8 Bolt TR6 flywheel/crank.

[vearlytr6]

Hello, I am upgrading? my TR6 motor and would like to know ways of fixing the attaching of flywheel / crankshaft. Two of four threads in flywheel are damaged (first 1/2") Regards,Michael.

[garagewidow]

Hi,

Check how far the threads go into the crank,can't remember but i'm sure there will be an inch or more of thread,then get the damaged area machined out and fit longer bolts.
I've used longer 12.9 tensile allen bolts without issues,if you get some at 3" or so they will have a shoulder(need to check the industry standard for shoulder lengths) which helps to dowel the flywheel as well as the standard dowel.
just make sure they don't bottom out in the hole,measure the depth and cut the bolts at least 1/4"shorter and fit them with quality thread lock.you don't want those buggers coming loose.

You could get 8 holes done but they might compromise the strength of the crank spigot as it isn't that large.

Edited by garagewidow on Friday 13th December 19:30

[vearlytr6]

Hello Garagewidow, The depth of the hole is 1" and the flywheel is 0.4".I can buy ARP flywheel bolts 230-7306 @1.25" but as the first 0.5" in two holes is damaged (has been cleaned with thread tap and can screw a bolt all the way in but...) Regards,Michael.

[tapkaJohnD]

Very similar thread over on the Sideways Technology site: http://sideways-technologies.co.uk/forums/index.ph...

John

[vearlytr6]

Hello Tapkajohnd, It is,I am it. Regards,Michael.

[vearlytr6]

Sorry ,Will post a couple of pictures (if I can) and keep you updated.Michael.

[vearlytr6]

Hello all, here are a couple of photo's of the problem.Regards,Michael.

[vearlytr6]

[LTP]

Find a local machine shop that has Helicoils then get new bolts. I wouldn't advocate cleaning up the damage and reducing the number of threads engaged. Helicoil is a standard automotive way of saving a threaded hole and using the original sized bolts.

You can get a kit and do it yourself if you're handy.
https://www.youtube.com/watch?v=9rtiFBC0wms

[vearlytr6]

Hello LTP, My son has heli-coil sets but we don't think they would be good enough for a 2.5 L flywheel. The plan is to have 7 holes/threads tapped and 5/8" head, longer ARP bolts (to be made by them) fitted. (plus the dowel). Regards,Michael.

[vearlytr6]

Hello, Will post some photos when I get the crank/flywheel and bolts back (they are the other side of the bush fires which have the highways closed at present). 3.5 million hectares and climbing in NSW. Regards,Michael.

[LTP]

vearlytr6 said:

we don't think they would be good enough for a 2.5 L flywheel.

Done correctly Helicoiled holes are as strong as the originals; as you can then use the original bolts the joint is as good as new, if not better

Excessive bolting torque, corrosion and even wear – these and other reasons can lead to thread damage. HELICOIL® Plus thread inserts were developed in a variety of designs, ensuring quick thread repair. The use of non-wearing HELICOIL® Plus thread inserts not only repairs threads but also increases thread load.
Source - https://www.boellhoff.com/gb-en/products-and-servi...

In most cases the newly threaded bolthole is actually stronger when a Heli-Coil™ Insert is installed!
Source - http://www.newmetalworker.com/Reviews/helicoilsrvu...

[vearlytr6]

Hello LTP, The three extra holes have been drilled in flywheel and crank has been drilled and tapped,and going to use ARP bolts p/n 230-7306 1.25" (set of 6 @ $42.27)as ARP wanted $119.04 EACH to finish off 8 x 1.37" bolts. Will put up some pictures when I get the crank etc. back. Regards,Michael.

[vearlytr6]

Here a photo of crank and flywheel. Michael.

[vearlytr6]

Hello, Tried to upload two photos, but it wouldn't work. Michael.

[silentbrown]

Would you need to rebalance the crankshaft after that?