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Different Way of Machining Big Bore T4 Heads
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Vanapplebomb
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PostPosted: Sun Jun 20, 2021 9:52 am    Post subject: Different Way of Machining Big Bore T4 Heads Reply with quote

I have been thinking lately about 103mm cylinders, and head sealing issues associated with cutting the head registers out to 115mm.

Looking at the material available to work with on the T4 heads, it is occurring to me that simply opening up the existing 100mm (1.7) or 105mm (1.8/2.0) registers to 115mm is removing the most amount of material from the area you least want to remove it from. All that material you would be removing is what helps spread the clamp loads from the studs over the cylinders, and keeps the head from warping.

So, I started wondering…is there a way that big bore cylinders could be run without removing this critical material?

This is what I came up with.

Instead of opening up the head register to fit the OD of the cylinder, why not use the head register as an extension of the cylinder bore? Then, you would only have to make a 115mm cut just deep enough to locate the cylinder, say 1.5-2mm.

Basically, the piston crown would leave the cylinder (~6mm negative deck) but the top compression ring would still ride within the cylinder

The 1.7 head could easily have the 100mm register opened up to 103, then the shallow 115mm locating cut added.

The 1.8/2.0 heads are already set up for 105 cylinders. All you would need to do with those are add the shallow 115mm locating cut.

If you welded up the stock 105mm registers on 1.8/2.0 heads, and shrunk it down to 103mm, you would actually end up with MORE meat on the bone than a stock cylinder head, even with the shallow 115mm locating cut.

The T4 head is built differently than the T1 head, so I see no reason why we should treat it the same way when we machine for big bore cylinders…

Am I crazy, or does this make sense to anyone else?
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PostPosted: Sun Jun 20, 2021 12:11 pm    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

Vanapplebomb wrote:
I have been thinking lately about 103mm cylinders, and head sealing issues associated with cutting the head registers out to 115mm.

Looking at the material available to work with on the T4 heads, it is occurring to me that simply opening up the existing 100mm (1.7) or 105mm (1.8/2.0) registers to 115mm is removing the most amount of material from the area you least want to remove it from. All that material you would be removing is what helps spread the clamp loads from the studs over the cylinders, and keeps the head from warping.

So, I started wondering…is there a way that big bore cylinders could be run without removing this critical material?

Yes. I've done it for customers. Leave as much material intact, then run the piston higher up in the barrel by trimming.
This is what I came up with.

Instead of opening up the head register to fit the OD of the cylinder, why not use the head register as an extension of the cylinder bore? Then, you would only have to make a 115mm cut just deep enough to locate the cylinder, say 1.5-2mm.

Basically, the piston crown would leave the cylinder (~6mm negative deck) but the top compression ring would still ride within the cylinder

The 1.7 head could easily have the 100mm register opened up to 103, then the shallow 115mm locating cut added.

The 1.8/2.0 heads are already set up for 105 cylinders. All you would need to do with those are add the shallow 115mm locating cut.

If you welded up the stock 105mm registers on 1.8/2.0 heads, and shrunk it down to 103mm, you would actually end up with MORE meat on the bone than a stock cylinder head, even with the shallow 115mm locating cut.

The T4 head is built differently than the T1 head, so I see no reason why we should treat it the same way when we machine for big bore cylinders…

Am I crazy, or does this make sense to anyone else?

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PostPosted: Sun Jun 20, 2021 2:50 pm    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

Vanapplebomb wrote:
I have been thinking lately about 103mm cylinders, and head sealing issues associated with cutting the head registers out to 115mm.

Looking at the material available to work with on the T4 heads, it is occurring to me that simply opening up the existing 100mm (1.7) or 105mm (1.8/2.0) registers to 115mm is removing the most amount of material from the area you least want to remove it from. All that material you would be removing is what helps spread the clamp loads from the studs over the cylinders, and keeps the head from warping.

So, I started wondering…is there a way that big bore cylinders could be run without removing this critical material?

This is what I came up with.

Instead of opening up the head register to fit the OD of the cylinder, why not use the head register as an extension of the cylinder bore? Then, you would only have to make a 115mm cut just deep enough to locate the cylinder, say 1.5-2mm.

Basically, the piston crown would leave the cylinder (~6mm negative deck) but the top compression ring would still ride within the cylinder

The 1.7 head could easily have the 100mm register opened up to 103, then the shallow 115mm locating cut added.

The 1.8/2.0 heads are already set up for 105 cylinders. All you would need to do with those are add the shallow 115mm locating cut.

If you welded up the stock 105mm registers on 1.8/2.0 heads, and shrunk it down to 103mm, you would actually end up with MORE meat on the bone than a stock cylinder head, even with the shallow 115mm locating cut.

