XJ750RL mods/build

sounds like an exhaust leak?

 

Just went to check that and appears one of the screwshas threaded the head... the tapping does sound like it is internal however until I retap this exhaust thread, won't be certain.

 

So, I've now taken the exhaust off. I knew there was some damage to the exhaust 1 of the head but now that I've got a clear view, there's a crack in the thread area of where one of the exhaust screws go. The thread that was in there was half out so I've taken it out.

Queations:
1. How f***ed am I?
2. Is the thread that I've removed, replaceable or is it a matter of re tapping?
3. The crack in the head, opinions on how to fix. Should I rethread, put a bolt in and then weld it?

 

that's a Helicoil you took out, i suggest you put another back in. and keep your fingers crossed

 

That's a helicoil that you pulled out. Ideally the crack should be welded, but it's not too deep so you might be OK cleaning it good and filling it with epoxy.
You can fit a new insert, or if you elect to have the crack welded the shop can fill the hole and tap it like brand new.

 

Ans you noticed, you have an exhaust leak.
The valves sound wonderful, and there's no sign of alernator chain slap that I can hear.

 

I did a little looking and as mentioned above, learnt its a helicoil. I guess my concern of putting a new helicoil of the same size (M6) would be that it doesn't sit tight due to the now slightly wider spot because of the crack, thus pulling out again.

Given that it looks like the hole depth goes deeper than where the original helicoil sat, I'll go a new M6 helicoil in the deep section and use a longer bolt. Along with some epoxy to strengthen the crack.

Once again, thanks guys.

 

the crack was there first i think. then the PO tried the coil to fix it. you'll need a drill bit the right size and the special tap to install it. look up internal thread repair, some people say helicoil isn't the best
it's the only kind i've used

 

Oh, so the helicoil isn't a stock thing? Thanks for that.

 

Helicoil is the only brand of threaded insert used in aircraft (that I am aware of anyway). They've literally been holding airplanes together since the 1930's, and in that application are put into brand new parts prior to assembly (aluminum threads wear poorly, with engine teardowns being an annual event).

 

As a Helicoil has already failed.. maybe it was badly installed. I'd be using a Time-sert similar but one piece not a wire coil. They cost more, but who is counting $ at this point.
http://www.timesert.com.au/index.html

And wont epoxy get cooked / weakened in a head ??

 

You weren't kidding about the price! I do like it though. I'll try a helicoil with loctite and see how it goes. I was thinking about heat and the epoxy, I'll check what chemiwelds can do and if need be, small aluminium weld will have to be done.

 

It failed because of the crack (the bore of the hole widened). Even JB Weld is good for a constant 550 ºF, which is quite a bit hotter than the head gets at the exhaust.

 

Been there, done that with Helicoils. I've used these inserts by Acme Industrial without fail. They use standard sized taps for the threads to set the insert, don't require a install tool, they are solid not a coiled piece of wire and once they are set in place the raised part of the insert are hammered down which locks the insert in place for good. Fastenal can get them for you but they don't carry them as a stocked item. They are the shizzle regarding inserts.

 

I've used similar products to repair spark plug holes in ford engines that spit spark plugs out. Always the full sleeve type like posted above. Haven't had one come back yet...knock on wood

 

We use helicoils on the aircraft for numerous applications . As to JB weld it is great product you just have to make sure it is oil and grease free and mixed properly and left to set up usually 24 hours is ideal. Heat douse not cause problems I have fixed engine cases on VW's with great success .

 

Just to clarify, I wasn't trashing the use of Helicoils. When installed correctly, in the correct application they are a bitchin product.