How to check quench distance?

[Lazeum]

I'm in rebuilding process on my street L28 with P79 head.

 

Setup is as followed:

- F54 block, overbored to 0.30" (+0.75mm) & decked (unknown distance)

- stock Crankshaft machined on rod bearing to -0.25mm (if that matters)

- P79 head done by Braap with ARP headbolts, slightly milled down, port & polished with street Rebello cam

- Flat top pistons & stock L28 rods with ARP hardware

- All bearings, main & rods, are brand new

 

I'm currently checking distance to achieve correct quench on this motor. Since the deck has been machined, I've assembled everything on the bottom end to find out.

I end up with pistons popping up the deck surface at +0.53mm (0.021") - This has been measured, it is not a guess.

The plan is/was to use Felpro head gasket. This is how I found multiple answers that make me creating this thread. I've heard compressed thickness to be 0.40" (1mm), Braap has measured them at 0.045" (1.15mm). There're tons on info about this topic on hbz but there're also many answers that contradict each other (quench distance, headgasket thickness, etc.).

 

Pictures below show how I've measured deck height (it shows 0.49mm but I've been able to get 0.53mm afterwards)

 

 

Following also Bryan's (1 fast Z) advice and recommandation for quench, clearance between pistons & heaad should be in between 0.022" and 0.025" (i.e. 0.56mm to 0.63mm) to get the best of the quench.

The deal is with 0.040" gasket thickness, expected clearance will be 0.019" (0.48mm) - Engine will not work!!!!

BUT with 0.045" thickness, I end up being at 0.024" - I'm right where I would need to be!

 

So I'm trying to find a way to know for sure where I'm at. Since I found many contradictory information, I believe the only way to know would be to measure compressed gasket or piston/head clerance by myself on my engine.

I foresee many options:

 

- Install the head with and without the gasket and check some distances that would vary with the gasket. I believe this method would not be so reliable since a lot of variable can change from one trial to another.

 

- Put a shim on top of pistons around quench distance (i.e. 0.023"), install the head with gasket and see if I can rotate freely the engine without being blocked because of piston+shim+head clearance.

 

- Check gasket thickness with feeler gage once everything is installed - I would measure thickness but not where it matters at cylinders.

 

What would you recommend? I'm confused - one mistake on this parameters and I can start a new rebuild in a few & trash my head.

I then would need to find a way to correct quench distance. I've got 3 options in mind: get stock headgasket which seems to be thicker than Felpro gasket (1.25mm? I can see also 1.4mm?), mill the top of pistons to get the desire clearance or get a copper gasket at the desire thickness.

 

 

Please help!

 

 

 

Your source at Ross, being a sales rep/customer service rep, etc, for a custom piston manufacture, should know better than that. jmortensen summed it up rather well. If the Ross rep you are dealing with still insists such a thing is wrong, definitely ask for another rep/engineer that knows what he/she is talking about. Piston pop-up is fine so long as there are no mechanical compromises, i.e. rings getting to close to the deck etc.

 

Every N/A L-28 built after, (I think it was 8 of 1980 or there abouts, someone else here will have the exact manufacture date the change was made), any how, the engines with the P-79 head and flat top pistons, the pistons pop up OUT of the bore between .020†and .025†from the factory. So long as the head gasket is thick enough that there is approx .016†clearance between the cylinder head and the piston, all is well and in fact, quite good.

 

Here is an assembled short block with the OE flat top pistons, OE rods in an OE block, and the block was NOT decked. The piston pops up out of the bore .023"

 

Source => piston/deck height misinformation

 

First off, this post is NOT meant to discredit 1 fast Z in any manner. I hold Bryans work in high regard and would have no issues running one his cylinder heads or engines in my own personal Z car. At his young age, he has amassed a great deal of actual hands on experience building, machining and taking Datsun power plants to extremes that the rest of us only bench race about. Some feel he is abrasive, and yeah he can be sometimes, the point is, his work speaks for itself. He KNOWS what he is doing and talking about in regards to engine building, machining, and extracting power from the L-series.

 

With that said and the fact that I’ve haven’t measured any OE flat top piston "pop up" at any less than .019â€, it would seem that L-28’s in Arizona just aren’t as “pop-up†endowed as Oregon L-28’s. (Sorry, I couldn't resist that one).

