12 replies to this topic

[087dave]

Hi all,
As the title says
Just interested what kind of results if fitted to time a hi-lift cam
And who produces the best set

Dave

[Cooperman]

I've seen everything from zero error to 8 degrees retarded when timing dot-to-dot. It's just tolerance build-up on a series of components with 4 different sources of possible adverse tolerance which can build up. That's why all modified engines need properly timed-in cams.

[Gr4h4m]

well to add. my Kent 266 was about 4 deg out. My piper re13t was bang on. 

 

I was told by my local rolling road that it was common for kent to need adjustment even when not using mini cams. They did say that Piper seem to be bang on or close to they key way when they have fitted them in the past. I tend to trust them as they have been more than honest with me in the past and my own experience seems to match...

[klivins]

My Kent 266 was spot on.

[KernowCooper]

My kent 276 is fitted with a offset key 4degs retarded dot to dot and once the chain stretches it worsens

[Cooperman]

It is not really the accuracy of the cam grind as that is but 1/4 of the error generating tolerances.

The manufacturing tolerances are:

 

Cam lobes to cam keyway

Cam sprocket keyway to sprocket teeth

Crankshaft journals to crankshaft keyway

Crankshaft sprocket keyway to sprocket teeth.

 

No machined component is absolutely accurate and if all four of the tolerances above are at maximum adverse condition the cam could be several degrees advanced or retarded, or, maybe, some of the tolerances will cancel the others out. I've even seen the opposing crank journals to be a degree out and with race cranks it is normal to get the stroking and indexing corrected by high-precision machining. My 'S' crank had to go down 0.010" from new for correction of stroke & index on all big end journals. 

 

It is so simple to set it correctly, why not do it properly after spending a lot of cash on a hopefully better engine?

 

The question is, do you want to trust to luck, or do you want to know it is correct? A camshaft 6 to 8 degrees out will definitely cost some bhp and/or torque.

[dklawson]

As above.  Set it dot-to-dot, run through several checks with a DTI and degree wheel and buy offset keys as necessary to get the timing right where it needs to be.  Offset keys are less expensive than adjustable sprockets but not so cheap that I would buy an assortment in advance.  Build, measure, buy an offset key if needed, then re-install the sprockets with that key.  Even if you are lucky and don't need an offset key, measuring the lift and using the degree wheel will give you confidence that everything is installed correctly.

[Cooperman]

I do wonder why, after buying lots of 'good bits' with lots of 'good money', some don't want to do the precise engineering necessary to get the best possible result, but just want to bolt it all together and hope for the best (and often get the worst!).

[Dusky]

I marked where my old cam was en put the new one in the same way( both 110 degrees)

[ado15]

I marked where my old cam was en put the new one in the same way( both 110 degrees)

 

But if they were reground cams, this still won't guarantee the same result. You still need to check with a DTI to ensure they are in the most appropriate place.

[Dusky]

Was a geniune new cam( rare i know)
Checked on view and it looks right to be honest

[Cooperman]

Most engine builders ALWAYS check with a 360 degree crankshaft protractor and a DTI to make sure is it correct to within 1 degree either way. I always set a new chain to 2 degrees advanced from nominal to allow for initial chain stretch and have found that after around 1500 to 2000 miles the timing is then absolutely spot on.

 

Do not skimp on engine build quality when doing it right is so easy.

[Gr4h4m]

A good chain is advisable...