Hi All,
So my replacement engine is out of the donor car and cleaned. I snapped one of the exhaust manifold bolts and have had no luck removing it even with a stud extractor, so I'm going to drill it out and helicoil it. My question is what size do I need? I'm pretty sure they are 8mm but what thread pitch?
Thanks as always.... He's almost back together!
Part number for the bolts is ERR4961 which is listed in Microcat as Screw - Flanged head M8 Manifold to head, so whatever the thread pitch is for standard M8 bolts I would assume.
Easy to check. Standard M8 is 1.25 mm pitch, if you don't have a gauge 4 peaks in 5 mm or 8 in 10 mm. 8 mm fine is 1 mm pitch, same as standard M6 so hold an M6 bot up to it as a gauge.
Theoretically there is a coarse 8 mm x 1.5 mm pitch standard but I've yet to find one.
I prefer Wurth Time-Serts to Helicoils for DIY as the expanded in place full bush style lets you use loctite for a better fit and includes proper lead in to the thread on the end collar. Helicoils follow the parent metal expansion in hot areas like cylinder heads. Never figured out whether that is good or bad thing overall. Time-Sert prices are obscene, especially when you include tools, but at least you can be sure they re the genuine article. Economy range Helicoil kits seem to be "helicoil compatible" rather than OE. Which makes one wonder as to quality. Like pretty much everything the devil is in the detail when it comes to making things work really well. Helicoil repair inserts coming out with the bolts seems to have gotten more common recently which may or may not be meaningful. Especially when the full provenance isn't known. Just "It's bust, can you fix it".
If I didn't already have the Time-Sert installation gear I'd probably be buying Keenserts e.g. https://www.ebay.co.uk/itm/Thread-Repair-Keensert-For-M8-Bolt-pack-Of-10-/202418854013?_trksid=p2385738.m4383.l4275.c10 as you only need a standard tap and some creativity for installation. Install tool is handy tho'.
Clive
Thanks all. Been a bit sick over weekend so I'll check into it this week and hopefully this weekend do it.
Hmmmm....
I got my 'M8 * 1.25' thread repair kit from Amazon. I measured the threads and they were pretty much 8 peaks in 10mm so I was fairly happy this would be right.
However it arrives this morning and I measured up a bolt to the tap they supply with the kit and the threads do not 100% line up. Although is that because the tap is bigger to get the repair thread in? Anyway, I thought that's OK I'll try to wind the bolt in to one of the repair coils - and it wont even go in..... so my worry is the kit is wrong. The drill they supply has '8,3 HSS' on it and the tap says 'STI8X1.25 HSS' - surely the tap needs to be bigger than the repair it is supposed to be making? Sorry if I sound dim but now I am confused!
Once again help appreciated!
EDIT: Just found this on another forum: 'for the 4.0L the diameter is 3/8, thread is 16, length I believe is 1.25 inches... '
That's why I checked Microcat as I'm sure some of the bolts on the engine are Imperial sizes. As there's no difference between heads on a 4.0 litre and a 4.6, I can't see the threads being different. However, there's different part numbers for the up to 98 and 99 onwards heads and the threads for the GEMS lifting bracket (which I'm fairly sure are the same thread as the exhaust manifold bolts) are shown as 3/8 UNC compared with M8 for the Thor engine. However, if you are helicoiling the holes, as long as the bolt you put in is the same thread as the helicoil, it isn't going to make any difference. On one engine I worked on the exhaust manifold bolt hole threads were stripped due to the bolts having been cross threaded. I tapped the holes out to M10 and then tapped an M8 thread on a stepped bolt so it became a stud with M10 on one end and M8 on the other. Actually made fitting the manifold easier as a stud held it in place while the bolts were put in.
Are the rocker cover bolts imperial? Been a long time since I dug at all deeply into a P38's RV8 but seem to remember this.
Could make up an M10/M8 stepped stud with a bit of welding and grinding. Always a concern drilling into heads (of any type lol) but got to do it to fit helicoils anyway. I'd go with the stepped stud idea rather than helicoil and have done that on Chrysler 3.3 V6 alloy heads.
I had some long M10 bolts that had a thinner shaft before the bolt head, 
that came from a blown Toyota engine I stripped down.
I cut the head off and tapped an M8 thread onto the plain shaft giving me a stud with M10 at one end that would screw into the re-tapped thread in the head and an M8 thread at the other that I could just use a standard M8 nut on to hold the manifold.
Thanks guys. I bought new stainless Allen Key type bolts of the original size, so need the correct thread. Guess I'll send this kit back and get a 3/8" 16 version.
Another sunny weekend wasted.... Sigh.
Rather then helicoiling a manifold bolt, it might be worth having a look for a machine shop that could remove the bolt via spark eroding. I did that with a cylinder head on an old Discovery I owned, worked a treat and there's no chance of you drilling it slightly off centre or not square.
David.
dhallworth wrote:
Rather then helicoiling a manifold bolt, it might be worth having a look for a machine shop that could remove the bolt via spark eroding. I did that with a cylinder head on an old Discovery I owned, worked a treat and there's no chance of you drilling it slightly off centre or not square.
David.
The head is still on the engine unfortunately... and I really don't want to dismantle this engine at all if I can at all help it. Great idea though for those with the engine in bits - never thought of that at all.
Kit worked a treat - thread is now restored. :-)