 

In regards to piston pop up, (negative deck height), there are many factors that can and will affect piston deck height. Nissan machining consistency throughout the years was quite good, though machining tolerances such as crank pin offset, crank main line to deck height tolerances, etc can all affect deck height. Align honing a block, resizing the connecting rod big ends, offset grinding the crankpins, staggering bearings for fine tuning the bearing clearances, etc will also alter the piston deck height to some degree.

 

In all the flat top L-28 builds I have measured, I think .019†is the shortest I’ve measured though it may have been shorter, I just don’t recall. The norm I have seen seems to be between .020†and .025.†Pictured below is one such flat top L-28 currently in our shop that we degreed in the cam and now are machining valve relief’s in the piston tops. It is an F-54 block punched +1mm, L-28 rods, OE +1mm flat top pistons, Rusch Motorsports built MN-47 head with a Rebello .520†cam, triple Webers, FelPro head gasket. Rods have been resized with ARP bolts, Clevite bearings used throughout. Piston pop up measured “along†the wrist pin, on all 6 cylinders, at the front and rear of the piston, this engine measures a negative piston deck height of .0225â€-.0230â€. (Twenty two and a half thou to twenty three thou.)

 

So with a .023†negative deck height, and a .045†compressed head gasket, piston to head deck clearance for this particular flat top L-28 and MN-47 combo is .022†I have ran this combo on more than a few engines and it will leave the imprint of the pistons oversize on the squish portion of the head, but there is NO evidence of actual contact.

 

As Bryan eluded to, when you are building your engine, you either want squish, and all of it, or if you can’t acquire squish, you need more than .100†clearance between the top of the pistons and the chamber of the head. Between .050†and 100†is a nasty detonation zone. Between 050†and the .022†clearance that Bryan is talking about and the anti detonation tendencies of squish are realized and the benefits of added static compression can be realized.

Source => Best way to achieve piston to head clearance? (post #19)

 

Anything over 25 and you loosing, exponentially from there. 22-25 thou is perfect. Anything less than 22 is DANGEROUS. Pistons from the factory protrude out .016". Ive measured TONS of L series blocks, and never found a number more than this.

 

Raami, there are numerous posts regarding engine configuration, deck height, etc., etc. First thing you want to do is a lot of searching and reading. You'll want to investigate much more before coming to a choice of components and a final build plan. Plan to invest several hours reading and pen down lots of notes to yourself. Once you've done this your questions will become more specific and the assistance will be there for you. Your ideal clearance was mentioned above, between .016 and .025 will provide ample quench to reduce detonation.

[z-ya]

The stock clearance is somewhere in the 0.75 to 0.95mm range. With Felpro you will be around 0.5mm. I don't know how much L6 rods stretch at high RPMs. What will be the redline on this motor?

 

Basically you want to minimize the P to H clearance while accounting for rod stretch, and then add some padding. With a stock gasket (1.25mm) you will be safe for sure. This is what I would use.

 

Pete

[duragg]

Interesting reading here.

Is your front cover machined to match the milled block?

 

Squish and Quench; spending the rest of today reading up on this.

 

With the pistons already stabbed, seems like head gasket adjustment would be easiest. Why not sacrifice one in a press and measure the crush?

[Tony D]

I keep a used head gasket around for just this purpose.

 

"Clay the Head"

 

With the plugs out and a light coating of release agent (preservative oil) put middling clay on the head of each piston, assemble the engine, and rotate it through a full combustion cycle.

Remove the head and with a caliper you can then check valve clearance to piston, piston to head, and if you get fancy with a graduated beaker, combustion chamber volume.

 

If you at coming up shy right now, I would seriously consider taking 0.010 to 0.015" off the piston heads. This is the standard method on flat-top pistons.

 

Gives you a good excuse to keep a compressed (old used) head gasket hanging from a nail on the shed wall!

[Tony D]

Oh, stock Todd will stretch, but unless you are at 8000+ I'd not consider it much...

[Lazeum]

Thanks first for your support, I appreciate.

 

I've never thought about the front cover that indeed would not match my block I will have to check what I can do. Worst case scenario, I'll ask the machine shop to take care of it also. All my measurements tend to believe block has been milled by 0.10mm, maybe that's something I can deal with (sand paper, a flat piece of wood and perseverance)

Regarding the red line I expect to run, 6500 / 7000 rpm would be the max limit. With the help of Braap, we've designed the setup to be good with low end torque even if I sacrifice some hp in high rpm (Paul told me he achieved 267 crank hp on the dyno with 45DCOE and bottom end). So max hp would most likely occur around 6000rpm.

