Cam Timing Incorrect

[ukkid35]

Now I've used Tanguero's TDC method it's really clear that the cam timing is totally FUBARed, which explains why it maxes out just under 170mph.

There's not enough adjustment within the sprocket slot allowance, so now I have to find a way to shift the cam chain one tooth at a time, with the timing cover in place and the engine in situ.

This is really going to be horribly difficult, or physically impossible. I am not looking forward to find out which.

There's very approximately one tooth's adjustment via the slot, so the chain needs to be on one of two teeth. Since it isn't, I need to jump the chain one tooth in the correct direction, and that is the issue I'm facing.

I'm vary wary of taking the sprocket off the cam without the retainer in place, but if there isn't enough slack in the chain then that is what I will have to do.

I guess as long as the cam is in a stable position and doesn't turn of its own accord, which it is when the end cams are on overlap (with 1.5mm diff), and as long as the other cam is stable as well, which is much more difficult to ascertain, then it should be OK.

TwinKam said:

First, get the cam where you want it and then 'walk' the sprocket around to a different position keeping the chain and the rest of the engine exactly where it is. you'll find that when you've moved it about 90 degrees, the slots will line up, aim to start with them roughly in the centre of the slots so that you have scope to go both ways.

So you think there is enough slack to do this with the sprocket in place?

If so that is very good news

[ukkid35]

Because I managed to set the cam timing so it is too far advanced, this could also explain the low rev knocking, which would be good news

http://victorylibrary.com/mopar/cam-adj-c.htm

[TwinKam]

Paul, I have no experience of doing it on the AJP (that pleasure is soon to come) rather I am talking in principle of timing other engines with 'vernier' pulleys.
I would mark everything up, crank and both cams to the block/heads and chain to sprockets (Tipex is your friend), wind off all chain tension.
Working on the odds bank you should now have enough slack to 'drop' (haha) the sprocket away from the chain and rotate it tooth by tooth until you reach an agreeable position. Trick is to keep enough tension upwards on the chain so that all the slack is around the sprocket and not lower down (although I don't think there is enough room beneath the crank sprocket for the chain to jump a tooth). By marking the cam sprocket to the chain, you will see how many teeth you have moved. Check you're right by putting the tension back on the refitted chain and sprocket.
If all good then remark the odds sprocket to the chain and move to the evens bank; this will be harder because you will need to get the slack over around that cam sprocket now, which will move the odds cam, hence the marking up of everything that you can return to correct tension and shaft positioning when you check the sprocket's new postion.
Finally, with everything nipped up and tension reinstated, rotate the engine a couple of times and check again that you still have adjustment leeway.
HTH
Rik

[ukkid35]

That could not have gone better.

This is the first time I've had any confidence that it's actually correct, so I am very excited that the pinking will be much reduced, and the performance will be back as well.

The way I used Tanguero's bubble film method was to apply fluid again when TDC was first identified, and then the film moves within the transparent tubing very quickly indeed (rather than outside as a bubble) and you can see the exact point when it reverses direction. With a total surface area of perhaps 50mm sq vs the area of the piston 6500mm sq, you can see how the magnification is a factor of at least 100.

I need not have been worried about moving the chain on the sprockets. Yes you need to keep your wits about you, and you must ensure that the bolts are not dropped down the timing cover, I use a telescopic pen magnet at all times to ensure that even if I slip they never get away. But the end result is that I reckon it is spot on for the first time ever.

[HarryW]

It's been years before I've even considered cam timing on the AJP, but I seem to recall there being two schools of thought, one even lift on the overlap and the other 1.5mm difference. Question is what is best and why....

[ukkid35]

HarryW said:

It's been years before I've even considered cam timing on the AJP, but I seem to recall there being two schools of thought, one even lift on the overlap and the other 1.5mm difference. Question is what is best and why....

I didn't actually measure the degree of retardation, but specifying level rather than 1.5mm, probably accounts for at least 10 degrees of retardation.

Whereas my inept cam timing (due to lack of precise TDC identification) was probably 10 degrees or more of advance from TVR spec.

To understand the consequences of advance vs retard then this really helped me (don't forget that the AJP8 is SOHC)

http://victorylibrary.com/mopar/cam-adj-c.htm

[Jhonno]

HarryW said:

It's been years before I've even considered cam timing on the AJP, but I seem to recall there being two schools of thought, one even lift on the overlap and the other 1.5mm difference. Question is what is best and why....

Iirc even lift was for better idle/bottom end, and 1.5mm was for power.

[julian64]

I have set my both ways, with the 1.5 and with level, and I can tell you on mine the sparkle seems better with the 1.5 so I stuck with that.

To set it I use the bottom of a modified micrometer. To set the TDC I use a screw in deadstop

I would echo the above comments that when you are doing it there is a lot of cam rotation between level and 1.5

Just as an aside Jules always used to say he set them level for better performance so I am tempted to retry at some point.

[ukkid35]

Well that was worth doing.

Engine Totally Transformed.

I'm sure part of that is due to freshly correct valve clearances, but most must be cam timing.

