Piston to deck clearance and head gaskets

[RPEVEHOUSE]

Hello all, I’m having g some trouble finding information on head gasket selection here in the forum. I’m new so that is probably the reason. At any rate, I wanted to ask a few questions about my piston to deck clearance and hopefully discuss the methods of checking said clearance. Also looking for info on head gasket selection based on these clearances. Ok, so I just got done checking my LLY block. It has Mahle cast race pistons with .075 pockets. The way I was taught on gas motors was to check the bottom and top crown areas while rocking the piston. Add the top to the bottom and decide by two. That would give the average potential for piston protrusion. That said, I have also heard of using a strait edge and feeler gages as well as simply using a drop indicator in one location on the piston. Which way would you guys lean towards being the most solid way of testing this?
On the subject of head gaskets based on the clearance I have just measured. Bank 1 top number was .0175 on cylinder #7 and Bank 2 top number was .0155 on cylinder #8. This would lead me to believe and correct me if I’m wrong on any of this. That a grade C Mahle wavestopper which measures 1.05mm or .0435 would allow a little more than .020 thou clearance on both banks which would be plenty. I’m not 100% sure what GMs spec is on this so if anyone knows, please share with me.
Well that about sums up what I’m looking to discuss and the questions I have. Feel free to comment and weigh in on any aspect of the task at hand and as always I greatly appreciate all of you. Thanks

 

[TheBac]

Jason helped me find this for you:

Head Gasket Question

GM lists 3 head gaskets for the LLY engine...... Grade A, B & C. What is the stock replacement? What is the difference? My parts guy isn't real helpful. Thanks, Lonnie

www.duramaxdiesels.com

 

[kidturbo]

A straight edge will get you close enough. With valve reliefs, about zero deck, stage 1 cam, running C gaskets, I spin two of these things 5800R's. Heads have been off a couple times, and no sign valves getting close. Math at time said we could run A gaskets, but have always ran C Mahle, so that what we roll with.

With pockets, you'd need a Big cam, and some above deck protrusion, before I'd break out the good measuring tools.

 

[RPEVEHOUSE]

A straight edge will get you close enough. With valve reliefs, about zero deck, stage 1 cam, running C gaskets, I spin two of these things 5800R's. Heads have been off a couple times, and no sign valves getting close. Math at time said we could run A gaskets, but have always ran C Mahle, so that what we roll with.

With pockets, you'd need a Big cam, and some above deck protrusion, before I'd break out the good measuring tools

Gonna be running g a Callie’s stage 2 camshaft. It requires .050 thou valve reliefs. I plan on checking my valve to piston clearance as well, just to be safe. I appreciate your help. Thanks

 

[RPEVEHOUSE]

Jason helped me find this for you:

Head Gasket Question

GM lists 3 head gaskets for the LLY engine...... Grade A, B & C. What is the stock replacement? What is the difference? My parts guy isn't real helpful. Thanks, Lonnie

www.duramaxdiesels.com

Awesome , I appreciate the link . I will read up on it when I get a few minutes. Thank you

 

[RPEVEHOUSE]

Jason helped me find this for you:

Head Gasket Question

GM lists 3 head gaskets for the LLY engine...... Grade A, B & C. What is the stock replacement? What is the difference? My parts guy isn't real helpful. Thanks, Lonnie

www.duramaxdiesels.com

Awesome , I appreciate the link . I will read up on it when I get a few minutes. Thank

A straight edge will get you close enough. With valve reliefs, about zero deck, stage 1 cam, running C gaskets, I spin two of these things 5800R's. Heads have been off a couple times, and no sign valves getting close. Math at time said we could run A gaskets, but have always ran C Mahle, so that what we roll with.

With pockets, you'd need a Big cam, and some above deck protrusion, before I'd break out the good measuring tools.

guess I should mention that the block was decked .005 as well as the heads being milled .005. I do have above deck protrusion but based on my measurements a grade C Mahle would be more than adequate

 

[Bdsankey]

Awesome , I appreciate the link . I will read up on it when I get a few minutes. Thank

guess I should mention that the block was decked .005 as well as the heads being milled .005. I do have above deck protrusion but based on my measurements a grade C Mahle would be more than adequate

Thankfully the head being milled has no effect on gasket thickness selection as long as proper valve recession spec was maintained.

This is the chart I've used for years. Thus far it still has been accurate (or at least never given or caused me any issues).

 

[RPEVEHOUSE]

Thankfully the head being milled has no effect on gasket thickness selection as long as proper valve recession spec was maintained.

This is the chart I've used for years. Thus far it still has been accurate (or at least never given or caused me any issues).
View attachment 134178

Thank you. This is the first time I have seen this particular chart. I appreciate your help

 

[RPEVEHOUSE]

Thankfully the head being milled has no effect on gasket thickness selection as long as proper valve recession spec was maintained.

