Cerbera Manual - Valve clearance procedure

[Wolvesboy]

Hi All,
Having measured my 4.5's valves I definitely need to rub down/ replace some shims.

1) Please correct me if I'm wrong: the above Cerbera manual uses the cam timing on pages 19+ irrespective of TDC?

2) Why bother manually getting TDC (ie bubble method) if the cam is moved to the front overlap lobe position ---- again to check the rear lobes ---- then again for the "Safe" position?

3) What is this "safe" position? I'm presuming all of the lobes will be away from the buckets and therefore the cam can be easily placed back into position?

4) Upon replacing the cam it seems there is no reference point to use as the sprocket has been moved 1.5 teeth along!

5) I'm worried the chain will fall off the lower sprocket if the tensioner goes a little too far as well.

Talk about a faff! Unbelievable messing about.

[spitfire4v8]

The safe position is just a position where you can put the cam back in without damaging anything because it puts the pistons part way down the bore.
Forget the manual.
Accurately mark up the relationship between the cam flange and the drive sprocket and make sure it goes back exactly on that mark, that way the cam timing is the same as before (whether that is right or wrong, but at least it's the same).

[GT6k]

Even in the safe position there is still considerable tension in several of the springs. I bolt a bar across the centre of the cam (on long studs into the cover bolt holes) so that i can unload the tension in a controlled manner. I suspect that the cam release and refit procedure is the reason for some of the cam failures that have been seen in the past.

[Thunderroad]

GT6k said:

Even in the safe position there is still considerable tension in several of the springs. I bolt a bar across the centre of the cam (on long studs into the cover bolt holes) so that i can unload the tension in a controlled manner. I suspect that the cam release and refit procedure is the reason for some of the cam failures that have been seen in the past.

Thats a great idea, i hate removing/refitting the camshafts due to this, i will try that next time!
Thanks GT6k

[Wolvesboy]

Thanks fellas.

So --- am I correct that I get TDC for piston 1, mark up, then set the cam timing off the front lobes (ideally even)?

Get the rear cam lobes at even, then rotate the cam sprocket 1.5 teeth to get the "safe' position?

Anybody have any photos of measuring the cam lobe positions please? I've never used a DTi and the manual uses a solid bar!

Cheers.

[ukkid35]

WSM Section G said:

The camshaft may be rotated while the engine is in the 'safe' position in order to check valve clearances DO NOT rotate the crankshaft or damage will occur.

The only problem is there are no flats on the cam shaft to allow you to turn it easily with a spanner. Therefore I don't re-check the valve clearances without fully installing the sprocket with the scribe marks precisely aligned. Then I re-check after turning the crank. This takes longer, but I can't see an elegant way of turning the camshaft otherwise.

[Thunderroad]

ukkid35 said:

The only problem is there are no flats on the cam shaft to allow you to turn it easily with a spanner. Therefore I don't re-check the valve clearances without fully installing the sprocket with the scribe marks precisely aligned. Then I re-check after turning the crank. This takes longer, but I can't see an elegant way of turning the camshaft otherwise.

I use the grinding disc removal C spanner that came with my grinder, the two little lugs are at just the right distance apart to fit into the sprocket fixing holes on the camshaft flange, this gives enough leverage to turn the camshaft quite smoothly.

[Jhonno]

ukkid35 said:

WSM Section G said:

The camshaft may be rotated while the engine is in the 'safe' position in order to check valve clearances DO NOT rotate the crankshaft or damage will occur.

The only problem is there are no flats on the cam shaft to allow you to turn it easily with a spanner. Therefore I don't re-check the valve clearances without fully installing the sprocket with the scribe marks precisely aligned. Then I re-check after turning the crank. This takes longer, but I can't see an elegant way of turning the camshaft otherwise.

My cams have flats..

[Wolvesboy]

So just as good/tricky marking up and removing cam using TDC position without going to "safe" position? I think another bar across the cam to stop it springing up may be used.