 

Then back to my question, I've done some tests today and I've got some conclusions

I have saved the previous used gasket which was fairly new so I've used it.

- First I've cut the gasket around the front cover area to give some free space to use a gauge to check head position back to the block.

- I've installed the head on the block with the old gasket. I zero'ed the position on the gauge.

- I then removed the head, the gasket and reinstalled the head without any gasket. It gives me the answer I was looking for (or kind of).

 

Felpro gasket changed head position by 0.87mm (0.034") so I definitively closer to 0.040" than 0.045" (too bad!)

The conclusion is quite clear: I cannot use the setup as it is right now without changing something.

Now I need to think about what to do, I think it will be quickly a matter of cost between new gasket (stock one at 1.25mm (0.060" 0.049") would be good with quench around 0.7mm - 0.027") or machining cost for pistons.

I'm however wondering how compressing twice the gasket could affect the measurement. would a new gasket compress that much also? The used on one in free state was around 1.25mm (0.060") in between bores whereas new unit is around 1.40mm (0.055"). Anyhow, I'm not going to take any chance with new one as is.

 

 

Since everything is already installed, new stock gasket would have also got my preference but don't forget I'm in Europe - it is not so easy to find parts for our Z's.

I wanted also to try the shim method on the piston but my shim kit was too long to fit & I did not want to sacrifice it (it is shaped for Rebello cam clearance on lash pad)

 

PS: Damn units!!!

Edited December 5, 2011 by Lazeum

[duragg]

 

I've never thought about the front cover that indeed would not match my block I will have to check what I can do.

 

On the last day of my F54 build I switched front covers for one that was in better shape, but must have come from a milled block; Tears of a clown. I didn't think to check and->Leaked stupid. The fix isn't pretty, but it no longer leaks.

[madkaw]

I have been reading this thread and not sure if you realize the error in your numbers

 

Now I need to think about what to do, I think it will be quickly a matter of cost between new gasket (stock one at 1.25mm (0.060") would be good with quench around 0.7mm - 0.027") or machining cost for pistons

 

 

isn't 1.25mm actually .049"

[Lazeum]

indeed, you're correct

1.25mm is 0.049 inch. As I said, Damn units!

[Lazeum]

On the last day of my F54 build I switched front covers for one that was in better shape, but must have come from a milled block; Tears of a clown. I didn't think to check and->Leaked stupid. The fix isn't pretty, but it no longer leaks.

 

One way it would leak like crazy. On my particular case, I would have been unable to assemble it without understanding what is happenning (and maybe damaging the head gasket...)

[didier]

One way it would leak like crazy. On my particular case, I would have been unable to assemble it without understanding what is happenning (and maybe damaging the head gasket...)

 

Hi, Matt

I think you have to look for copper gasket, uncompressible, and you'll be sure not to kill your pistons. many thickness avalaible,

 

it seems 0.27 ( 0.7 mm) is the right size for the quench, that's what i 'll put in mine, larger, and you loose the benefits anti-knock .

 

don't worry with the aluminium cover, 0.10 mm is not a problem with flat surface an sand paper, you can use loctite gasket joint and get no leak at all.

 

Tony was right with the clay test, you can also use chewing gum !!ah :!

[madkaw]

Hi, Matt

I think you have to look for copper gasket, uncompressible, and you'll be sure not to kill your pistons. many thickness avalaible,

 

it seems 0.27 ( 0.7 mm) is the right size for the quench, that's what i 'll put in mine, larger, and you loose the benefits anti-knock .

 

don't worry with the aluminium cover, 0.10 mm is not a problem with flat surface an sand paper, you can use loctite gasket joint and get no leak at all.

 

Tony was right with the clay test, you can also use chewing gum !!ah :!

 

I thought I was the only one that used chewing gum LOL. Actually I was trying to check for minimum piston/valve clearance and I used a stick of UNCHEWED Wrigleys(which measured about .095) and laid it in the piston. I was using a used/compressed head gasket and messing with cam timing and had to take the head off afterwards anyway, so I just laid a piece on the piston and lined it up with the valves. It actually worked because when I got the cam way out of time( wwaaayyyy retarded) the valve left marks on the gum. If someone was slick enough they could probably stick a piece(trimmed down) thru the sparkplug hole on an assembled engine.

[madkaw]

As far as headgasket thickness, when i disassembled my engine to change headgaskets, I meaasured the gasket thickness and it was .047. Unfortunetley I can't tell you what gasket this is, except that it came with a MSA gasket kit(i'm betting Felpro, but maybe original nissan).