Engine has never run this well ever before, and this is just from a trip to fill up before tomorrow's drive up to Stamford for the Burghley House meet.

[Outl4w]

I love your threads, really informative. Most of it is well over my head, butI really like reading the work you do and appreciate all the detail you put in.

I will never attempt anything like this, but interesting to see how it all works.

Glad you are finally getting there with the jobs for the summer!!

Enjoy it mate!

J

[HarryW]

ukkid35 said:

Well that was worth doing.

Engine Totally Transformed.

I'm sure part of that is due to freshly correct valve clearances, but most must be cam timing.

Engine has never run this well ever before, and this is just from a trip to fill up before tomorrow's drive up to Stamford for the Burghley House meet.

I presuming that's with the uneven lift (+1.5mm). Was it even before? and does the lumpy 1700-2000rpm smooth out and the hole in torque around 3200 get better?

[ukkid35]

HarryW said:

I presuming that's with the uneven lift (+1.5mm). Was it even before? and does the lumpy 1700-2000rpm smooth out and the hole in torque around 3200 get better?

Yes now set to 1.5mm

But the comparison is with it being totally wrong, significantly advanced and not even from side to side.

It was probably so wrong that I was risking valve piston contact.

I can now accelerate from 30mph in fifth, which I would never have dreamed of attempting before.

Last time my GF came with me for a 300 mile round trip, she asked to put the radio on while we were still in town. I said no because I needed to be able to hear the engine to guard against pinking. That's how nervous I was about driving it off track. Only now is it really clear to me that I've working around this issue for so long that it became normal.

[ukkid35]

Outl4w said:

I love your threads, really informative. Most of it is well over my head, butI really like reading the work you do and appreciate all the detail you put in.

Thanks, I have benefited so much from the generosity of others that I feel obliged to pass on what I've learnt, even though it often makes me look quite inept!

In this case it was all about fixing a problem that I introduced because I failed to identify TDC correctly on each bank.

[HarryW]

I presume you used a hollowed out spark plug with a drinking straw tell tale using fairy liquid come leak detector fluid to measure the TDC rather than a DTI and welding rod down the bore...

[ukkid35]

HarryW said:

I presume you used a hollowed out spark plug with a drinking straw tell tale using fairy liquid come leak detector fluid to measure the TDC rather than a DTI and welding rod down the bore...

This was simply done with some clear tubing screwed in to the spark plug hole, and with a narrower piece of tube at the sighting end to magnify the effect.

The first time I did this nearly five years ago was with the heads off and finding the centre point between two marks I made on the flywheel with the piston halfway down the bore. But that was nowhere near as accurate and repeatable as the bubble/film method.

[julian64]

The trouble with the bubble ....method is that its exactly the same as the straw sparkplug method, Its trying to detect the top dead centre of the engine at a point where the piston is slowing down to stop, then moving very very slowly over TDC.
Its pretty inaccurate over maybe 10 degrees.

[ukkid35]

julian64 said:

The trouble with the bubble ....method is that its exactly the same as the straw sparkplug method, Its trying to detect the top dead centre of the engine at a point where the piston is slowing down to stop, then moving very very slowly over TDC.
Its pretty inaccurate over maybe 10 degrees.

That is what I had assumed to, I was totally wrong.

The film moves at quite a rate within the tube because of the magnifying effect and then reverses instantly without stopping.

[julian64]

ukkid35 said:

That is what I had assumed to, I was totally wrong.

The film moves at quite a rate within the tube because of the magnifying effect and then reverses instantly without stopping.

Sounds pretty good but its still looking at the smallest movement of the piston. dead stops look at the largest movement of the piston.and therefore reduce error. Problem with deadstops is that they take no account of the play in the engine.but you can pretty much gauge the play on the return swing.

I still think deadstops are easier though

[ukkid35]

My joy has been fairly short lived.

It's not because once the car became heatsoaked due to traffic, the pinking returned. I expected that, and it is so much better than before, so much smoother, easier and more relaxing to drive, that even though the pinking hasn't been completely banished, I am much happier.

Sort of...

One of the consequences of fixing the cam timing is the much improved torque, so I doubt it's pure co-incidence that an hour ago I lost 5th gear just 20 mins from Stamford.

Oh well, at least the car is driveable, but it's clear that I won't have the car ready for the drive to DN17 at the end of the month, not least because I'm away on holiday for two weeks over Easter.

Doh!

[spitfire4v8]

I don't know if the engine build manual was updated over time or whether the cam figures in there are from the first engine builds, but it's maybe noteworthy that the early engines were 4.2, clatter cam, small bore manifolds with a more pronounced reverse step and smaller engines exagerrate any inherent camminess in an engine. Also the early exhausts had an intermediate expansion box and right angle bends in the rear box rather than smooth bends .. the very first cerbs (ie first 6 months of production before all the dealer bulletin updates) made about 320bhp . Also they say if youre having to advance the cam a long way you're running too much cam in the first place .. Which is great if you unlock the breathing and put the cam back where it should be

Edited by spitfire4v8 on Sunday 9th April 11:03