Shimming Cam Towers

[RawlinSTR]

Hi all,

After removing the E88 cylinder head from the L26 engine I bought and finding that it had warped a considerable amount, I was generously donated a spare, which came out of a running car too.

I noticed that the fireface and valve cover face had been machined so I decided to measure the distance between the two surfaces to see how much had been taken off.

Its around 60thou, which is quite an extreme skim - as you can see from the below photos, the original casting marks have nearly been machined through:

I also think some work has been done on the combustion chambers to open them up a bit - I'm guessing to bring the compression ratio back down towards stock (standard E88 on left) - unless there are different types of E88 combustion chambers? It doesn't look like any work has been done on the ports.

Currently, there are no 'head saver' shims under the cam towers (which means it was previously run without them), however, from doing some reading, running the head without the shims will

1. Change the valve train geometry and most likely lead to me needing different size lash pads
2. Cause the chain tensioner to run dangerously close to its maximum displacement before popping out.

Both of these issues lead me to think that getting some head saver shims is the best way forwards - I will need a total of 20 (15thou each), 4 per cam tower.

I'm basically writing this post to check that my understanding of what needs doing is correct, and to see what those with experience of this kind of thing have to say.

Any advice is appreciated!

Thanks,
Simon

 

[jonbills]

As you say, 1.5mm skim would be a lot, but I'm not convinced by how you've measured it. There are indeed several variants of E88 so hasn't necessarily had porting work.
I'd be more inclined to measure the volume of the chambers to figure out what sort of a skim it's had.

Whatever it's had off it in total, I guess hard to know how much off each face.
If it hasn't had anything off the cam side then it won't change the cam/valve geometry. Adding tower shims definitely does.

Rather than buying tower shims and hoping for the best, I'd suggest taking it step by step.

Mock the head and cam up as is on the block and find out where the chain tensioner adjustment is.
Check out the wipe pattern on the rockers at cam and lash pad.
Maybe tensioner and wipe pattern will all be fine and you can just do it up.
If the tensioner is fine and the wipe pattern is off you need lash pads or possibly tower shims.

If the tensioner is out of adjustment then you need tower shims or one of the other tensioner solutions and then need to check the wipe pattern again. I took 1mm of the lower face of mine and it made the chamber volume 35.5

 

[RawlinSTR]

Thanks for the reply Jon.

You have highlighted some flaws in my thinking, you're right.

I can see visibly that both faces have been machined, but as you say I'd need to measure the volume of the chambers to have an idea of how much has been taken off each. To know how much off in total I compared the measured height (surface to surface) to production machined height (which I found on this forum).

I will follow the steps as you've said, they seem sensible. When you say "if the tensioner is out of adjustment", is that something I just check visually?

Simon

 

[jonbills]

I think what I'd do is assemble it and mark where the tensioner sits and then take the chain off and see how much more travel the tensioner has available.

The chains don't stretch very quickly so I don't think you need a huge amount of reserve with "classic car" mileage.

 

[RawlinSTR]

So I've mocked everything up and had a look at the tensioner, and it looks to me like it's too far out:

Something interesting to note as well is that the cam is advanced (the notch in the sprocket is to the right of the mark on the thrust-plate) with the chain assembled in exactly the same positions on the cam sprocket and crank sprocket as it was before disassembly (and obviously piston 1 at TDC firing):

Since this rebuild was originally supposed to be a quick gasket refresh, I hadn't gone to the effort of reading the 'How to Rebuild....' book (hindsight tells me I should've read it regardless, I know) so I didn't check the timing of the cam this way before disassembly, so I don't know if it was already advanced beforehand.

But logic says that since with a stretched timing chain, the cam would be retarded (notch to the left of the thrust-plate mark), then with a skimmed head, which gives the same effect as a stretched chain, the cam should be retarded in this case too.

Either way, with the chain tensioner as it is, I think I am going to need to shim the cam towers. Then I'll just have to ignore all the markers I put on the chain to be able to setup the engine the way it was before disassembly, and time the cam from scratch.

Once this is done I'll then have to check the wipe patterns to see if I need new lash pads (which will be more than likely..)

Again, this is just a post to confirm my thinking and make sure I haven't missed/ misunderstood anything.

Simon

 

[jonbills]

I use the kameari twin idler, so not a huge amount of recent experience with standard tensioner, but that looks to me like it's got a decent bit of extension left in it.
I'd check the wipe pattern before deciding anything. If the cam, towers and valves haven't been installed on this head before, also check the spring installed height. Getting the wipe pattern right can be quite a bit of work so if you don't need to do it, don't do it.
If you're worried about the tensioner popping off, you can make a sheet steel retainer, cribbing from this kameari one:
https://www.rhdjapan.com/kameari-l-type-adjustable-timing-chain-tensioner-l6.html


You're right in expecting chain stretch and skimming to retard cam, so with it showing advanced you are probably in sprocket position 2 or 3.
Its very close so wouldn't worry about it too much. You could try switching to a lower number position to compare?

 

[jonbills]

Although looking again, yeah, it's extended well past the guide.

 

[RawlinSTR]

Components I am swapping onto this head are the cam, rockers, pivots and lash pads - the towers, valves and valve springs were already on it.

The fact that the tensioner is extended well past the guide is what made me think it's definitely too far out, yeah. With it in the position it is in, it's able to lever up and down slightly which is not good and will lead to rapid wear on the shaft etc.

I really don't want to be doing the wipe pattern work because I can tell it would need a lot of time haha.

Oh I forgot to add in my previous post, the cam sprocket is in position 1, which is why I was surprised to see it advanced.

 

[jonbills]

I believe it's possible to slot the guide and tensioner bolt holes which would help rather.
You could get a Kameari twin idler. https://www.rhdjapan.com/kameari-l-type-twin-idler-gear-earl-s-blue-l6.html
Early Xmas present?
Or maybe accept defeat and get the tower shims [emoji16] and take it from there.

In terms of the advanced cam, I think you must be a tooth out if the bottom end really is TDC.
From memory a tooth is about 12 degrees. So retard the cam one tooth and advance it to position 3 would get you in the right place I reckon.
But that's all up for grabs again if you get the tower shims.