The T4 head is built differently than the T1 head, so I see no reason why we should treat it the same way when we machine for big bore cylinders…

Am I crazy, or does this make sense to anyone else?


Not crazy at all , a friend has a turbo Autocraft engine that has that sort of cylinder to head match up . Measuring deck height just took a little more work An issue will be to stay inside the head stud holes but I think that would be achievable with 103's .
I run 103's with a 1mm copper head gasket , head torque 30 ftlbs . it is important to anneal the gasket (forgot once and had a minor leak .)
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Vanapplebomb
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PostPosted: Sun Jun 20, 2021 7:32 pm    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

Glad to hear that I’m not the only one thinking like this. Cool

I have thought about gaskets as well. The flat copper gaskets would sort of defeat the purpose of machining the head like this, because you would need to take a deeper cut to accommodate the gasket thickness.

The one thing I do wonder about are the use of copper or stainless o-rings, or even gas filled o-rings. The groove for these o-rings (or fire rings as some call them) could be machined into the cylinders, leaving the head intact.

Porsche used an interlocking stainless fire ring on their last generation of air cooled engines. Part of it sat in a groove in the cylinder, the other part mates to a groove in the head. I don’t think it helped sealing any, but kept fire from torching the head/cylinder mating surface.
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PostPosted: Sun Jun 20, 2021 7:53 pm    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

Jakob at the facebook page “Get Back on Track”. Has sealing rings . He will give out the machining information when you order them ,for the groove in the top of the cylinder .
I was going to go down that path if the copper gaskets did not seal .
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PostPosted: Mon Jun 21, 2021 8:12 am    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

Thanks! I just looked at his page. Very cool.

I see he has used Deutz cylinders. That’s exactly what I was thinking of using. The Deutz 913 cylinders are 102mm. A used set that has been heat cycled would be perfect to shorten, slightly modify stud hole locations, and bore out to 103.
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PostPosted: Mon Jun 21, 2021 2:36 pm    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

Very Happy Very Happy Very Happy Very Happy



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Vanapplebomb
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PostPosted: Mon Jun 21, 2021 6:49 pm    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

Very nice! It looks like you cut off the fins that form around the pushrod tubes, and faced those sides towards each other on this engine? That fits really nice.

I know the 913 102mm cylinders have a big fat 120mm outer diameter (9mm wall thickness) at the head from the factory. Does this neck down at all farther from the head surface, or is it pretty much 120mm diameter all the way down to the base? Just curious, as the bore spacing is 124.5mm. Even opening these up to 103mm, that is a really meaty cylinder.
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PostPosted: Mon Jun 21, 2021 7:52 pm    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

The cylinder is that thick all the way to the base of the fins then steps down for the register in the block . They make for a pretty robust cylinder, over 8mm wall thickness with a 103mm bore!

One day I'd like to build a boosted engine with 100mm bore Deutz's and a 66mm crank .

Something that is an issue with big type 4’s is when using the longer rods for strokers is the 22mm pin .
The JE 103’s that AA sell are an odd size and 2618 forging that don’t last for a street engine .so re boring the the cylinders and going over size is not straight forward . I’m looking at LS 4.065” in a 4032 forging at the moment with a 1.215 “ pin height . That is .030” more than the JE’s but easy to do with cylinder spacers , the 22mm pin is and issue , custom pistons are out of my price bracket , so will be looking at adaptor bushes /caps , that fit the 23.5mm piston but slide onto the 22mm pin .
That will then give a couple of oversizes for future rebuilds .

The other thing I thought of was hard anodising the pistons .
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PostPosted: Tue Jun 22, 2021 3:36 am    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

Wreck wrote:

The JE 103’s that AA sell are an odd size and 2618 forging that don’t last for a street engine.


Are you sure the AA's are true JE pistons. The 2618 piston has more silicon in it which makes for a harder piston with less expansion, with a piston like this you would run less clearance which i don't think would be good on an aircooled engine.
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PostPosted: Tue Jun 22, 2021 3:40 am    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

Bad bug wrote:
Wreck wrote:

The JE 103’s that AA sell are an odd size and 2618 forging that don’t last for a street engine.


Are you sure the AA's are true JE pistons.


pretty certain , I can't remember for sure but I'm sure they had JE embossed under the crown and came in a JE box ( not that means much )
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PostPosted: Tue Jun 22, 2021 5:13 am    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

Back in the early '70s when I rebuilt my stock 1600, I wanted to raise the compression ratio but there was no one locally that would take on fly cutting my heads. I ended up doing something very similar to what the OP is talking about. Not wanting to screw up the sealing surface but wanting to get rid of the smog step I jury rigged a drill press driven cutter that went inside an old cylinder to cut back the step to match the cylinder bore.

