Thread inserts in the Norton head

Joined
Feb 7, 2010
Messages
3,876
Country flag
I, like many others, assumed the helicoil would be first to let go, rather than last. Guess I'll keep that box of spark plug helicoils.
 

Time Warp

.......back to the 70's.
VIP MEMBER
Joined
Dec 3, 2012
Messages
1,996
Country flag
Wow.... and thanks for the kind offer the other day Jim.

Does that mean there is only around a 3 to 5 ft/lb margin on those studs based on the test if they are meant to be torqued to 30 ft/lbs.
Inch pounds is sounding like a much safer bet and torqued for sure.
 

Deets55

VIP MEMBER
Joined
Oct 3, 2013
Messages
1,202
Country flag
Here I have tested 4 common inserts used in the Norton head. These inserts were all 1/2 inch long. They all fit a 3/8-16 stud.


Jim,

I’m curious to know what a standard non-repaired hole will release at. I was very surprised how little wiggle room there was in the torque range. Do you think the waisted bolts add some flexibility because of their ability to stretch a little.
Pete
 
Joined
May 7, 2005
Messages
4,056
Country flag
And if these only have a 3 to 5 ft/lb margin then the smaller original finer threaded holes must be under 30 ft/lbs, no wonder they fail.
 

Time Warp

.......back to the 70's.
VIP MEMBER
Joined
Dec 3, 2012
Messages
1,996
Country flag
And if these only have a 3 to 5 ft/lb margin then the smaller original finer threaded holes must be under 30 ft/lbs, no wonder they fail.
What if...

If the 3/8-16 helicoil went to 35 ft/lbs @ 0.500" , how much at 0.625" ?

If you surmised that at 4.375 ft/lbs per 1/16" , at 0.625" that might add another 8.75 ft/lbs or fail at 43.75 ft/lbs which would be a much safer margin.
 

jaydee75

VIP MEMBER
Joined
Jul 2, 2012
Messages
708
Country flag
Thanks, a great test. What does a non-inserted stud pull at?
Jaydee
 

acadian

VIP MEMBER
Joined
Mar 5, 2010
Messages
941
Country flag
This is fantastic, thanks Jim. I'm getting ready to repair some pulled cylinder head studs on an A65 (the through studs going into the barrel), so this is timely information.

Do you think there would be any difference in cycling between the different inserts? Would the results be different in, say, a cast iron barrel as opposed to an alloy cylinder head?
 

comnoz

VIP MEMBER
Joined
Dec 10, 2008
Messages
7,193
Country flag
This is fantastic, thanks Jim. I'm getting ready to repair some pulled cylinder head studs on an A65 (the through studs going into the barrel), so this is timely information.

Do you think there would be any difference in cycling between the different inserts? Would the results be different in, say, a cast iron barrel as opposed to an alloy cylinder head?
In a ferrous metal the solid insert would be the strongest.

In aluminum pieces that are exposed to heat, the flexibility and coarse thread on the od makes the regular helicoil the winner.

The main reason the Bigsert fails is the fine thread pitch on the OD.

To beat a regular helicoil in aluminum takes a solid insert that is considerably larger and with a very coarse thread.
 
Last edited:

comnoz

VIP MEMBER
Joined
Dec 10, 2008
Messages
7,193
Country flag
Thanks, a great test. What does a non-inserted stud pull at?
Jaydee
I have actually never tested one with the original thread at high temp, except on the bike where it failed when I tried to torque it to spec when it was hot.
 

comnoz

VIP MEMBER
Joined
Dec 10, 2008
Messages
7,193
Country flag
What if...

If the 3/8-16 helicoil went to 35 ft/lbs @ 0.500" , how much at 0.625" ?

If you surmised that at 4.375 ft/lbs per 1/16" , at 0.625" that might add another 8.75 ft/lbs or fail at 43.75 ft/lbs which would be a much safer margin.
The extra length would definitely help as long as there is enough thread on the stud to take advantage of it.
 

comnoz

VIP MEMBER
Joined
Dec 10, 2008
Messages
7,193
Country flag
Prior to this test, the only tests I had done was testing regular helicoils and comparing them to the inserts that I was making from aluminum bronze.

That is where I found I had to go really big and coarse to beat the regular old helicoil.

Thanks to the engine builder down the street for loaning me the timesert taps, I was able to do this test.
 

comnoz

VIP MEMBER
Joined
Dec 10, 2008
Messages
7,193
Country flag
I, like many others, assumed the helicoil would be first to let go, rather than last. Guess I'll keep that box of spark plug helicoils.
Regular helicoil inserts -not the solid ones- work fine for spark plugs. Just install them 2 or 3 threads deep to keep them from coming out.
And then remember to go a step colder on the plug because they don't transfer heat as well.
 

comnoz

VIP MEMBER
Joined
Dec 10, 2008
Messages
7,193
Country flag
Jim,

I’m curious to know what a standard non-repaired hole will release at. I was very surprised how little wiggle room there was in the torque range. Do you think the waisted bolts add some flexibility because of their ability to stretch a little.
Pete
The only time I have used a waisted stud for these holes is when I was using an aluminum barrel.

Since the cast iron barrel that the stud passes through does not expand very much, the waisted stud doesn't help.
 

comnoz

VIP MEMBER
Joined
Dec 10, 2008
Messages
7,193
Country flag
The strongest insert I have tried in aluminum was a regular 1/2-13 helicoil with an Ez-lock insert inside of it.
 
Last edited:
Joined
Aug 30, 2006
Messages
354
Country flag
I made M14 x 2 mm bronze inserts:



Combined with longer studs.
You can make longer studs using a head bolt, than you already have the correct cycle tread.


about head bolts ( off topic..): with a spacer on the centre bolt you can use 5 bolts of the same length, wich IMO is better than 4 long and 1 short.
 
Last edited:

lcrken

VIP MEMBER
Joined
Mar 15, 2009
Messages
3,962
Country flag
Another fascinating surprise, Jim. Thanks for posting. Definitely not what most of us would have expected. I've been using the Timeserts routinely for years on cases, cylinders, and heads on the assumption that they were stronger than helical inserts. Oh well, at least I haven't had any of them fail (yet:rolleyes:). And in some cases, there just isn't enough room for the larger diameter inserts (like with cases bored out for 920 liners). In any case, it looks like the best option is a larger OD insert, if possible, and very coarse OD threads whatever the insert size.

Ken
 

comnoz

VIP MEMBER
Joined
Dec 10, 2008
Messages
7,193
Country flag
I made M14 x 2 mm bronze inserts:



Combined with longer studs.
You can make longer studs using a head bolt, than you already have the correct cycle tread.


about head bolts ( off topic..): with a spacer on the centre bolt you can use 5 bolts of the same length, wich IMO is better than 4 long and 1 short.
14mm-2 inserts is what I have in my head. But I use a 3/8-16 internal thread.
That leaves a little material left in case I should ever pull one to go to the 16mm -2 insert.

And yes, I use the long outer bolt in the center of my head along with a deeply finned spacer.
 
Top