3.2SS top end rebuild - compulsory newbie questions

[Jeff Alton]

Originally Posted by Nux

Yes I agree. The final torque value will be unknown - just like Bruce said. Apparently both methods work? But how about re-torque after break in?

With a digital torque wrench (to accurately measure degrees of rotation) final torque WILL be known as it is displayed. Re torque is not mentioned in the spec book because it is not required.

Cheers

[Nux]

Originally Posted by Jeff Alton

Re torque is not mentioned in the spec book because it is not required.

Cheers

Perfect - thank you.

[KTL]

The new nuts are just coated with something different. Old were gray, probably uncoated, and the newer version were simply yellow zinc chromate (yellow passivated)?

[Nux]

Additional question:

All piston rings are good. Cylinders too with good cross pattern.

Should I replace rings anyway?

[Trackrash]

Originally Posted by Nux

Perfect - thank you.

I think part of the confusion is between "re-torque", "re-tighten", or check tightness?

FWIW, After 150 miles on my new motor, I put a torque wrench on my head nuts and they all needed about a quarter of a turn to get them up to spec torque. BTW, I used VR base gaskets.

I had to pull the top end apart, don't ask, and when I reassembled I used OE base gaskets. This time after 500 miles I checked the torque on my head nuts and they are all still tight.

YMMV.

[onboost]

Originally Posted by Nux

I'm currently doing a top end rebuild of my 1978 SC based 3.2SS. This started out as a classic Max Moritz kit on otherwise stock engine. Since my purchase I've added EFI/ITB, 1 5/8 Headers and CDI+ignition (classic retrofit).


Oh and last: I'm installing DC20 cams. There seems to be some conflicting timing numbers on these. I keep reading 2.2-2.4, but Joh Dougherty states 1.8-2.0?!?! Anyone with experience?

Thanks!!!

What size EFI/ITB were you running and with what cams previously?

[Nux]

Originally Posted by onboost

What size EFI/ITB were you running and with what cams previously?

43mm ITB's , 30LB injectors. Before was standard SC cams.

[onboost]

Originally Posted by Nux

43mm ITB's , 30LB injectors. Before was standard SC cams.

What kind of ITB? Are you bumping-up your injectors, and what led you to move to DC 20 as opposed to something a little more aggressive? Oh, what CR?

Always curious as to what drives particular choices, pro/cons.. other limitations etc..

Thx

[Nux]

Originally Posted by onboost

What kind of ITB? Are you bumping-up your injectors, and what led you to move to DC 20 as opposed to something a little more aggressive? Oh, what CR?

Always curious as to what drives particular choices, pro/cons.. other limitations etc..

Thx

It's the kit from Closed Course Motorsport (Clay's) which uses Triumph 43mm throttle bodies and Clay's manifolds. The 30LB injectors should be good for 280hp or so. Don't think my build will go beyond that (I wish....)

I initially went for 993SS cams, but since I'm not building a race car and since I got the DC20's dirt cheap, I though I would give it a go. Should be a "hot 964" cam.

I haven't measured the CR yet, but it should be 9.3:1 or 9.8:1 (Mahle made two different kits). I did consider gong for JE's or similar with 10.1:1 or even 10.5:1 - still single plug. Slippery slope. And again, very unsure about the high-comp-single-plug combi. I know guys who're running very high comp on their 2.7's - but not really anyone with larger displacements. So spend my money on some Wevo stuff and fresh paint instead.

So in total: Hopefully a street friendly 230isch rwhp (naive I know....) 1950lb hot rod Targa when it's all done.

[Neil Harvey]

You cam measure the angle (somewhat) with a simple torque wrench. From where you start the turn to when the wrench click's.

But the angle method is a lot more accurate. It removes all friction, wrench errors etc. 90° is 90°.

Biggest problem with these heads is making sure the heads don't collapse under the head nut washers.

[faapgar]

Hi,on your setup with the weepy head seal I have found that the factory 3.2 head gasket repair kit works the best.I think the part # is 930-104-381-01 This works very well if your head surface has been machined.Use valve grinding compound & lap the cylinders to the head.Place in the oven & warm to 200 degrees.Wear a pair of gloves & wipe the surfaces with ATF on a rag as the pores are all expanded.The repair gasket is made of Inconel with a silicone like coating.Finish cleaning with Brakecleen.It will never sweat oil again.I use these gaskets on Turbo motors as well with great results.Good luck with your build.Oh,these are not expensive.Ciao Fred

[safe]

My 3.2 had leaky heads (and one broken studs at the end).

I can't remember if I had the heads machined, I don't think so... Maybe I lapped them with grinding paste.

Then I bolted it up with Supertec head studs, no leaks 6-7 years and 30.000 miles later.

I used the same studs on my 3.6 rebuild too (that had leaks even though it had the updated seals), no leaks yet, but its only 2 years and few miles.

