31 replies to this topic

[austinmayfair85]

Hi everyone,

 

I am a first time engine builder seeking help on a couple of camshaft issues on a 998 rebuild.

 

1) Adjustable vernier sprocket fouling the triangular retaining plate bolts.

2) 0.3mm of camshaft float.

 

Pic 1 shows how the sprocket fouls the bolts once it's tightened up. Even with the excess float, I can't see how this setup would clear the bolt heads?

 

If I use a different duplex sprocket (non-adjustable) the sprocket clears the bolts easily. Am I experiencing a bad design issue?

 

With the sprocket fitted however, I am getting 0.3mm of float with it all torqued up. How can I remedy this to get it within spec? 

 

Any pointers much appreciated.

Attached Files

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[Ethel]

There are clearance issues putting duplex sprockets in the later timing covers designed to go ever chain tensioners, so it may be a deliberate attempt to reduce that. you will want some cam endfloat without the sprocket fitted: if there isn't any the cam will be creating side load in the oil pump. It's the triangle plate, between the cam & the sprocket that sets the true cam running clearance, so you need to be able to torque up the big nut on the cam end to see what it is - hopefully less than free play between the cam & pump. You could need different screws to hold the triangle plate in. You could grind down the heads if it's only 1 0r 2mm.

[nicklouse]

Fitted the crank sprocket and shimmed the camshaft sprocket yet?

[Ethel]

As above, there's more than the running clearance to consider. It could be getting the sprockets aligned suggests the best route to gaining  the clearance.

[austinmayfair85]

Thanks both.

I haven't been able to get the sprockets anywhere near ball park alignment. I think I may fit countersunk screws first and then go from there.

[nicklouse]

Nope.

you don’t need any there.

 

but what bolts/washers have you used? 

[PoolGuy]

If I use a different duplex sprocket (non-adjustable) the sprocket clears the bolts easily. Am I experiencing a bad design issue?

 

What make is the problem duplex?

[austinmayfair85]

If I use a different duplex sprocket (non-adjustable) the sprocket clears the bolts easily. Am I experiencing a bad design issue?

What make is the problem duplex?

It's a minispares unit

[m1n1]

I used button headed bolts on my engine with those minispares gears.   They are not as tall and worked for me!

 

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[austinmayfair85]

Thanks everyone for your help so far.

 

I have the gear on and torqued up (button head bolts worked a treat). But I am only getting 0.01mm of end float.

 

Where do I go from here? For comparison, the old triangle plate produces the same result.

[imack]

Is that with or without the oil pump being installed?

[austinmayfair85]

That's with the oil pump on.

 

I have refitted the old simplex gear and that produces only 0.03mm of end float too. This is with a new camshaft. I haven't got a previous measurement with the original cam for comparison. 

 

Is this a case of machining the cam sprocket to allow it to sit deeper in the triangle plate? 

[imack]

If it's not the oil pump that's causing the lack of end float (I'd have to remove the pump and re check it) then as you say, you need to machine the cam sprocket.
Not sure whether there's shims available for the cam sprocket. Obviously you need to shim the crank sprocket to align with the cam as well.
I had to machine my old Kent cams vernier pulley to give appropriate end float.

[austinmayfair85]

OK that's useful.

 

With the oil pump off I get 0.04mm of endfloat. Replacing the pump gasket I get 0.04mm too. 

 

So I guess take 0.03mm off the sprocket and go from there? 

[nicklouse]

Oil pump ca not effect the end float as there is no mechanical fixing. All it can do is stop the cam shaft move towards it.

 

the nature of the cam shaft pushes it away from the pump which is why you pull the cam away before setting your gears.