ALH piston protrusion, fresh rebuild

I just got my block back from the machine shop. I am running oversized pistons with rosten rods. I had the machine shop measure piston protrusion for me so I could order the gasket when I got it back. So the block is now in my possession and I was given a measurement of .030” of piston protrusion. The reason for this lower number is the fact that the oversized pistons have a smaller height, and the block was in good condition so the machinist didn’t deck the block.

My question is do I need to deck the block to get within volkswagens .0358 spec for a 1 hole gasket or will I be ok with running a 1 hole gasket without decking the head. The block is already put together and I’m hoping I don’t have to take it all apart again.

Thanks

You should be fine with the 1 hole gasket. I assume the pistons your chose are a lower CR variety anyway, and you will be running more than stock boost when done.

They are ASV pistons from nural.

.5mm over stock


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Just went thru this myself. Rosten rods and a different piston. It took a lot of digging but this is what I came up with.

ALH gaskets are 1.55mm/1.63mm/1.71mm

BEW gaskets are 1.45mm/1.53mm/1.61mm

Gaskets are 0.08mm different

I did not want to lower my CR, or take the engine apart, so I went with the BEW 1.45mm (one hole) gasket. This brought my CR back into VW spec.

Someone else's quote;

Every 0.001" of piston protrusion is worth ~0.1 points of compression (roughly). If you had the correct piston protrusion for a 2 hole gasket and put a 3 hole gasket in, you will have added ~0.005" of head gasket thickness (or reduced piston protrusion relative to the head surface by 0.005") which will reduce your static compression ratio by ~0.5 points, from 19.5:1 nominal to 19.0:1 with the thicker head gasket.

skootyskoo

My protrusion was .033. Which is much closer than yours. My concern would be with having enough CR for starting.

Just noticed you were looking for VW Gurus, so disregard anything I said.

Anybody with experience with this would be a guru in my opinion.

How does the car run with the new one hole gasket?

With the one hole BEW gasket that should put me back in spec

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Runs good. No issues.

You can have low(er) compression and not have any starting issues. You can also do some changes in software to aid in starting, the tuners can help with that. Things like a more aggressive preglow strategy and pump timing and fueling at startup.

There are heavily modded ALHs that have a 17:1 CR and have no issues starting. The newer commonrail diesels have pretty low CR already. They just have better glow systems and better cold start strategies.

chuckthemech said:

Just went thru this myself. Rosten rods and a different piston. It took a lot of digging but this is what I came up with.

ALH gaskets are 1.55mm/1.63mm/1.71mm

BEW gaskets are 1.45mm/1.53mm/1.61mm

Click to expand...

I run the BEW gasket in my ALH, mainly because the stackup of the MLS was better, it's like 4,5, or 6 layers of wavy plates rather than the ALH two wavy plates, 1 or 2 spacer shims, and a thick shim plate
Means there's more spring force in the wavy bits because they're all nested, might seal better under severe abuse

adjusting your initial injection timing to a couple degrees advanced (and editing the timing maps so they won't call for anything ATDC so it doesn't set codes) as well as increasing the violence of the starting maps will make it light off just fine.

From some more research it seems the BEW is 1.49 and the BHW is actually 1.45.

Can I run the BHW even though I didn’t punch it out to 2.0?


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You might be able to use the BHW head gasket that’s made to use on an ALH block. I don’t think the stock BHW gasket will match up. It’s so common to bore the ALH to a 2.0 that aftermarket makes a head gasket just for it. Thats what I used on my ALH.

Victor Reinz part number 61-34250-00 is 1.45 mm thick and 81 mm bore diameter. That's a right gasket for you.

Darkside has the measurement to each head gasket on their site. By the way I’m 99% sure you cannot deck or shave a alh head due to it not having combustion chambers.

Yourbuddysatin said:

Darkside has the measurement to each head gasket on their site. By the way I’m 99% sure you cannot deck or shave a alh head due to it not having combustion chambers.

Click to expand...

Just noticed this, thank you. 1.45 gasket should get me to about where I need to be.