If I build another engine I'll use the same studs. No re-torque, set and forget.

[cgarr]

Those gaskets are .020 thick work great to repair heads that have been cut to far too, to keep things stock height you will need to machine your heads .020 from the stock height of 84.5mm




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[KTL]

Fred & Craig make a very good point about those gaskets being beneficial if your heads have been machined. Because if you plug the added thickness of these into a compression ratio calculator, they have a considerable impact on the difference.

For instance let's say for the sake of simplicity and calculating, you have a dead on 98mm bore, 70.4mm stroke, typical 90cc combustion chamber volume (should actually be a bit less if the head is machined, but let's just use the original unmolested volume) and a measured piston dome volume. Dome volume is dependent on the piston type/shape and it obviously dictates compression ratio. Let's use a value of 33.5cc because it produces a typical Euro SC compression ratio of 9.3:1 when you calculate everything out.

Also in the compression ratio calculation is deck height. Let's say your cylinder base shim/gasket is sized good. Meaning, the original base gaskets that were used when the engine was first built at the factory are 0.25mm and let's say you increased them to 0.5mm to hit your desired 1mm of deck. Now by adding that 0.20" (0.5mm) head gasket because you'd like it to seal as best as possible, you're effectively going to be raising your cylinder height and that means you're now going to have 1.5 mm deck. That additional 0.5mm of deck height reduces the static compression ratio.

Here's the calculation

Bore (mm) 98
Stroke (mm) 70.4
#cyls 6

Bore radius 4.9 (cm)
Stroke 7.04 (cm)
Resulting displacement (cc) 3186.15 This is Pi x radius x radius x stroke x 6 cyl.
Single cyl. displacement (cc) 531.02 This is the above displacement divided by 6
Deck Height (cm) 0.1
V1 Swept V (cc) = single cyl. displacement = 531.02
V2 Deck V (cc)= 7.54 = Pi x radius x radius x deck height (0.1cm = 1mm)
V3 Head V (cc) = 90
V4 Piston Dome V (cc) = 33.5

Compression ratio = (V1+V2+V3-V4)/(V2+V3-V4) = 9.29:1

Now change the deck height to 0.15 in the above calculations and your resulting compression ratio is 8.83:1, which is a difference of 0.46.

So my point is you have to recognize using the gasket has a significant effect on deck height and compression ratio. Ideally what you should do is "cheat" a bit and use the minimum thickness cylinder base gasket (0.25mm) when you are using these cylinder head gaskets. Which is more important to you, deck height, cylinder sealing or compression ratio? 1mm of deck height is a general rule of thumb to make sure you have ample clearance from the edge of the piston to the edge of the combustion chamber. But there's nothing in the original engine specs that says 1mm is the absolute minimum to be adhered to. Folks who build race engines often go quite a bit below the 1mm.

[Neil Harvey]

Maybe also consider the volume that is around the fire band down to the top ring and the diameter of the fire band. This makes a difference to your numbers if used.

Often on these older pistons the fire band is upwards of 6.0mm tall and the piston OD there can be 1.0mm smaller.

[Neil Harvey]

Street engines with stock parts would make the compression ratio the most important. You do not have the luxury to establish a deck height as well as a compression ratio without one effecting the other.

Race engines should be as tight as possible with the piston "cleaning" the carbon off the chamber every time it reaches TDC.

[Nux]

My deck hight is currently 0.7mm with 0.25mm base gasket. I have no records of the heads or cylinders being machined. I believe it's the standard Mahle "max moritz" kit.

Using the above calculations, I have a CR of 9.6. However, I have previously read elsewere that the Mahle big bore pistons for the 3.0 engine (3.2ss) were 28.4cc and the 3.4ss piston was 33.5cc.

In that case, the CR is 8.94. I'll have to measure my piston domes.

Does the base gasket seal anything? I've seen posts from engine builders who claim they never use a base gasket?

[Trackrash]

.7mm deck height sounds like you are cutting it close. But yes you can assemble without the base gaskets. My old motor does not have them and it never caused problems or leaks.

Let us know how the CCing comes out.

[Alan L]

The base gasket is to seal against crankcase pressure - nothing like the cylinder head pressure. If others can get away without them, you probably can - just make sure totally clean before seating. Else may get oil weep from crankcase. But dropping the gasket out will make your deck height worse (smaller)?
Alan

[Nux]

Originally Posted by Alan L

The base gasket is to seal against crankcase pressure - nothing like the cylinder head pressure. If others can get away without them, you probably can - just make sure totally clean before seating. Else may get oil weep from crankcase. But dropping the gasket out will make your deck height worse (smaller)?
Alan

Yes my deck hight would be about 0.5mm. I need to verify my deck hight and measure the piston domes. Would like to have a CR close to 9.8:1