This allowed me to trim back the bottom of the cylinders until the pistons came out slightly at the top. The only fly in the ointment was that I didn't know I needed a minimum of 40 thou clearance to allow for thermal expansion so the engine rattled slightly warmed up. On tear down I saw my error but by then had another engine ready to go in and never went back and rectified it. A 10 thou shim at the bottom would have fixed it as they were barely touching.
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PostPosted: Tue Jun 22, 2021 7:48 am    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

The “step” as you say is pretty much what this would be, just taken to the extreme. Like the aftermarket AMC cylinder heads, but instead of a 1mm step like they have, this would be a 5mm or 6mm step.
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PostPosted: Tue Jun 22, 2021 2:14 pm    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

These Wills Rings were roughly what I had in mind.

Here is a link to their product PDF.

https://www.trelleborg.com/-/media/tss-media-repos...56FFA7A613

Pg 17 has reference for automotive uses. Unfortunately, it looks like a limited range of thicknesses for the o-rings. The narrowest groove I see for that style is 5mm wide, which leaves no meat on the cylinder, unless you machine it into the head.

Technetics is another group that does pressurized o-rings. They may have a wider range of sizes, but I haven’t done much digging on their size offerings.
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PostPosted: Wed Jun 23, 2021 8:11 am    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

the pistons on my type 1 were A pistons the crank was 78.8 scat. the pistons did come out of the cylinder about .030 or.040 as I recall might of been more that was long ago. the engine ususlay dont care. I used aluminum head gaskets on that one either .060 or 080 thick to give me around .035 piston to head clearance. that was long ago never any issues.it was 11:1 cr for about a year then I slightly dished the pistons and brought it down to 10.5 cr.
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PostPosted: Wed Jun 23, 2021 10:32 am    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

I also wonder if a ~5-6mm negative deck would help with cylinder warpage issues, since more combustion takes place in the cylinder head, and less in the cylinder. The T4 heads are very good at shedding heat, so with a well tuned engine, I doubt it would run much higher cylinder head temps. Heat in the cylinders is a big factor with warpage. You could have less uncooled area of the cylinder near the top. With only machining the register 1.5-2mm deep, you can have a cooling fin right near the top of the cylinder. By standard machining practices, you typically have 8-10mm of cylinder barrel without a cooling fin.
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PostPosted: Wed Jun 23, 2021 1:03 pm    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

if AA or Qsc made the biral 94's for the type 4, I would put them on my type 1. as I already have some trick very expensive pistons for that size...4 sets. if I didnt have them I wold use the 96's or bigger witch they do sell. the engine dont care what you use as long as it's right in the end.
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PostPosted: Wed Jun 23, 2021 2:26 pm    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

You would need to machine down the cooling fins on the T4 cylinders to fit a T1. The bore spacing is 124.5mm vs the T1 112mm. If you skimmed 5 or 6mm of cooling fins off the inside, and massaged the head stud holes, you would probably be gold.

Currently, the only Biral T4 cylinders I know of are 98mm bore. There used to be 96mm Biral cylinders, but I haven’t seen them in stock for a long time. I don’t really see any use for the 96 Birals in a T4, as heat issues are not generally an issue with the smaller bores. I could see it being beneficial on a T1 retrofit because you loose that cooling fin area on the inside due to the smaller bore spacing.

96mm T4 cylinders are the same as the stock 93 and 94 cylinders, just bored out. Slightly thinner wall as a result, but still pretty stable. Because they are the same head register as the stock 93 and 94 cylinders, there are no real head sealing issues, even with a good dose of boost.

It’s the big bore cylinders that you have to machine the heads to accept that have the issues…which I suspect is largely a factor of how most heads are machined… Machining them like a big bore T1 takes all the meat out right where it is most needed. Hence, the thoughts in my fist post about an alternative way of machining to preserve this material.
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PostPosted: Thu Jun 24, 2021 1:29 am    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

FWIW as the owner of a 71 x 104 with ex-1700 heads, I think this is a great idea.

Even if not taken to the max as described, any amount more material left on the head can only be a good thing?
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PostPosted: Thu Jun 24, 2021 12:35 pm    Post subject: Re: Different Way of Machining Big Bore T4 Heads Reply with quote

I would imagine so.

I have seen some European big bore T4 engines that had an extra cooling fin welded onto the base of the head, for the sake of thicker material around the cuts. And they know a thing or two about Big bore T4 engines.
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