I ordered a Nismo gasket from nissan and it is advertised as 1.25mm compressed. That would be dam close to what you need as far as numbers. Quench would be around .026 -not sure if you can get closer then that- and would you be absolutely sure of all your measurements? If the gasket compressed anymore then 1.25mm then you have a safety margin.

[z-ya]

Hi, Matt

I think you have to look for copper gasket, uncompressible, and you'll be sure not to kill your pistons. many thickness avalaible,

 

it seems 0.27 ( 0.7 mm) is the right size for the quench, that's what i 'll put in mine, larger, and you loose the benefits anti-knock .

 

don't worry with the aluminium cover, 0.10 mm is not a problem with flat surface an sand paper, you can use loctite gasket joint and get no leak at all.

 

Tony was right with the clay test, you can also use chewing gum !!ah :!

 

For a CR of around 9.0:1 (my estimate), a copper gasket might seal. I know with my 13:1 race motor, it couldn't hold the compression with ARP studs torqued to 60ft-lbs. You really need to machine with a groove for wire to get a copper gasket to seal under extreme conditions.

 

The compressed thickness of a stock gasket is pretty close to 1.25mm (maybe a few thousands under).

 

MLS gaskets are really expensive (~$300), and are made for big bore applications. And, there is not safety valve if you have a detonation problem and you don't detect it. A stock gasket will blow, saving your cast pistons.

 

Just use an OEM style gasket (~1.25mm). If you need help getting one to Europe, I can probably help you.

 

Pete

Edited December 5, 2011 by z-ya

[Lazeum]

I'm going to order a ishino gasket for the car. I found it on Amazon.

I've got a colleague who's travelling to MI this week, it is the right opportunity to request his help (he gladly proposed already to help). So I will go for it, I will skip shipping cost.

 

Pete, thanks a lot for your proposal. This is the kind of move that makes the hbz community a great one

Edited December 5, 2011 by Lazeum

[clarkspeed]

Good thread. I am in the middle of setting up a very tight piston to head clearance also. I have a set of .6, 1, 2mm used MLS gaskets on the shelf I pull down for mock ups. This time around I will be using a new 0.6 mm metal gasket since my pistons are at deck height or just slightly below.

 

As far as measuring, I found Tootsie Rolls work well for piston to valve and piston to head. I let them sit in the Florida sun for a few minutes to get little soft. After molding, quickly take them to the freezer for about 5 minutes. They have a unique characteristic that they don't expand or contract from the heat cycle. You can then cut into pie slices with a sharp knife as needed and apply the calipers. You have about 5 minutes to work before they start to get gooey again.

[Tony D]

Modeling clay doesn't require a freezer or sunny day.

 

And afterwards you can make little horsies and doggies for the shelves around the shop and tell everyone your kid did it...

 

Or so I'm told.

[z-ya]

Good thread. I am in the middle of setting up a very tight piston to head clearance also. I have a set of .6, 1, 2mm used MLS gaskets on the shelf I pull down for mock ups. This time around I will be using a new 0.6 mm metal gasket since my pistons are at deck height or just slightly below.

 

As far as measuring, I found Tootsie Rolls work well for piston to valve and piston to head. I let them sit in the Florida sun for a few minutes to get little soft. After molding, quickly take them to the freezer for about 5 minutes. They have a unique characteristic that they don't expand or contract from the heat cycle. You can then cut into pie slices with a sharp knife as needed and apply the calipers. You have about 5 minutes to work before they start to get gooey again.

 

I'm not sure if I would use those expensive MLS gaskets for mockup. I'd wait until final assembly to use the selected MLS gasket. You might be able to find precision shim washers to match the compressed thickness of the MLS gaskets to use for mockup. From what I have seen the HKS and Kameari MLS gasket advertised compressed thickness is pretty much dead on. Then of course check you valve timing and piston the valve clearance when doing the mockup.

Edited December 17, 2011 by z-ya

[clarkspeed]

Yea Tony, but you can't snack on the modeling clay while you are working!

 

I usually swap out the MLS gaskets after 4-5 "cycles" of installing and running so I have a few shop queens laying around. I have found they don't last forever if you do a lot of teardowns. We had one spring a leak last year after building and testing the engine in in sunny Florida, towing it to Atlanta and cranking it in 30 degree weather.

[Tony D]

You can't? Oh crap...