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Author: Subject: Replacing x-flow inlet manifold bolts (& stud)?
David Jenkins

posted on 29/7/18 at 09:37 AM Reply With Quote
Replacing x-flow inlet manifold bolts (& stud)?

Lately I've been faffing around with carb swapping (the bike carbs are back on!) and I've found that the inlet manifold bolts and stud are a real PITA. With the original manifold I couldn't get an ordinary socket properly onto the head of most of them, making the correct tightening with a torque wrench really difficult. It's impossible to get my socket onto the nut that holds the underneath of the manifold at the centre, and my socket doesn't have a particularly thick wall - I have to freestyle/guess that one with an open wrench.

I was wondering whether I could replace all the bolts with good-quality socket cap-head ones, probably with a flat washer underneath. I have a set of 1/2" sq. hex keys that might fit, or I could buy just one imperial-sized key for this job. Can anyone see any problems with this? They're only tightened to 15-19 ft/lb, so super-grade steel bolts aren't required.

I was also wondering if I could replace the central stud with a bolt (I don't know the thread of the bit that goes into the head at this time) to make life easier there too. This assumes that I could remove the stud without breaking it, which is always a significant risk - it would be a case of "try to remove it gently, and give up if it won't yield easily".





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DW100

posted on 29/7/18 at 09:43 AM Reply With Quote
Yes is the simple answer.

It always used to be common practice on crossflow race engines.

If I remember correctly they are 5/16 UNC.

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David Jenkins

posted on 29/7/18 at 10:04 AM Reply With Quote
Thanks!

5/16" UNC sounds about right. Does that go for the stud as well?





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DW100

posted on 29/7/18 at 10:17 AM Reply With Quote
Yep used to replace all of them, inlet and exhaust manifold.
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David Jenkins

posted on 29/7/18 at 10:22 AM Reply With Quote
Not fussed on the exhaust side - they're easy to do.





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David Jenkins

posted on 29/7/18 at 10:27 AM Reply With Quote
quote:
Originally posted by DW100
Yep used to replace all of them, inlet and exhaust manifold.


Being excessively lazy this morning - can you remember what length they are?





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snapper

posted on 29/7/18 at 10:36 AM Reply With Quote
You need a longer socket with a large circular hole so stud goes through





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David Jenkins

posted on 29/7/18 at 10:46 AM Reply With Quote
quote:
Originally posted by snapper
You need a longer socket with a large circular hole so stud goes through


Not as easy as that - the socket fouls the underneath of the original manifold, and the coolant pipe on the bike carb manifold.

[Edited on 29/7/18 by David Jenkins]





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rusty nuts

posted on 29/7/18 at 11:29 AM Reply With Quote
If it's any help David I have a few spare heads that I can take the central stud out of and measure. My manifold is held on with normal bolts apart from the central stud which as you say can be a pain . I will be changing the exhaust studs and nuts for socket head screws next time I have the exhaust off for the same reason. If you have problems getting the replacement S/H screws let me know , there is a place in Linton that's very helpful .
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David Jenkins

posted on 29/7/18 at 11:58 AM Reply With Quote
Thanks Mel

I should be OK - there's a first-class fastener supplier in Ipswich (Suffolk Fasteners) so I hope to be able to get them there. They're also quite low-priced!

quote:
Originally posted by rusty nuts
If it's any help David I have a few spare heads that I can take the central stud out of and measure. My manifold is held on with normal bolts apart from the central stud which as you say can be a pain . I will be changing the exhaust studs and nuts for socket head screws next time I have the exhaust off for the same reason. If you have problems getting the replacement S/H screws let me know , there is a place in Linton that's very helpful .






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David Jenkins

posted on 29/7/18 at 12:50 PM Reply With Quote
quote:
Originally posted by David Jenkins
Being excessively lazy this morning - can you remember what length they are?


Decided not to be lazy - they're 5/16" UNC x 1.25"





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steve m

posted on 29/7/18 at 09:11 PM Reply With Quote
What inlet manifolds are you using, as ive never had an issue, putting nuts and washers on either short or long tract twin 40 manifolds, nor the 28/36dcd manifold on my xflow,

Ive always used studs and nuts, as its easier to mount the manifold on a stud than a bolt, but at the very worst use studs on the furthest apart holes to centralise the manifold, and possibly use bolts on the other three

steve





Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at




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rusty nuts

posted on 29/7/18 at 09:31 PM Reply With Quote
In my case it's a homemade inlet manifold with fairly large ports using Kawasaki ZZR1100 throttle bodies , the exhaust is a bespoke large bore manifold that doesn't have enough room to get a socket or ring spanner on the cEnter two nuts
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posted on 30/7/18 at 08:54 PM Reply With Quote
I have never ever had a problem fitting / removing the manifold nuts. I always use a 3/8" drive socket. I probably have 6 manifolds in the garage and they all work just as good and nothing different in the castings.....
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David Jenkins

posted on 31/7/18 at 09:02 PM Reply With Quote
To be perfectly honest, I can just about cope with the 4 bolts that hold the manifold - it can be a struggle sometimes to get the socket on properly, the extension bar often rubs against the manifold itself, and it can be a pain when doing things within the engine bay (the chassis gets in the way).

It's the centre nut-on-a-stud that's a pain - I can't get at it properly with a socket as the inlet pipe is quite close on my bike carb manifold. Even if I used a long thin-walled socket, it wouldn't get over the chassis problem.

I will convert to socket cap head screws in the near future as access will be a whole lot easier all round. They're on order, and should arrive tomorrow!





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rusty nuts

posted on 31/7/18 at 09:15 PM Reply With Quote
I got mine today 4 for 15
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