Targa Tasmania - checking the damage

[Colin Byrne]

So have started having a look at the damage incurred during the latest outing, and once again i'm back looking at broken headers and engine mounts....

So while it was the vulcanised rubber of the engine mount that failed at Targa high Country, this time it was the metal part that attaches to the engine block.  Not surprising you might say, except i'd already gone over this part and made some strengthening mods, but some more required me thinks!

So i've decided to through away pretty much the entire mount, which mostly comprises of folded metal parts spot welded togeather and look at getting some real strength using some relativly thick wall tube. 

As you can see from the photo the down side to this is its fairlyl heavily fabricated so i'll be sending it away with the repaired headers to get profesionally stress releived before i install it in the vehicle

I've cut of the cracked primary flange and tube off and replaced it with a new part, also added some strengthening braces from the flange back to the next larger diameter tube in an effort to reduce the clear stress concentrator at the flange,

so here we go again.....

(we've started talking about looking at the root cause of the issue and looking into some sort of vibration damper on the engine, but its a complicated issue so much more investigation required, stay tuned)

[LaStregaNera]

How are your extractors joined to the rest of the exhaust? Bolted flange? Slip joint? Sprung joint?

[Colin Byrne]

good question!

Yea spent a fir bit of time on this end of things, and have a really good slip joint arrangment, the rest of the exhuast is very well supported and i'm confident there is no extra stress being generated from the rest of the exhaust, i've also redesigned the gearbox mount for the end of the extractors, still rubber mounted to allow for heat expansion ect, but tried to support it a bit better

[bonno]

Hi Colin
Do you think a flexible joint close closer to the front end of exhaust might fix the cracking of headers similar to the one depicted on photo. Maybe the rigidity of the exhaust could also be causing the broken engine mounts.

[Colin Byrne]

Yea those joints work well, i did run one for a while, the down side to them in my opinion is whilst they allow good flexability in bending and for/aft movement, they don't allow much compliance in rotation, which i think is pretty critical due to the amount of rocking the engine experiences.  Apparently the ribbed inner core is also not ideal for exhaust flow, but that could also be BS.  the old man has had good results with the flex tube pictured below, it allows for some torque compliance and you can get some good quality clamps to suit, however you need a reasonable length of it to work and the clamps are fairly bulky and with my side exhaust setup i just don't have the room, however i'm confident my slip joint arrangement allows for even more moment than both those type of joints

[105gta]

Hi Colin. ford escorts have a similar design of engine mount but the world rally cars changed the design to use a cylindrical bush with a through bolt to Overcome most of these issues.
Might be worth looking into if rules allow it.
Search mk2 ford escort World Cup mounts you'll get the idea.
I believe they started with using the front eye bushes from the rear leaf springs but now days you can buy all kinds of different hardness bushes for the application.
Ben

[Colin Byrne]

Great tip! Just had a look and really like the concept definitely negates the issue of the vulcanised rubber part catastrophically failing could probably use the 105 rear trailing arm bush too, definitely worth considering thanks

[bazzbazz]

Ok, as for the broken headers, may I suggest that you need to weld bracing laterally between/across the pipes along the length of pipe where the fracturing is occurring. This will allow them to brace together rather than each pipe on its own.

As seen on a 159 manifold below you see the webbing between the piping, in your case you would simply weld thin lightweight flanges between the pipes.



You get the idea.

[LaStregaNera]

good question!

Yea spent a fir bit of time on this end of things, and have a really good slip joint arrangment, the rest of the exhuast is very well supported and i'm confident there is no extra stress being generated from the rest of the exhaust, i've also redesigned the gearbox mount for the end of the extractors, still rubber mounted to allow for heat expansion ect, but tried to support it a bit better

I can't help thinking a sprung joint like JK's book describes, and Spruell recommends might sort a big chunk of the issue. 

[Colin Byrne]

Good suggestions, i did try the spring joint method a while ago, once again that method doesn't allow much movement in the axial rotation direction, as i mentioned my slip joint is very well aligned, it's almost a completely non contact joint, i'm confident there is very little force being transmitted between the two parts

as for the 159 manifold idea, the issues i have is with cracks running around the tube at the flange due to the large stress concentration created between the heavy flange and the much thinner wall tube.  I don't think the webbing concept will add any extra strength in that area, and i'd be a little concerned with tieing the tubes together that close to the head given the huge amount of thermal expansion and contraction the primary's go through, it could actually cause extra stress on the flange joint rather than reduce it

Took the extractors down to the heat treatment place on Monday so should have them back soon