10mm to 8mm head studs

[Bashr52]

I've got a solid late model case with 10mm head studs that I'll be boring out for 94's. Should I convert to 8mm to avoid the cylinder holes getting to close to the threads on the 10mm studs?

[Dan Ruddock]

Yes you should, there are even more reasons to than what you have stated. Dan

[modok]

Probably yes, but
I'd love to hear the story of how the engine case made nearly 50 years without needing case savers. Must have involved a very long period of inactivity.

[jpaull]

I was contemplating the same as you little over a year ago. I usually built all the engines with 10mm studs and figured I would try the 8's. After building/running/maintaining a 2+ liter with the 8mm's i can say that I regret using the 8's and wish i never chose them. Even the nice military spec chromo 8's feel like they are twisting if you go anything over 18ft lbs. I have heard the "expansion is matches engine more with 8mm" theory. But the 10mm stud engines have always been bullet proof. I also dont like 94mm thinwall cylinders, and have since went back to 92 thickwalls and back to making more power, which is against most samba users rationale.

Others have mentioned if you use 10x12 case savers there is no worry of boring into them.

[evanfrucht]

I had a head stud strip the threads in my OG case and now I'm building a new motor....

So yes, put in case savers.

8mm, or 10mm. CASE SAVER Inserts

8mm are strong and will make your life easier

No reason to stick with 10mm studs, unless you simply already have them and want to use them.

Always use original german studs too, the new chinesesium "chromoly" ones are junk
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[Dan Ruddock]

The 8’s decrease the chance of a cracked case.

[RWK]

Type 4 use's a 7.2 mm stud with 12mm threads in case, for comparison.
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[jpaull]

[Matheus]

[oprn]

In the 2 dozen or so engines that Dad and I rebuilt in the 70s we only found one stripped out 10mm stud hole and back then there were no case savers. These were all stock engines and stock rebuilds so perhaps high HP engines do need them but stockers don't?

I suspect abuse in either the building process or in the use of these failed stud engines. Or perhaps there is a HP limit to the stock set up? It seems the newer cases from VW had them so is it related to the high temps required for emissions?

Screwing the bloody things in and out every time you have the engine apart is not going to help either.

[Ohio Tom]

If you plan on anything north of 150hp, you had better give 10mm studs another look..

I know that many will argue with me on this.
Even folks in EU say they can put 400hp thru 8mm studs....
I see heads lift at 200hp with 8mm stock studs.

Even Raceware 8mm have their limits.


Ask any real drag racer, and they will always say 10mm hands down.

Just like what was said above, 8mm studs are "stretchy".

If stretchy is OK with you, then go for it..

[oprn]

The other thing that could be causing a need for case savers is Loctite. Use of that stuff in aluminum just about guarantees the threads will come out with the studs! A bit of oil on the threads or anti seize like Copper Kote goes a long way to insuring the studs will not gall the threads in the case and the threads will be ok next rebuild.

[vwinnovator]

Back in the day I recall reading a service bulletin for rebuilding 10mm stud cases.
The practice was to torque the 10mm to 50ft/lbs. If the stud didn't pull the case would not need inserts.

I've seen quite a few 10mm cases with pulled studs (cause of loose heads) through my years.

Inserts are cheap insurance wether you go with 10mm or 8mm studs.

When vw introduced inserts on later cases, '73 on(8mm stud), you have to also remember they came out on dual port engines which had a little more power.

perhaps they did so because the first dual ports, '72, has 10mm studs without inserts which were prone to pulling...."B" cases seem to have been notorious for this

Anyone else remember the self tapping 10/12mm studs to replace a pulled stud without tearing down the engine?

[Dan Ruddock]

Too much head heat pulls the 10mm stud without out savers and 10mm studs with savers in time will crack the case if run with high head temps. Very rare to see a 40hp with pulled studs, they ran cooler than the latter engines. Detonation will also crack cases with savers and 10mm studs. I only use og 8mm studs. Never a problem even on a 160 hp engine. I have built up a large stash of used ones over the years. I have seen the same problem on old VW diesel engines where the the head bolts pull the block apart right at the end of the bolt threads, the same place the crack starts on the air cooled VW engine, right at the very end of the case saver. Dan

[Matheus]

[vwracerdave]

Everybody has their theory. VW went back to 8mm studs with inserts because they expand at the correct rate. 10mm studs without inserts were pulling out of the case because they didn't expand when the engine warmed up. If your under 200 HP there is no reason to use 10mm studs. If you have a 10mm case I would have it inserted and use 8mm studs for anything larger then a stock engine.
_________________
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1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[Matheus]

[jpaull]

Dan Ruddock wrote:

10mm studs with savers in time will crack the case if run with high head temps.

So racers running 10mm studs and no fan belt abusing their engines with super high head temps 1/4 mile after 1/4 mile should be cracking their cases right?

I have drove my 10mm case saver engine to the track on 95 degree day without all its engine tin, unsealed engine compartment, with no seal and huge gaps everywhere, no sled tin or venturi ring, and running "cool tins" which is the ultimate samba no-no. Then took the belt off, made passes all day, put the belt back on, and drove home. Why no case cracks for me?

I looked through all the Cracked case samba posts and I cant find anyone having a case saver area crack like you mentioned. They are all un related cracks like oil temp senders and other areas.

[Bashr52]

Specs are 82x94, 10.5:1 compression with an FK10 on ported 050 heads. I have no issues staying with 10mm, just concerned about material getting thin around the larger cylinder hole and the case threads.

The case is an AK code, so I was surprised to find that is was a deep stud 10mm. I thought all the late model cases went with 8mm studs with inserts.

[Lingwendil]

I'm pretty sure that the changeover was in the first couple months (February, I think?) of the 73 calendar year. The AE block that came in my 73 super is 10mm stud with deep number three.
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