Cam Timing Pin Play, Enough To Throw Timing Out?

[M@tt 77]

I'm going to be fitting a catcam inlet cam to my Mi16 shortly along with a number 2 pulley and a PeterT offset woodruff key to get the timing spot one. However thinking about the whole cam timing issue has thrown up a few questions which i'm confusing mysefl with.

 

Using standard mi16 pulleys i usually just stick a drill bit through the timing hole into the cylinder head when replacing the cam belt but as you know this isn't a perfect fit due to the cylinder head an cam pulley oles being slightly differnet sizes, and due to the distance of the the pulley from the edge of the cylinder block this does allow a certain amount "rocking" back and forth of the pulley whilst it is is being held in place.

 

My question is with this ability to rock the cams and also depending on how you tighten the 2 tensioners is it possible that the cam timing isn't spot on and therefore possibly losing some power?

 

From a bit of reading up its obvious that cam timing out by a few degrees is enough to have an impact on power but will the distance that the cam is able to rock equate to a few degrees?

 

also using std cam pulleys will their realtive timing be kept constant due to the belt and teeth and so if the timing is out due to incorrect tensioner setting they will both be out by the same amount.

 

hope some of that makes sense, had a few beerss

[16v205 9]

Yeah it will advance/retard the timing slightly with the adjustent of the tensioners, but ive never measured how far out you can go with the belt at the correct tension. I would'nt have thought it would be possible to get several degrees out with the belt correctly adjusted, but this is why you turn the engine over by hand a few times and check the dowel positions again to make sure the timing is spot on.

 

If your using drill bits wrap some insulation tape around them to take the slack up in the dowel holes. Not perfect but much better than a sloppy fit.

 

Rich

[welshpug 1,657]

as long as the tension is correct and the timing pins go back in the holes straight it should be fine, maybe worth investing in timing pins?

 

I remember Paul ran my Mi16 on the rollers before a cambelt and it ran 143bhp and a LOT of torque, after a cambelt and me buying it its ran 160 bhp a few times (STD 2.0 in a 405!!))

[petert 586]

There is only a small adjustment possible from adjusting the tensioners, approx. 0.5 deg. camshaft. The offset key will move the lobe centre from 114 to 110 deg. with a #2 pulley. Add the 0.5 camshaft deg. and you're at approx. 109 deg. best. That's assuming the Catcam is ground with the key in the right relationship to the lobe centreline. I can guarantee my regrind cams to within 0.25 degrees. Who knows with a new cam? Ideally with the cam you have, you'd want the centreline at approx 107-108 degrees. I know Catcams say 110, but I don't agree with that. It gives up too much low-mid range torque.

 

The only way to confirm where your cam position, is to either measure the lift at TDC, or measure the lobe centreline. The later is very difficult in the car.

Edited March 6, 2008 by petert

[M@tt 77]

exellent cheers for the responses,

 

i'm getting the cam second hand fron Tidypug and Toddy has kindly donated some spare Peters woodruff keys, i think i might get/borrow some dial guages then to just check the lift at TDC then once i fit the cam.

 

should be fitting it in the next couple of weeks so will report back on the progress

[maxi 36 1 Cars]

You can always tell a quick mi a mile off.............the cambelt whines like hell! A tight belt makes for more power, sounds silly but its true! The over tensioning of it obviously alters the cam timing fractionally but it does make all the difference.

 

Maxi