Need opinions.. Piston to head clearance..

TDIJetta99 · Dec 16, 2012

Currently building an ALH with 2.0 BHW pistons.. Measuring everything up with a compressed 3 hole BHW gasket I only have .568mm (.022") clearance from head to piston.. A 3 hole ALH gasket would get me another .1mm (.004") but the pistons are too big to fit through an ALH gasket.. I have about the same clearance from valve to piston after removing .040" from the valve pockets.. I'm using solid lifters and clay to measure everything up..

Do y'all think .022" is enough or should I take some material off the piston tops? I know I have to take out a little more from the valve reliefs, just wondering what everyone's opinions are about the clearance from piston to head..

Fix_Until_Broke · Dec 16, 2012

I think you're fine...I've got ~0.016" and so far so good. I don't know how far you can go, but this is where I'm at for 15k miles.

The pistion will grow ~0.010" from room temp to operating temp at full power. I'm assuming that the block and rods grow similarly so the net is just the piston expansion + rod stretch from RPM's on the exhaust stroke.

http://forums.tdiclub.com/showpost.php?p=3682956&postcount=225

Posts 207, 225 & 255 sum it up

0.051" piston protrusion and 0.0673" head gasket thickness gives 0.016"ish clearance

TDIJetta99 · Dec 16, 2012

I suppose it's about the same as stock piston to head clearance which is ~.5mm..

I took enough out of the valve pockets so with a solid lifter I have .060" space on the intake valve and .070 on the exhaust.. That should leave a little room for high rpm..

The only thing that concerns me about the pistons is towards the outer edge of the valve pockets the aluminum gets pretty thin near the edge of the piston.. I notice on the ASV pistons the valve relief pockets are ground right off the edge of the piston.. Any insight as to why? I can see that eliminating the small thin strip of aluminum that might get melted off in an extreme operating environment..

JFettig · Dec 16, 2012

Why not machine the tops of the pistons back the distance you need to be comfortable?

TDIJetta99 · Dec 16, 2012

I was thinking of knocking .010" off the top of all 4, just wanted some other opinions to see if I'm crazy or not.. If the BHW 3 hole gasket was as thick as an ALH 3 hole it wouldn't have been an issue..

Whitbread · Dec 16, 2012

I'd chuck the pistons in a lathe an knock .005-.008" off the tops to give you a little fudge room. Way better safe than sorry.

I'd also take the edges of the valve reliefs out like ASV's have from the factory. This is a crafter piston I did for a big valve headed ALH. I massaged the sharp edges with a cartridge roll after the pic.

TDIJetta99 · Dec 16, 2012

A lathe is going to be one of my next investments LOL... I'm going to end up running out of room in my basement real quick LOL..

I ended up making the valve pockets almost 1/8" deep to get .060 clearance with the monster cam.. I had almost 40 crankshaft degrees of interference before I messed with the pistons..

Whitbread · Dec 16, 2012

TDIJetta99 said:
A lathe is going to be one of my next investments LOL... I'm going to end up running out of room in my basement real quick LOL..

I ended up making the valve pockets almost 1/8" deep to get .060 clearance with the monster cam.. I had almost 40 crankshaft degrees of interference before I messed with the pistons..

And Eric was questioning if the new cam was "big" enough LOL

loudspl · Dec 16, 2012

Whitbread said:
And Eric was questioning if the new cam was "big" enough LOL

haha

i'm guessing it will breathe a little better

can't wait to see what it does on the bottle. it was pretty nuts before

v8 coupe · Dec 17, 2012

why can't you just make a thicker gasket? This is my plan if I run into issues with my build. I'll then shim the injectors closer.

TDIJetta99 · Dec 17, 2012

Do you have a part number for a thicker BHW gasket? 1.61mm is the thickest available I can find for an 8V 2.0L bore size..

edit: I see you said make one.. I might be able to pull that off.. one more layer of steel mixced in should make it thick enough..

Fix_Until_Broke · Dec 17, 2012

In theory, you want as little squish as you can get without having the pistons touch the heads so I like to run it nice and tight to get the most air in the bowl as possible.

I'd be interested in what is available besides machining pistions to deal with this.

I started a thread about it...a few months ago

brum · Dec 18, 2012

Shorter rods. I think somebody wrote that he'll be working on 0.5mm shorter rods. With them you can trim the block and get the correct piston protrusion.

Are the 1st repair size pistons shorter than the stock 2.0L pistons? If so - you can use them, but this will require reboring.

