Thicker head gasket?

[NixVegaGT]

OK so I've got all the parts back for the engine assembly. With the 5.7" rods and the Ford 255 pistons I've got the piston heads sticking 35 thou above deck. With the 50 thou composite gasket that only gives me 15 thou for quench. DAMN! I thought I was done.

Now what? Somehow find a thicker gasket? Mill out the head chambers by 15 thou where the quench is?

[NixVegaGT]

I figured it was about time to cc the heads. They came out to 45cc!!??! I checked a few chambers to double check I'd gotten it right and it was the same for all of them. I cc'd the piston heads too. That came out to 2cc. So I was tossing around the idea of running premium (92) gasoline a couple days ago but that will never work now. I guess it's official I'm going with E85 for certain now.

I got a little mill for my dremel and I'm planning on recessing the heads where they quench by 15ish thou for a bit extra clearance for the pistons. That leaves me with about 30 thou quench.

SO after all those measurements, including the extra couple cc's in the quench clearance, I'm at 13:1 static compression. The cam I got from Woody closes the intake valve at 71º ABDC, that combined with 1.68 rod ratio gives me a dynamic compression of 9.8:1. Not too radical for E85.

So has anybody heard of 300 heads with a cc that small? Maybe it's the valve heads?? I just don't see them making up 9 cc's though.

[Moderator]

"So has anybody heard of 300 heads with a cc that small?"

My first thought was that these must be 35 year old heads and maybe in all the years before you got them, they might have had a previous valve job. If so, I imagine they might have been skimmed. (This might possibly have been done if they were slightly warped, or if the gasket surface got gouged, or...) I just did a super quick calculation. It looks to me like removing 6 thousandths off a 3.5" cavity would reduce volume by about 9.5cc - and that would drop overall volume from about 53cc to about 43.5cc.

[BlownMGB-V8]

I suspect Curtis is right. There are several options open to you. First option, machine the piston tops to bring them down closer to what you were looking for. A lathe will do this quite well and quickly too. With a .050 gasket you'd only have to take off .025" to get a .040" quench and that's a very light facing cut. Measure carefully and don't forget to allow for piston rock, as your piston crown height can vary by several thou. This is the option I would recommend as it is easy and won't affect anything else. The pistons should easily tolerate removal of that much material, and if you want to adjust your compression downward at the same time it is a simple matter to cut the dish deeper also while retaining the quench area. I would not go any thinner than .040" on the quench, .040-.050" is effective and smacking the head is not a good option.

If you don't want to do that, thicker head gaskets would be the next option. I don't remember what you did for head gaskets, but going to .080" here would accomplish much the same thing, though you might find you need to add a gasket to the intake manifold. All in all a bit messier but certainly feasible. But if you know a friend with a lathe the choice would be obvious I'd think.

Jim

[NixVegaGT]

Thanks for the input. After I backed off and relaxed for a couple hours I reevaluated my situation and I'm feeling much better. With the DCR at 9.8:1 I'm actually in better shape for E85 than I was before. It does make me really happy I got that cam from Woody. The DCR with the Crower 50232 was at about 11.4:1! Unexpected. What's strange is the intake with the Crower cam is only 1º BTDC (@ 0.050). huh... The Erson is at 17º (@ 0.050). I guess it's different theories about what's optimal.

Good point about turning the top of the piston but I'd have to disassemble the whole bottom end and it's all spec'd out and lubed up. Alternately I started milling the quench on the heads. It's working pretty well. Here's a pic of what I've done so far. It's pretty easy. Just takes a steady hand and a bunch of arrogance.

You cannot view this attachment.

I can't wait to find out the valves hit the top of the piston. LOL.

[BlownMGB-V8]

Well now THAT's an interesting approach. You know what I'd do? Get a steel shim head gasket to check, rub prussian blue around the tops of the pistons, bolt the head on and spin 'er around then check  for blue marks. Once everything clears your .050 gaskets will give you the .040 quench. Or just use a few .010 shims for checking.  I've heard minimums of .090 and .120" for the valves, what're you shooting for? I'm still waiting on head gaskets for mine. Pan clearance has reared it's ugly head, on both engines. Buick didn't allow any extra space there. The 340 will get double gaskets.

Jim

[MGBV8]

I'm with Jim. I would shave the piston tops. Seriously.

[NixVegaGT]

My dremel has an adjustable fence for depth. I've been setting it with shims as a guide then I double check the depth with a depth mic. It's been pretty close to ± .002 ish.