The car doesn’t see any cold weather, but I might have some extra fuel injected during starts.


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Skootyskoo,

My first issue you are not decking the block... I rarely find the block dead flat. If I am going to build for power, I have to start with flat cylinder head and block, to name just two components.

Just to dispel a generally conceived notion, just because you can pinch a .001" feeler between the block and a straight edge, does not necessarily mean everything is ok.
My technique for 'flat' on a block is to lay a machinist block across the webs between cylinders and lay the block over the bolts holes in line with the web at the sides of the block. If you shine a light behind the machinists block, laid on edge, and see light, the cylinder web is low compared to the outside edge of the block. Unless you have very high-end equipment, you otherwise, can't see it properly. Laser holographic imaging, we don't have in the shop.

Further, if you take a bastard file and strike across the head and do not touch the webs of the cylinders, again, the block is showing it is not flat. So, all this talk about which head gasket thickness is immaterial, if you end up going big power and blow the head gasket due to several thousandths gap between cylinder head and block.

To justify my position, whenever we set up to surface a block, many times we aren't interested in changing the piston projection height. That measure is made at the web between cylinders. There are times we deck the block and remove .002"-.005" from either side of the block to reach the point that we TOUCH the web. The reason this happens is the block tends to deform from head bolt tension and heat, making either side of the block deform and ride high compared to the centerline of the block. The webs become the 'valley' in the flat of the block.

As a contrast, the cylinder head,, especially when over-heated, tends to bow lengthwise. So, the two opposite deformations tend to cause the cylinder head gasket to blow between #2 and #3 cylinders, towards the manifold side. Our job when working to mate head and block is to eliminate, or at least minimize that condition.

Markus L., I don't think that is correct information. The BHW piston is 81mm STD, where the ASV is 79.5mm STD. Missing the cylinder bore to head by 1mm does not seem appropriate to me. The stock ALH head gaskets work perfectly with a +.5mm piston. Although I will admit, we alter the head gasket to improve PCP in other ways, I think getting the head gasket to match the bore closely is a very good idea.

I do not know of an aftermarket head gasket to adapt the ALH to an 81mm piston. It's unnecessary. The shape and dimensions of the ALH and the BHW cylinder head are identical. We use the BHW head gasket with BHW pistons in an ALH block.

The AHU on the other hand, we use the 2.0 gasoline head gasket, as the shape for both AHU and the gasoline engines are alike. The problem is the gasoline head gasket has only one size, so we must mill pistons and/or block to match the head gasket for proper projection.

When setting projection, It has always been my assertion that the best scenario is to create as much compression directed into the combustion chamber. Lowering compression by creating space between the piston and head is an inefficient burn. Increasing valve relief depth disturbs swirl chamber effect. It's a can of worms going there.

Franko6, You don't think it's appropriate to use 81 mm bore hg with 80 mm pistons but still use BHW hg (which has 82 mm bore) with 81 mm pistons. Ok.

Alright. I should change my statement to read, "..an additional 1mm gap". If the ALH/ BEW gasket fits a 79.5 or 80mm piston, why would you need to go with a larger and, by the way, more expensive BHW gasket? I realize we can still use the BHW head gasket and have no issue installing a 81.5mm piston.

Is there some good reason you would want to create that extra gap for a smaller piston? I suppose in the long run, the BHW gasket won't make any appreciable difference. Give it a few hundred miles and the gap will be plugged with soot.

Is there anything else you disagree with from my initial statements above?

The gasket I suggested has 81 mm bore diameter. It's for PD engines and meant to be used with 79.5 mm cylinder bore (for example BEW). It's not BHW gasket.

I see. I checked through my supply of ALH and PD head gaskets.

Checking h.g. bore size against an 81mm piston, an ALH is about 80mm, the clearance in the BEW is 81. The BHW is a larger hole, about 82mm. I stand corrected.

Just as Chuckthemech, this issue recently came up with a customer with almost exactly the same issue. It's a simple cure and I'm glad I questioned this. Thank you, Markus L. The piston height is improved by .1mm or almost .004". My customer will be happy to know this information. So am I.