Mix of 8mm and 10mm studs iin case , what torque settings

I have a 1600 dp engine with a mix of 8 and 10 mm studs from a previous owner. I am reconditioning the heads and I need to know if I should use one torque setting for all studs or the correct settings 18 ftlbs for the 8 mm and 23 ftlb for the 10 mm.

If anyone has experience with this or understands the problem from a technical perspective I would very much appreciate the help. If I use 23 for them all they may pull out or stretch and if I use 18 for them all they will not be tight? Is this correct?

To me it's a big no no having mixed studs, why don't you replace them all with new 8mm studs

Nooooooooo

How much trouble is it to remove the old 10 mm studs and insert 8 s. Do I have to remove all the cylinders

matberry wrote:Nooooooooo

What do you mean ? More info please

If you use a mix of studs along with there different torque values it will apply different clamping forces to case, just remove the 10mm studs and fit the 8mm studs using case savers ,you will have to spend the money to have this done but then you will start off with a set of the same sized studs. don't do a lash up as it will come back to bight you later.

imo777 wrote:

matberry wrote:Nooooooooo

What do you mean ? More info please

It means you should not mix studs.

Well - you can do what you like, but if you want the motor to last you should pull it down and fix it

Trouble is i dont believe you can install savers with the case together.
You will need to split the case

Thanks for the feedback , does anyone know if case savers can be installed without splitting the case

Fitting case savers requires drilling holes and tapping new threads. Some of the stud holes go through
into the the crankcase, so the swarf from the drill and tap will end up inside the motor.
The question I need to ask is what studs are original, and which studs have been replaced.
I assume the 8mm studs have been replaced by the 10mm.
How many have been replaced?
Dave

About half are 8 and half are 10. I don't know the history of the engine I bought the car with it. The 10s screw into the block and the other have inserts. Is there any way to tell
Imo

So if the case needs to be split to even up all the studs I'm not doing it at the moment, maybe in a year or two. So in the interim what torque setting should the studs be with a mix of 10s and 8s, I'm thinking 18 to 20
Imo

Yes, a bit bogus with different studs,
and likely it was an early case originally with M10 studs.

To get you back on the road, tension them at the spec for the individual stud.
i.e. 18lbs for the M8 and 23lbs for the M10.

Please use a lubricant on the threads, and between the nut and washer.

The two different pitches mean the clamp on the head is similar even though the torque is different.

When it gets up to operating temperature though, it will be anyone's guess!

My racing engines have used extra studs above and below the barrel,
and the torque recommendation are smaller torque for the smaller stud,
but in my case, the smaller studs are "additional", so not totally relevant comparison.

Thanks dangerous
I called a friend who is a mech engineer and he asked me about the pitch on the threads . He also said the tension on the bolt was what mattered but that was impossible to measure in my situation. So the different pitches make a difference it seems.
Thanks for your input- I have used this engine for 7 yrs with the odd studs and it still runs fine so I'll go with your suggestion unless any one else has had direct experience in this situation , and I'm pretty sure the original studs were 10 mm

Thermal expansion isn't dependant on cross sectional area / diameter of studs, thus the 8 mm / 10 mm shouldn't make a different in that respect.

However, elastic expansion is. > area, < deflection. so given pressure pulling the case studs out... 8 mm will provide more 'give' than 10 mm. Thats logic though anyways.

If ur putting up with the mixed studs, i'd say drive to divide the 10 mm / 8 mm evenly so the 'give' of the 8 mm is divided evenly.

Its a 1600... not like its some hypo turbo etc.

my 2c.

Thanks bajachris - there are many variables at play here
Imo777

TBH I'd try to find a loan engine until you can fix your properly just because no matter what any of us say you're running dissimilar parts and hence a bigger engine breakdown could occur because of the dissimilar parts.

However, I would first suggest removing an 8mm stud and clamping it in a bench vice. Then use a large socket to act as the head and tighten the nut to the torque for the 10mm studs. It's not a very high value but testing in a vice will let you know if the stud can handle the slightly larger torque.

If that test works out OK then do them all to the 10mm torque and then you have less chance of barrel to head blowby due to incorrect clamping forces.

Going a lower torque may work but a good chance the 10mm studs will work loose giving you blowby.

Thanks for the reply
Is there any reason not to use a high temp loctite to make sure nothing moves?

Dangerous has given you some good advice...take it.

If you want to waste money, and know you will never need to strip the motor again, then Loctite would be nice. 🙄

Thanks Greg
Sounds good

Sorry but go with Dangerous' advice with the quality lube and not loctite IMO as a more true torque value will be attained, and remember clean, clean, clean, parts and threads/nuts

Sweet thanks Mayberry-there seems to be a consensus from some switched on vw nuts