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Cam fasteners

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Tgt6 Avatar
Tgt6 Joao Simoes
Ann Arbor, Michigan, USA   USA
1973 Triumph GT6 MkIII "GT6 Cabriolet"
1973 Triumph GT6+ (MkII)
Do folks here reuse these 2 bolts used to attach the cam to the cam sprocket? I ask because it seems to be a unique bolt with a shiny shoulder which I have never seen before. Also I am using a double row sprocket now on my GT6, though I don't think that matters.



A penny for your thoughts but everyone gives their 2 cents' worth...somebody is making a penny.

Joao

197? GT6 Convertible
1965 Volkswagen Karmann Ghia Coupe
1950 Dodge Meadowbrook

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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
I have re-used them, but on occasion I have felt them yield before the required torque.

In those caes I have replaced them with standard grade 8 bolts.
Nothing special as far as I know.

I do use a plate with lock tabs as was OE.

tapkaJohnD Avatar
tapkaJohnD John Davies
Lancaster, Lancashire, UK   GBR
Joao,
A "bolt" always has a 'shank', the unthreaded part below the hex-head. It's stronger than the threaded part, and bears better on a smooth bore. The thread should extend to no more than one turn inside the bore that is fastened.

A bolt that has threads right up to the head is a "machine screw", from its use as an adjustment control.

Once you get into your Spitfire, you will see many examples of the first, in high stress applications. Big end bolts, the bolts that hold the prop shaft flanges together, and similar studs such as the head studs.
Machine screws are used for low stress fasteners, eg sump bolts. You will have seen the timing cover bolts, and noted that some of the fateners for that have slotted heads - none of them need to be done up tight, especially the ones into the alloy bridge piece!

That your cam retainer bolts have shiny shanks makes me wonder if they were loose, and the fastner was fretting on them? Is the shine all around the bolt? If so, then that's the way they are - non-original, which have a black passivated finish - so no problem then. Fretting wear would be on one side.

John



Edited 1 time(s). Last edit at 2017-12-04 02:48 AM by tapkaJohnD.

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clshore Carter Shore
Beverly Hills, Florida, USA   USA
Understand that regular bolt shanks are NOT finished to exact size.
They are sized to fit inside of a standard sized hole.
So a 5/16" (0.3125) bolt will have a shank that is smaller than 5/16".
How much smaller? there is no real standard.
This vendor specifies that they can vary from 0.3125" to 0.3065"

http://www.americanfastener.com/cap-screws/

Also, when torqued to spec, those bolts DO NOT prevent the sprocket from moving around on the cam.
When torqued to 25 ft-lb, each bolt generates about 4000 lb of clamp force.
It is the FRICTION created by the 4 TONS of clamping force that holds them securely in place.

You can find special bolts that do have a shank which is ground and finished to an exact size:

https://www.ebay.com/sch/i.html?_nkw=5%2F16+shoulder+bolt

But none of those are used on our cars, they cost about 10x as much.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
What are peoples thoughts on the locking plate (bent corner tabs) that often seem to go missing after a sprocket change?

tmpass Avatar
tmpass Tim P
Medway, MA, USA   USA
1970 Triumph GT6+ (MkII) "Capo"
1970 Triumph GT6+ (MkII) "Blue Oxide"
In reply to # 1501361 by Tonyfixit What are peoples thoughts on the locking plate (bent corner tabs) that often seem to go missing after a sprocket change?

Loctite should suffice,(what version ??) but they probably shouldn't be re-used after bending and removing... making a new one would be easy enough.

clshore Carter Shore
Beverly Hills, Florida, USA   USA
In reply to # 1501361 by Tonyfixit What are peoples thoughts on the locking plate (bent corner tabs) that often seem to go missing after a sprocket change?

Usually there is enough virgin material on the tab to bend up and lock the bolt head.
If not, use a new one, or as Tim says, use Loctite.
Note that in the absence of the tab, it's important to use a flat washer under the bolt heads.
This prevents the bolt head from altering your carefully positioned cam timing when it is tightened down.

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tapkaJohnD Avatar
tapkaJohnD John Davies
Lancaster, Lancashire, UK   GBR
Delete, complete borrocks.

Sorry!
John



Edited 1 time(s). Last edit at 2017-12-04 04:26 PM by tapkaJohnD.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
I have seen washers used in place of the locking plate with a chord of the washer turned up to lock the nut eye rolling smiley

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Wolfcreek Steve Steve P
Central, Wisconsin, USA   USA
Get crazy, use locking wire! Bolts are almost never used a positioning device, (AKA shank fitting tight in a hole) that is what a dowel pin is for.

tmpass Avatar
tmpass Tim P
Medway, MA, USA   USA
1970 Triumph GT6+ (MkII) "Capo"
1970 Triumph GT6+ (MkII) "Blue Oxide"
In reply to # 1501398 by Wolfcreek Steve Get crazy, use locking wire! Bolts are almost never used a positioning device, (AKA shank fitting tight in a hole) that is what a dowel pin is for.

then you nee new tools and bolts too...






Edited 1 time(s). Last edit at 2017-12-05 12:42 PM by tmpass.

clshore Carter Shore
Beverly Hills, Florida, USA   USA
In reply to # 1501398 by Wolfcreek Steve Get crazy, use locking wire! Bolts are almost never used a positioning device, (AKA shank fitting tight in a hole) that is what a dowel pin is for.

First, the Spitfire cam bolts DO NOT NEED safety wire.
Second, safety wire is OBSOLETE.
It's use dates back to at least 1918.
If it were not still MANDATED by FAA regulations on aircraft, NO ONE WOULD USE IT, except folks doing historical aircraft restorations.
It's highly effective when done properly, not so great when done wrong.
BETTER methods have been invented over the past 100 years!

Here's one I just saw at NASA Tech Notes:

http://www.katofastening.com/lockone.html

joppamoto Mark R
Crestwood, Ky, USA   USA
Still mandated in motorcycle racing.

14GPDJENGINEERING Avatar
Silver Spring, MD, USA   USA
Being an ex helicopter mechanic trained by our U.S government, I preferred to use AN bolts with washers, Loctite & safety wire.

https://www.pegasusautoracing.com/advcat.asp?CategoryID=ANBOLT



Dennis smiling smiley

clshore Carter Shore
Beverly Hills, Florida, USA   USA
In reply to # 1501443 by 14GPDJENGINEERING Being an ex helicopter mechanic trained by our U.S government, I preferred to use AN bolts with washers, Loctite & safety wire.

https://www.pegasusautoracing.com/advcat.asp?CategoryID=ANBOLT

Belt, Suspenders, AND buttons winking smiley
Helicopters, particularly, are in a constant state of attempted self-disassembly.

Please note the number of OEM cars and trucks that employ safety wire.
And how often do the critical fasteners come loose?

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