SOHC head gasket thickness?

[Jeff Stich]

I have a PBS BVH head that I picked up a while back, & I'm thinking of putting it on a future-build 1500 block for my 128. Unfortunately, the head looks to have been skimmed a) more than once, or b) one time very heavily (the USA-type 1.5mm-deep machined recess surrounding the combustion chamber looks VERY shallow now - maybe .5mm to .75mm deep?). I'm hoping I can regain at least some of the lost head thickness by using an extra-thick head gasket, which leads to my actual question:

What is this thickest head gasket available for the Fiat X1/9-Strada SOHC 1500 engine? (before & after crush specs). Retorque or no-retorque type?

 

[Pete Whitstone]

What is your concern here...

that you will end up with a static CR that is too high for pump gas?

There are far too many variables to accurately estimate what the static CR is going to look like. You are going to have to go through the measurements. If the head is off the short block you intend to use, this is pretty straightforward.

If I had to guess, I would say that you are probably not going to exceed 10:1 with a shave that still has the outline of the cylinder showing. However, you will need to do all the measurements for PV clearance, squish volume, etc., so you can figure out your CR at that time.

Pete

 

[JimD]

Check this old post from Ulix

Hi Jeff,

Not sure if this is helpful or not, but I found this old post from Ulix in the archives:

http://www.network54.com/Forum/12159/message/1142447923/Data

I know this isn't helpful at all regarding your question, but here is a pic of the mating surface on the head I am about to install on the 1500 going into my 78. This is a Midwest-Bayless 10-bolt perf head for FI:

M-B removes pretty much the entire recess around the chamber.

 

[fiatfactory]

Stock type head gaskets (re-torque style) come in 1.2, 1.4, 1.6 and 1.8mm thickness uncompressed, these come down by approx 0.4mm in three retorquing cycles, so end up approx 0.8, 1.0, 1.2 and 1.4 respectively. OEM is Goetze, Tako or Spesso, I've seen all three brands in genuine Fiat packaging, and Fiat make their own as well. Often european packaged Payen gasket kits are Tako or original Fiat items inside

Later style OEM gaskest are "Astadur" non-retorque, these are 1.65mm thick uncompressed and come down to approx 1.5mm, these only come in the type to suit M10 fasteners in 10 and 14 bolt configuration...the head bolt holes are too small to fit an M12 fastener through.

Felpro non retorque is approx 1.65mm thick, and comes down to approx 1.5 /1.55 mm thick.

These are all suit 86/86.4mm bores and "closed deck" blocks (pre 1988) ID of fire ring varies from 87.0 to 87.5.

Later engines for (Tipo etc) have a different gasket again, with a different water jacket hole layout, to suit the "open deck" block of those models.

SteveC

 

[Ulix]

PBS

Hi Jeff,

PBS shaved the head .060" (1.5mm) to make up for the material removed in fitting and deshrouding the larger valves.
With this substantial shave, the CR is back to stock!!

So I would definitely cc the chambers and see what you have, before trying to source an extra thick head gasket.

Also, BVHs work well with hotter cams, and hotter cams only work with increased CR.

 

[Jeff Stich]

that you will end up with a static CR that is too high for pump gas?

I'm mainly concerned about piston<->valve clearance, especially if I need to skim this head once more before using it. Also, I'd rather not have such a high CR that I'll always have to run Premium (97) gas - this is my daily driver/commuter car, & the gas $$ adds up!

There are far too many variables to accurately estimate what the static CR is going to look like. You are going to have to go through the measurements. If the head is off the short block you intend to use, this is pretty straightforward.