I will totally check with the blue. Good idea, Jim. What do you use? Dyechem or something. (Did I spell that right?)

I've still got to get my lifters and push rods ordered to check the valve clearance but mathematically the valve is open .050 @ 17º BTDC. The valve is already 120 thou away from the piston when it's closed. LOL! SO I've got some more grinding to do... DAMN!

[NixVegaGT]

OK I worked out the valve reliefs in the piston. Here's a pic:

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I'm not excited about having to do this. I'm confident I'm just not looking forward to the hours of work. Does this compromise the piston strength at all? They will be about 100 thou deep. On the upshot, I didn't realize these heads have such a shallow valve angle. I could see it before but I've never really thought about it. I worked it out to around 8.5º. Does this sound right? WOW that's flat. No wonder they perform so well.

I figure these reliefs will increase volume by about 2cc. That reduces my static CR to about 12.5:1 and DCR to about 9.2:1.

[BlownMGB-V8]

And you still aren't going to pull the pistons? Well, I guess it'd be possible to mask off everything.... but seriously, do you really want to cut all those reliefs with a dremel? That's not going to do anything for your balancing job.

There's a saying I always remember when I find myself in a situation like this. "Anything worth doing is worth doing twice." That means, when I find the need to tear down and reassemble something that is already done, it was already expected and is not a surprise. That lowers the barrier of internal resistance to the point where, usually within a day I can overcome it. I try not to make irrevocable decisions during that period.

Working on pistons ought to be characterized as a series of precision machining operations, once the forging operation is over. It is not artwork, not even of the finest sort, and artwork really has no place there. Combustion chambers and ports are a different matter entirely. You could argue that there should be some leeway with the domes, especially if you are prepared to match the piston weights precisely afterwards, but in my opinion it should be avoided. Flathead engines with pop-ups are an exception in regards to the transfer scallops to some degree as well, but even that is mostly done by machine. Since you have already begun cutting the chambers there's no going back and you may as well finish it. Prussian Blue is a non-drying high pigment paste often used to check contact patterns such as with dies and gears. any similar pigment could be used but Dykem is not it. Dykem dries and will not transfer. As for the cutouts themselves, there is no substitute for direct measurement, and a little blue on the edge of the valve will mark the spot. Use a (very) light spring on the valve for checking. Rotate the valve while in contact with the piston to mark it. The exhaust side often will not need to be cut even if the intake does. Check every 2 crankshaft degrees. A .100 deep relief should pose no problem.

Jim

One other thought. If you have a scrap head and an oversized valve it would be possible to grind the valve as a cutter, use a depth stop, and cut the reliefs using a drill on the valve stem with the head bolted to the block. This method will give precise location, depth, and edge clearance but will put chips in the bore. Vaseline or some other method such as tape can be used to minimize that.

[NixVegaGT]

Yeah man. I'm with you on all of it. The hard part for me is trying to figure out a way to hold the piston so I can machine it OR I could take everything apart and have the pistons custom milled. Either way I'm kinda feeling like taking everything apart and starting over.

I really like the idea of using an old head with a valve cutter. Nice. I'm gonna sleep on it a few nights.

[NixVegaGT]

Look what I found:
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Not inexpensive but I guess guys do this all the time. I've also discovered that JE makes something similar. Since I've only got to cut about 100 thou it should work great.

[BlownMGB-V8]

Yep, that ought to do it.

Jim

[NixVegaGT]

So I mentioned I got my parts back. Well since I decided to have the valve reliefs cut into the pistons I had them shave the piston heads 30 thou. That coupled with the valve reliefs and head work I did my Static CR is now 10.83:1. With my cam choice that puts me at about 8:1 DCR. Pretty much optimal for regular old pump gas.

SO out with the E85 and back in with old fashioned gasoline. LOL! Unless I decide to turbo charge it later I suppose. That probably will not happen though.

Interesting developments. Thanks Crew!

[BlownMGB-V8]

Sounds like you're pretty well set. Ought to be a fine running mill when you get 'er done.

Jim

[hoffbug]

Nik..
 Why not  build everything E-85 compatible now.. Then even if you dont switch at some point you will have a super corrosion resistant system.. and if you do switch youll be all ready.

[NixVegaGT]

Yes. I have already set the whole fuel system for E85 so I'm golden. Good point, Tony.

[TRip]

Hi Nicholas,

Before you go through all the work of calculating, CCing and grinding, may I suggest that you have a look at Cometic head gaskets.

