

Here is a picture of when I did mine. These are set at 104.5 deg and the dots were still lined up. The only addjustabillity on these is the tiny bit you get when you loosen the allen bolts. No more than a couple of mm either way....So you can see how far out yours must be by the possition of the dots..

Edited by AndyMiniMad., 26 August 2011 - 01:48 PM.

[jaydee]

My 276 when installed was already at 106° with dot-dot alignment, that position is certainly not #1 cylinder TDC.
Kent comes with an installation with easy explanation about timing camashft in..

[ukcooper]

Dont know if video will help you.

[bmcecosse]

Don't waste time - set it dot to dot. It's what the cam is designed for. Any supposed 'benefit' from setting it a few degrees one way or the other will result in a 'loss' elsewhere.........ie Slight increase in top end power (used how often??) will be balanced by loss of tractability at lower revs.(used ALL the time). If it was an out and out 'racing' engine - it would be worth setting up cam timing - but obviously not with that cam anyway - and then only with repeated running at different settings on a rolling road to find the best setting.

[scubaet]

Thanks for all the fast replies, I actually used that video to do the setup, it looks like I may have something wrong. I'll post pics of how I took the readings in a couple of hours and maybe you can spot what I am doing wrong.

[bmcecosse]

Seriously - dot to dot and get on with it!!

[AndyMiniMad.]

Just watched that vidio....Do people still use Offset woodruff keys? And im with bmcecosse...Dot to dot for your cam is all you need..

Edited by AndyMiniMad., 26 August 2011 - 02:01 PM.

[GraemeC]

I'll beg to differ with bmceccosse on this one - I have previously fitted aftermarket cams with aftermatket timing gears that have proved to be over 7 degrees out.
OK there are two areas for innaccuracies to creep in here, but it proves that dot to dot isn't always perfect - especially on cams that have been reground.

If you have the equipment then do the job properly. However I think that video is quite poor - he doesn't exactly set TDC accurately!

And yes overset keys are still used - why buy expensive adjustable stuff for achieveing good valve timing on a well built road motor?

Edited by GraemeC, 26 August 2011 - 02:32 PM.

[AndyMiniMad.]

I'll beg to differ with bmceccosse on this one - I have previously fitted qaftermarket cams with aftermatket timing gears that have proved to be over 7 degrees out.
OK there are two areas for innaccuracies to creep in here, but it proves that dot to dot isn't always perfect - especially on cams that have been reground.

If you have the equipment then do the job properly. However I think that video is quite poor - he doesn't exactly set TDC accurately!

And yes overset keys are still used - why buy expensive adjustable stuff for achieveing good valve timing on a well built road motor?

I agree that dot to dot is not perfect....But for this cam it will be near enough...There will be no noticeable difference to the car by having it perfect.

And adjustable timing gear is my prefered option as its easyer to adjust than having to remove everything to change woodruff keys...But thats my personal choice...

[dklawson]

I am 100% with GraemeC. There are production variables on keyway positions in the cam, crank, and both sprockets. That can add up. For a street engine, dot-to-dot is certainly OK. If you are fitting anything other than a stock cam, it would be false economy to not at least check the cam timing. Once you have checked what you get with standard pulleys and dot-to-dot alignment, buy the offset Woodruff key that you need to put the timing where the cam maker says is best. The offset keys are a lot less expensive than buying a vernier timing pulley set.

[cooperrodeo]

You are turning the crank in the same direction each time, are you not? Personally I would take measurements much further out than 5 degrees as they are far more accurate than close to the peak of the cam. I certainly would not rely on an after-market cam being ground to be used with the dots. I have used offset woodruff keys but they are a bit expensive so I file my own.

Some years ago I was in contact with a very well known cam manufacturer about cam timing and the man told me I might have cosign (sic) errors. Since he could not spell the word correctly I don't think he knew what he was talking about. Maybe he only got an A* in GCSE maths.

[scubaet]

Ok, here are somewhat better photos.

Set piston 1 to top dead center. Note the cam dots are 25 degrees apart.



Fit Degree Wheel and set to 0.




Rotate crankshaft forward clockwise from the front (correct?)
Continue until pushrod 2 is at maximum lift. Set dial gauge to 0.




Rotate cam each direction 5 thousanths on the dial gauge and note degree wheel readings.





Add the two numbers, 95 + 110 = 205. then divide by 2 = 102.5

So using the gauge and wheel I am at the correct 103 degrees I wanted.

Now if I do the same measurements with the dots aligned, I get a reading of 127 degrees.

So am I measuring incorrectly?