The head is off of the block already. I haven't done any specific calcs yet, as I still have to buy new o/s pistons. What I plan on measuring is an undecked stock 1500 shortblock with oversized (86.6mm) pistons (flycut for the larger valves as needed) + PBS BVH 1500 head combustion chambers + thickness of replacement head gasket. Just wanted to know various currently-available head gasket specs to be able to plug in the numbers when doing CR measurements/calcs later. :geek:

 

[Jeff Stich]

http://www.network54.com/Forum/12159/message/1142447923/DataI know this isn't helpful at all regarding your question, but here is a pic of the mating surface on the head I am about to install on the 1500 going into my 78. This is a Midwest-Bayless 10-bolt perf head for FI:

Actually, that photo is helpful - thanks! For a heavily-skimmed head, there looks to be a lot of "meat" still left between the spark plug hole & the head surface. What is the Fiat ID/part number cast into the flat boss on the end of this head (by spark plug #1)?

M-B removes pretty much the entire recess around the chamber.

Was this a Fiat head or a Yugo head? (looks more like Yugo to me) :confuse2:

 

[Jeff Stich]

Thanks, Steve, for all the various brand/measurement specs. This info will help a lot towards me not buying the wrong gasket(s) when it comes time to do so. :thumbsup:

Do the non-Astadur gaskets come in 2 different styles for the 2 different head bolt sizes (M10 vs. M12)? I believe M12 is what my 1300 & 1500 blocks/heads use (will have to double-check that tomorrow). These are all 10-bolt heads & blocks that I have (1980 & earlier).

 

[JimD]

numbas

Hi Jeff,

This is a 1500 10-bolt FI head according to the MWB web site.

The numbers are as follows:

138AE.2A.0085
4430881

 

[Jeff Stich]

PBS shaved the head .060" (1.5mm) to make up for the material removed in fitting and deshrouding the larger valves.
With this substantial shave, the CR is back to stock!!

Now this I did not know - thanks!

So I would definitely cc the chambers and see what you have, before trying to source an extra thick head gasket. Also, BVHs work well with hotter cams, and hotter cams only work with increased CR.

I will for sure be cc-ing the chambers & piston flycuts (once I get the pistons). I'm holding off buying head gaskets until I know all the other CR specs of what I have. Having that info + the various gasket specs will enable me to then buy the appropriate gasket for my set-up. I wasn't sure what the "ballpark" CR was for most folks using the BVH on a non-race street-driven car - 9.5:1-10:1?

The BVH I have came with a PBS S-2 cam & adjustable cam pulley already installed. I've never run this type of cam, so I'm not entirely sure what to expect from it. :huh:

I mistakenly threw out the old head gasket when I disassembled the head/block - d'oh! :doh: Would've likely saved me a bit of guesswork, LOL.

 

[Jeff Stich]

Thanks. I completely missed the "FI" part in your previous post, but yep, there it is. :mallet:

 

[fiatfactory]

Yes, regular retorque type gaskets from most manufacturers come in both M10 and M12 hole sizes... obviously you can use the M12 style for both types... if you look up the Payen numbers you'll find most refer to pre 1980 or 1981 and post these dates... for the change in head bolt hole size.

I have a few of the manufacturers part numbers too if they are any use to you, but I'm away at work for the next week or so and not on my computer...

For pistons you want to find out what CH the pistons being supplied are, and what flycut type too...

128 rally / early 1300 X19 type pistons are 34.7CH with small flycuts at around 2.7mm deep and a tiny 0.6mm pimple dome... regular 1500 USA pistons are around 34.45CH with big flycuts around 7mm deep and flat top... obviously the static CR between the two types is considerable, as well as the squish/quench clearance... some later type 1300 sohc pistons are 34.9mm CH and flat top with the small 2.7mm deep flycuts too... and I've found others (that I use for the 1600 stroker engines) with a 34.15CH which are flat top that come in both small and large flycut variants..so shop around and ask what your favorite vendors have available.

SteveC

 

[Jeff Stich]

For pistons you want to find out what CH the pistons being supplied are, and what flycut type too...

The pistons I'm thinking of buying are OE-type Borgo 86.6mm with flat top & big flycuts, like this:

Supposedly they are OE Fiat part #5881019 (seller also gives several supercession numbers). I do not know the CH on these pistons yet (waiting for reply email from seller).