This is the chart I've used for years. Thus far it still has been accurate (or at least never given or caused me any issues).
View attachment 134178

Going by this chart it looks like I would need the gaskets for the milled deck. That’s going by the way I have checked it with an indicator. What’s the chances you guys know where to get these particular gaskets? I know cosmetic makes some for decked locks but not sure if that’s for a duramax or not. Thanks

 

[RPEVEHOUSE]

Going by this chart it looks like I would need the gaskets for the milled deck. That’s going by the way I have checked it with an indicator. What’s the chances you guys know where to get these particular gaskets? I know cosmetic makes some for decked locks but not sure if that’s for a duramax or not. Thanks

I’m checking it by rocking the piston and measuring the top and bottom of the face of the piston. Adding those numbers and deciding by two. Bank one seems to be the worst with my largest number being .0175 and bank two at .0155. If you follow what I’m saying

 

[RPEVEHOUSE]

I’m checking it by rocking the piston and measuring the top and bottom of the face of the piston. Adding those numbers and deciding by two. Bank one seems to be the worst with my largest number being .0175 and bank two at .0155. If you follow what I’m saying

See my dilemma is this block was decked .005 and also bored .020 so none of the factory gaskets are gonna help me much I’m afraid.

 

[Bdsankey]

See my dilemma is this block was decked .005 and also bored .020 so none of the factory gaskets are gonna help me much I’m afraid.

0.020" overbore is a 4.075in (103.505mm) which does not need a different gasket. The standard gasket has a bore of 4.136in (105.05mm).

If your protrusion really is 0.0155" on one bank and 0.0175" on the other, Cometic and Victor Reinz offers a gasket in those thicknesses ranges. Cometic MLX have been a great gasket and my "go to" on the Cummins side. I've done a few sets of them on the GM side but nothing making power.

Cometic MLX is a 0.053" compressed thickness and roughly $195/gasket.

Victor Reinz is 0.047" compressed thickness and roughly $70/gasket.

 

[RPEVEHOUSE]

0.020" overbore is a 4.075in (103.505mm) which does not need a different gasket. The standard gasket has a bore of 4.136in (105.05mm).

If your protrusion really is 0.0155" on one bank and 0.0175" on the other, Cometic and Victor Reinz offers a gasket in those thicknesses ranges. Cometic MLX have been a great gasket and my "go to" on the Cummins side. I've done a few sets of them on the GM side but nothing making power.

Cometic MLX is a 0.053" compressed thickness and roughly $195/gasket.

Victor Reinz is 0.047" compressed thickness and roughly $70/gasket.

Thank you. That’s exactly what I was looking for.

 

[PureHybrid]

Measure the piston in line with the wrist pin bore. I've never bothered with a straight edge and feeler stock, too much human influence. Deck bridge and a dial indicator

 

[Chevy1925]

^^to add to that, rock the piston towards the front of the block and towards the back, record the number. Then move the indicator to the otherside of the piston over the wrist pin and repeat. The highest number is the one you base off of. I mark the top of each piston with that number. Not uncommon for one side of the piston to be slightly lower or higher than the other side.

 

[Chevy1925]

Iirc my latest built motor i ran .023-.025 piston to head clearance with grade A gaskets. I forget what protrusion was but it was low since the deck wasnt cut as much as expected. Either way, that was the p to h clearance i was shooting for, tight but still enough room for higher power

 

[RPEVEHOUSE]

Measure the piston in line with the wrist pin bore. I've never bothered with a straight edge and feeler stock, too much human influence. Deck bridge and a dial indicator

Thank you, can’t tell you how much I appreciate you guys. I was checking it on the outer and inner edges, not over the wrist pin bore. My thinking was what if the piston rocks. So that had me sweating bullets,lol. I will recheck everything tomorrow, over the wrist pin. I have 2 sets of Mahle Wave stoppers that I had planned on using on this build. I took a look at grade D gaskets from GM about 3 months ago and they were way over inflated as for as the price goes. Was hoping not to have to go that far. Like I was saying above, they only decked it .005. Just enough to clean the surface up. Heads were done the same way. At some point in the near future, I’m thinking I will probably replace the heads with some c c ported heads or something a little better than stock. As they sit, I have new Manton springs and retainers and will upgrade the pushrods and maybe the rocker shaft studs. Possibly the bridges as well. I got a pile of cash in the bottom end but I wanted to make sure this thing would hold up to anything I do as far as the air and fuel systems go. The only thing I did not do is the billet mains. Had a set from Wagler but couldn’t find a machine shop down here in the southeast that could cut them in. So I sold them on eBay. I am installing the Wagler girdle kit. I had the mains line honed with it installed and my bearing clearances were right on the money using HX bearings. All in all I think she’s gonna be a pretty stout engine when all is said and done. Again, Thank you all for the help

 

[PureHybrid]

If you ever get to where you need something thicker than a C gasket, shave some off the pistons. Most shops when they modify the bowls on an OE set they'll cut .010 off the top. And IIRC without looking at the catalog the Mahle pistons are available with a -.010 compression height

 

[Chevy1925]

Race cast come .010 off the top already, so with the deck down .005, you should be under stock spec by .005 for piston protrusion (or close to it).

Ill bet actual piston protrusion is closer to .010. Your probably going to want a thinner gasket, specially having valve reliefs

 

[RPEVEHOUSE]

If you ever get to where you need something thicker than a C gasket, shave some off the pistons. Most shops when they modify the bowls on an OE set they'll cut .010 off the top. And IIRC without looking at the catalog the Mahle pistons are available with a -.010 compression height

The pistons came from socal and were coated. So I was a little worried I would need to mill them. I have the capability just didn’t want to shave the coating unless absolutely necessary. I feel like when I remeasure I will most likely find my protrusion is a lot less than previously thought.