The company makes custom steel (less compressability issues when torqued down) gaskets with custom thicknesses.  Used on race and other performance vehicles.

I haven't used them and only recently started researching them as part of my future TR7 V8 build.  Reviews seem to be quite good, though.  Do a search for them on the net.

They also appearantly work very well to address other Rover/Buick issues such as coolant weeping and cooling system pressurizing via gasket.

Maybe this will help you get an easy solution to your clearance issues. Perhaps worth a look.  Hope it helps.

http://www.cometic.com/custom.aspx

http://www.cometic.com/catalogs/AutoDomestic.pdf

Cheers

Trip

[TRip]

From the Cometic site:

"Can I order a head gasket with a different thickness than you have in your catalog?
Yes. Call Cometic with the engine type or Cometic standard part number (search online or in our catalog) along with the thickness you would prefer and we will create your custom gasket. (800-752-9850 or 440-354-0777)"

Trip

[roverman]

Nic, so you've had the pistons "topped" and valve reliefs re-cut at 10 deg.? You've also "dremeled" the  the squish/quench areas of head? If I "had" to cut these areas, I'd use a verticle mill or farm-it-out. Use head gasket as a template, located by the (2) dowels, a flycutter set to correct diameter and angle of cut, finese/tram into position using gasket or digital X-Y coordinates. If you've already balanced your engine, the reworked pistons will give you, "overbalanced" condition.Maybe not as silky smooth at lower rpm., but less "I"-loads at higher rpm. Have you "peeped" at Performance E85 webbsite? Lots of sound data available there. Some people are running "Boochu" compression with it. Personally, I dont see much point of having squish and quench with .050" min., but that's just me. Good Luck, roverman.

[NixVegaGT]

Hey man. The valve reliefs are cut at something like 7.5º if I remember right. Our heads have a really shallow valve angle. COOL. I used the head gaskets as a template and cut the heads the old fashioned way then cc'd the volume. The difference was minimal at ≈ 1cc.

The machine shop told me that I shouldn't notice a big difference in balance because the amount of material removed was small compared to overall weight and equal amounts were removed from each piston.

On the quench: You mean you don't think it will matter on our engine? or that .050" isn't enough?

I assembled the engine for the last time yesterday. I couldn't torque the rods because I didn't have the stretch gauge handy. That will have to come later. I was able to check the actual final dimensions of everything. I initially thought the pistons were going to be shorter at .012 above deck but when everything was assembled for the last time I ended up with .035 above deck. Right where it was when I started:

Head Cc: 46
Piston Cc: 4

Deck: +.035
Quench: ≈ .038

Head gasket dia: 3.77"

Bore/stroke: 3.74 x 3.4
Intake valve ABDC: 68º (@.050 + 15º) (adv: 71º)

CR: 12.6:1
DCR: 9.54:1 @ 1000 ft. (9.72:1 @ sea level)

Not huge compression but I'm happy with it. The pistons are not forged so it's just as well I'm not pushing it there. Since detonation is so ulikely with E85 I could get away with lighter/weaker pistons. We'll see how it turns out. It could be they don't last and I'll start this process all over again. LOL!

So no more waffling. This is where the numbers are. My course is finally set.

[roverman]

Nic, since your pistons are not "race" I'm thinkin you have pin offset? Know how much? This will reduce "I" loads at turn-around and lateral thrust.  I'm sure you ring-gapped for Hyper,(hotter)piston per mfg'r? Your pistons should have minimum rock at reversal. Some of the reasons for squish and quench areas are to reduce end-gasses from going-off prematurely, (detonation), also to provide beneficial turbulence. The more one increases gap clearances the less effective they become. Personally, I prefer less than.05", aluminum rods not withstanding and considering rpm/stretch. I hope all of your effort is returned in "the loud pedal", roverman.

[NixVegaGT]

Boy me too. I fought with the engine all morning with a game I like to call the Heli-coil suffle! SUPER frustrating. I'll start a new thread for that. I'm sure we'll all chime in. LOL.

Pin-offset. Is that were the pin centerline is above the shear surfaces? I think so... Never checked this though. I did gap the rings VERY carefully. It took a few long hours. I gapped them to each respective cylinder and kept them with the pistons the cylinders where blueprinted to. Hopefully that will pay off a little.

[hoffbug]

Damn.. If I wasnt sick Id invite myself over for a look.. :-)

[MGBV8]

Nick,  Art is talking wrist pin offset.