Inlet Vacuum Problem

[William2]

I have a problem with the vacuum junction at the inlet manifold. My newly rebuilt engine has been fitted with a hex screw in the inlet manifold hole. I have tried unscrewing this with an imperial size allen key but it refuses to move. Unfortunately the hex screw has now become slightly damaged in this process.
I would greatly appreciate any advice on methods for removing it. Is it best to try and gently drill it out and to hope I don't damage the threads?
Also, can anyone tell me what the thread size is? Many thanks for any suggestions.

[Grizzly]

Could you not Weld a Nut onto it?

[billwill]

Drill a small hole through its centre and then use a stud extractor to get it out.


You might need to heat the inlet manifold.

[CBUEB1771]

You need a stud extractor as Bill says. Careful heating of the casting in the immediate vicinity of the plug will also help. The port is 1/8 inch tapered pipe.

[RichardHawkins]

William,

As Russ says 1/8 tapered pipe. Russ is in the USA and you are in Britain. Russ is probably referring to NPT, whilst in Britain we usually use BSP. These two thread systems and sizes are not the same, but one can sometimes be screwed into the other. This might be why you can't undo the thing. My inlet vacuum connection is 1/8NPT so I assume all are, but with Lotus and the work of previous owners, you can't be sure. From your photograph the plug looks to be steel. Some local heat might loosen it, as aluminium will expand more than steel.

Richard Hawkins

[CBUEB1771]

Actually I was thinking of tapered British Standard Pipe but I should have been more specific. In the nominal 1/8 inch size the NPT and BSPT are close (27 TPI, 0.405" OD and 28 TPI, 0.38" OD) and in my ignorant and impatient youth I have put 1/8 NPT fittings into ports tapped for BSPT. Allen headed plugs in this size can be an absolute bugger to extract. The oil way drillings in the Coventry Climax FWE of my Elite have many of these plugs and they have taken hours and much heat to extract without damaging the tapped holes. Of course they had been in place for 50 years...

[512BB]

Will,

Those stud extractors have never worked for me and I would not use them on any head of mine. Whilst you tighten them into the stud or plug, they can split it and then crack your head. And then you will have a Manekin moment........or similar. Me, my tourets would come to the fore.

If it were my head, I would have to consider if I was going to attempt to do the job in situ, or remove the head. If in situ, you need to stuff lots of clean rag down past the plug, tight, to stop any swarf falling into the combustion chamber. Then drill progresively larger holes, starting with 3mm. Make sure your drills are sharp. As you get close to the diameter of the plug, you should be able to collapse the plug with a small punch or drift, or to just chase it out.

I have used this method many times on the oil gallery blanking plugs in blocks. Works every time, with care.

Good luck with it.

Leslie

[AHM]

1/8 BSPT (at least the ones I have just checked are)

Those stud extractors have never worked for me

Me either - Just makes it worse

[twincamman]

I think I would seal it up with bars leak or liquid aluminium ?.what advantage is there to removal ????or epoxy a fitting around the offending bit ?.ed

[Elanconvert]

1/8 BSPT (at least the ones I have just checked are)

Those stud extractors have never worked for me

Me either - Just makes it worse

x3....first lot I tried broke in the hole...had to buy a special drill to remove it....
second [more expensive ] lot simply turned in the hole removing metal....got a refund though!

agree that drilling + collapsing probably best....and a bit of heat works wonders...

fred

[Elanconvert]

1/8 BSPT (at least the ones I have just checked are)

Those stud extractors have never worked for me

Me either - Just makes it worse

x3....first lot I tried broke in the hole...had to buy a special drill to remove it....
second [more expensive ] lot simply turned in the hole removing metal....got a refund though!

agree that drilling + collapsing probably best....and a bit of heat works wonders...

fred

[rgh0]

I work on a stage strategy to remove stuck plugs or studs / bolts

1. Heat on the surrounding metal and chill spray on the plug or bolt BEFORE I strip it or break it.
2. If that does not work and I do strip it or break it then drill and try an extractor with more heat and chill spray. Taking care not to break the extractor
3. If that does not work then keep drilling it out until the shell can be collapsed

Step 1 works 80% of the time, step 2 gets the majority of the remainder, step 3 is very rarely required. In the end it always comes out one way or another

cheers
Rohan

[William2]

Gents, thanks for all he advice. I will try heat first and if that doesn't work I will go for the drilling option. Fingers crossed. I was thinking of applying the heat using a heat gun on the high setting.

[worzel]

Hi

If the situation gets really desperate (but before you drill a hole right thru for a stud extractor you might consider using dilute nitric acid- this will burn out the steel stud but won't affect the aluminium. You'd need to make some sort of "scoop" to hold the acid pool in place against the head (unless you take off the head obviously).

John

[Chancer]

Being very carefull and precise, I find that a selection of left hand drill bits works for me every time, a centre drill for the pilot hole (the most important step) then enlarge with normal drill bits and finally use a left hand one of just Under the core diameter of the thread. Usually it will back out looking like a helicoil.