Any photos anyone of tool used to check lobe for 1.5 gap or even positions?

Thanks

[Jhonno]

Thunderroad said:

GT6k said:

Even in the safe position there is still considerable tension in several of the springs. I bolt a bar across the centre of the cam (on long studs into the cover bolt holes) so that i can unload the tension in a controlled manner. I suspect that the cam release and refit procedure is the reason for some of the cam failures that have been seen in the past.

Thats a great idea, i hate removing/refitting the camshafts due to this, i will try that next time!
Thanks GT6k

Small even turns loading the camshaft up carefully works too..

[julian64]

Wolvesboy said:

So just as good/tricky marking up and removing cam using TDC position without going to "safe" position? I think another bar across the cam to stop it springing up may be used.

Any photos anyone of tool used to check lobe for 1.5 gap or even positions?

Thanks

I use a simple digital caliper. If you turn it upside down and use the bottom as a depth gauge. Mine just spans the gap. Very accurate

[Jhonno]

julian64 said:

Wolvesboy said:

So just as good/tricky marking up and removing cam using TDC position without going to "safe" position? I think another bar across the cam to stop it springing up may be used.

Any photos anyone of tool used to check lobe for 1.5 gap or even positions?

Thanks

I use a simple digital caliper. If you turn it upside down and use the bottom as a depth gauge. Mine just spans the gap. Very accurate

Or a straight face to check even.. (Which is now the accepted way to time them).

[Wolvesboy]

Thanks.

So easy to check level lobes then? - I didn't want to say just a visual as too easy to be shot down!

I have 6 inlet valves showing lees than optimal positions:

1 - 0.17mm 2 - 0.1mm. All the exhaust valves are 0.30mm!
3 - 0.2mm. 4 - 0.2mm
5 - 0.08mm 6 - 0.25mm ok
7 - closed/zero. 8 - 0.25mm ok

Obviously inlets 5 + 7 are pretty bad and could be easily contributing to my poor running/ chugging under load etc. I hope I can grind the shims down but no.7 is a worry as I don't want to mess about with valve stems etc.

Exhaust presently being crack repaired and I'm going to use ACT exhaust gaskets to ensure a proper seal.

Weather is picking up nicely here (sorry!) and cannot wait to see the results of all this plus my decats. Flames out of the exhaust please!

[ukkid35]

If you are going to take the shims down by hand, I suggest you check that they are still true if you remove more that say 0.10mm

Otherwise there is a risk that they would put undue stress on the valve stem and the bucket

If you choose to buy them and have them sent to you, make sure they are measured before they are shipped, as the usual supplier doesn't always have the right shims in the right boxes

[Rufus Roughcut]

https://www.pistonheads.com/gassing/topic.asp?h=0&...

I used a drill stand to ensure the shims were cut flat.

[julian64]

Be careful that the shims are unlikely to be anything more than case hardend. Likely therefore that multiple loss of surface is just going to cause them to be softer an softer. I wouldn't therefore make a big change to them. Or you could do what I did which is to file them down then harden them again

[Wolvesboy]

I’m sure I’ve read somewhere that the shims are through hardened?

[Jhonno]

Wolvesboy said:

I’m sure I’ve read somewhere that the shims are through hardened?

I have seen similar..

[Wolvesboy]

I think Ive got a problem or two. The exhausts are all good at 0.3 everywhere.

The shims for my inlets are already pretty thin:

Actual clearance (mm) Shim thickness (mm)
1 0.17 1.75

3 0.2 1.91

5 0.08 1.51

7 closed 1.53

2 0.17 1.52

4 0.2 2.54

6 0.25 okay

8 0.25 okay

I'm wondering what to do now. Does this mean new valves are needed?

[CerbWill]

The thinnest shim TVR Parts sell is 1.47mm so I'd seek advice from APM, Powers or Str8six if thinner shims than that are required.