engine and drivetrain Head gasket conundrum

[MarkB]

I'm building a Ti engine, for my 2000cs. The compression is 9.5:1, it's a 121 head and the thickness is at the minimum, ie. it's had the maximum 0.5mm taken off.

I have a cutting ring head gasket, and a few questions on that:

1) What would my advantage be to use the cutting ring gasket? Is it recommended for this compression?

2) if i use the cutting ring gasket, and in the future need to pull the head, does the head need to be surfaced prior to using another head gasket?

3) if it does need to be surfaced beyond the max 0.5mm is that what the 1.80mm gasket as opposed to the 1.50mm thickness gasket is for?

Essentially I don't want to ruin my head by using this gasket if I need to remove it in the future.

On another note, I am thoroughly enjoying rebuilding the M10. It's been years since I rebuilt an M10 and it's such a beautiful engine to put together.

[Tommy]

I would recommend using the cutting ring gasket.

1. Main advantage being that then you probably don't need to pull the head.

2. It's not necessary. In racecars we use cutting ring gaskets and if the head is straight and surface is good the gasket (new of course) will hold at least couple assemblies without resurfacing. I can tell this by experience.

3. Yes I believe so, never used myself. But the minimum thickness is not "that" absolute value. It's where cam timing gets affected more (maybe too much) and of course CR is not in factory spec anymore but with adjustable cam sprocket the head is still usable even below the specified limit.

Tommy

[Anschauer]

If you want/need, I still have my pair of Solex 40 phh's I've kept since I junked my '66 1800 ti 40 years ago. Have manifolds, neck, etc. but only part of the linkage.

They last ran in my '73 back in '74, ate guibos and then I took them out and put them in the box.

nychart (at) hotmail dot com

[MarkB]

Thanks Tommy,

That helps, I'll use the cutting ring gasket. Not a conundrum as much as I thought.

best,

Mark

[Tommy]

You're welcome, I didn't understand the c...-word anyway :-)

Tommy

[MarkB]

Anschauer,

Thanks for the offer, but I'll be using some DCOE webbers. Post your carbs on the NK discussion, you might get some traction there.

[Mike87]

Just for reference, I am running an E12 head that is below the minimum thickness. I am also using an offset cam gear to compensate for the timing error. Stock head gasket too. At 80K+ miles it is still running strong.

[TobyB]

Frankly, don't worry much.

.5mm, as Tommy says, isn't the end of the cutting.

One thing- make sure the front cam chain cover's the same

thickness as the head, or you'll have to do silly things

with RTV to keep the oil in.

If it's not coming apart a lot, you can use the cutting ring gasket.

You don't NEED it- I run 11.5:1 with a standard gasket and a head cut more

than a mm. I do use a cam adjusting gear, but frankly, it's only to

correct for a few degrees.

Bigger problem in my mind is the lack of timing chain adjustment-

but up to a mm, you're fine.

One thing I would do if it was me- check the valve- to- piston clearance

before you bolt anything up. It's easy to do with a bit of clay and an

old head gasket, and it's worth real money for peace of mind.

Have at it- you'll be fine.

t

[MarkB]

Thanks Toby, I'm glad I asked. I didn't know about the adjustable Cam sprocket. Great info, and I will do the clay check before I tighten it up.

cheers

[john_a]

Thanks Toby, I'm glad I asked. I didn't know about the adjustable Cam sprocket. Great info, and I will do the clay check before I tighten it up.

cheers

As you check for piston-to-valve clearance, using a blob of modeling clay, there's good reason to expand your tests to get a fuller idea of how close things can be as circumstances change (i.e., adjustments on the cam sprocket.)

Do your initial checks with the cam timing set "straight up" or just as you plan to run it. With clay laid out on the valve pocket on top the piston, rotate the engine to leave an indentation on that clay from the valve.

Remove the head to check the clay, use a razor to slice the clay at the thinnest section, this will provide a better side view of how thick it remains (that thickness represents your piston-to-valve clearance.)

First time thru, perform this with a used head gasket and bolts tightened.

I also have a small notch cut in one edge of the old gasket, so I can confirm the compressed thickness of that gasket with feeler gauges (I did this mostly to confirm that ARP studs do not significantly change gasket crush.)

Once you know you have at least 0.057" clearance (which is the approx. installed thickness of the standard gasket) repeat the whole process with NO gasket in place (do not tighten the bolts fully without the gasket.)

Testing without the gasket will leave the clay that much thinner, which provides more accurate measure. And if you are OK without the gasket, there's no question you're in the clear when gasket is present.

If you have an adjustable cam sprocket, your next step should be to repeat the whole process to learn the impact of different degrees of valve timing adjustments on your piston-to-valve clearance. If you learn you are in danger with 6* advanced, then don't go there with the running engine. Better to determine this now, than to find out when the valves kiss the piston!

Last thing I like to do at this time, is to confirm the valve pocket on the piston is well located. I take an old M10 mech. fuel pump push rod (because it is 8 mm diameter & smooth sided) and turn a point on one end in the lathe. With the valve removed, insert this rod into the valve guide to mark the true center of the valve head on the piston top. Stock pistons probably are always OK, but don't trust any custom piston has the pocket centered just because you bought it from a BMW tuner.