TDIJetta99 · Dec 18, 2012

Ya none of that is an option.. $650 for another set of rods and $1200 for another set of BHW pistons, not to mention another few hundred in machine work.. Not a chance.. Shaving .010" off the top of the current pistons is the most cost effective option and doesn't pose ANY sort of reliability risk.. I'm going to finish the valve pockets of all 4 pistons and assemble them all and re-measure my clearance and re-evaluate.. .5mm is a little tight, but that's about where they are from the factory and they don't hit the head with the weak stock rods at 6000rpm so they should be fine.. i have about 1mm of room at the closest with the valves so it's definitely good there..

Fix_Until_Broke · Dec 18, 2012

It was shocking to me how much removing a little material from the pistions or even sinking the valves deeper in the head changed the compression ratio. Simply dropping the valves 0.015" deeper in the head lowers the CR by ~0.5 point. Each 0.001" of piston protrusion/squish changes CR by ~0.1 point (assuming whole piston area). Taking 0.010" off the tops will not lower it by 1 point because you're not moving the valve reliefs or bowl area up.

I'm not sure what CR you're targeting, but it sounds like you've removed a lot of material from the pistons. I was targeting 18.5:1 and ended up at 17.5:1 and I didn't machine the pistons at all and have a tight squish.

TDIJetta99 · Dec 18, 2012

The primary goal is to get the engine to rotate without parts touching each other at high rpm with a camshaft that has a touch more than 11mm of lift and kind of long duration.. We'll worry about CR later..

I still have to take the sharp edges off, but here's what I have so far..

v8 coupe · Dec 18, 2012

Is this for the "monster cam"?

TDIJetta99 · Dec 18, 2012

Yes.. It has about the same lift as the Tdimeister cam, but there's a LOT more piston to valve interference so I'm assuming the duration is longer.. My engine only needed the valve reliefs knocked down to .055".. These ended up at .114" depth.. Stock valve reliefs are .030"..

v8 coupe · Dec 18, 2012

well if this is the one matt has it has .475"/.438" lift. at least assuming he is using the same specs I originally used! Glad to hear I'm not the only one that settled on ~.120" deep pockets.

TDIJetta99 · Dec 18, 2012

I think this one is a single pattern but I haven't measured the lift to be sure.. This is the second non-OE camshaft I've ever bought in my entire life that hasn't come with a cam card.. I've purchased hundreds of camshafts over the years too..

v8 coupe · Dec 18, 2012

well that's interesting. My Original monster cam had dual patterns a wider lobe separation and more lift then anything I could find. Specs for it were .475"/.438" and roughly 272/268 or something around there.

I based the cam on a combo of 8v turbo cam builds, large cummins options, flow bench work, and personal experience. based on your valve depths I'd say this cam is close to it. Also my design had a reduced base circle to help with clearance on the back side and to work with the longer valves I'm running.

TDIJetta99 · Dec 18, 2012

I'm 95% sure this cam has a large base circle.. That's one of the things I'll be measuring too..

Whitbread · Dec 18, 2012

TDIJetta99 said:
I think this one is a single pattern but I haven't measured the lift to be sure.. This is the second non-OE camshaft I've ever bought in my entire life that hasn't come with a cam card.. I've purchased hundreds of camshafts over the years too..

Actually, the cam card is sitting at my shop, found it a couple of nights ago digging through paperwork. It was in with the Colt invoices......so that's my bad

. I gave the full specs to Eric and they're posted on here anyway.

http://forums.tdiclub.com/showpost.php?p=3968211&postcount=77

v8 coupe · Dec 18, 2012

Interested to see how this works.

greengeeker · Dec 19, 2012

TDIJetta99 said:

I love seeing tdi parts on countertops next to food.

TDIJetta99 · Dec 19, 2012

haha yes the butcher block is a nice well lit area for taking parts pictures

TDIJetta99 · Dec 19, 2012

Whitbread said:
Actually, the cam card is sitting at my shop, found it a couple of nights ago digging through paperwork. It was in with the Colt invoices......so that's my bad . I gave the full specs to Eric and they're posted on here anyway.

http://forums.tdiclub.com/showpost.php?p=3968211&postcount=77

That's some of the info, but you know what a cam card looks like..

something like this

Fix_Until_Broke · Dec 19, 2012

TDIJetta99 said:
That's some of the info, but you know what a cam card looks like..
something like this

OMG - I can't believe you let that sacred information out to the public!!! You don't really need that information, trust us, Stage X is the best cam for you, it's just better, why do you want specs on it? Now everyone will steal it and there will be copies everywhere. Oh the horror!!!

A5INKY · Dec 19, 2012

fix_until_broke said:
omg - i can't believe you let that sacred information out to the public!!! You don't really need that information, trust us, stage x is the best cam for you, it's just better, why do you want specs on it? Now everyone will steal it and there will be copies everywhere. Oh the horror!!!

rotflmfao!

TDIJetta99 · Dec 19, 2012

hahaha funny stuff..

Need opinions.. Piston to head clearance..

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