Inlet manifold

[Mike J]

Chasing leaks I discovered the inlet manifold isn't torqueing down as tight as it should. Is it safe to helicoil the cylinder head and refit. or are the threaded holes open and do I run the risk of filling the block with swarf.

mike

[alan_thomas]

Tricky area Mike. Because the heads are presumably bolted down and their position fixed the inlet manifold will not pull them in to allow good compression of the gasket. The common problem is that folk try to tighten the inlet bolts and strip out the weak threads.
I always helicoil all head threads when I am rebuilding and I helicoiled my recent Stag in situ using 5/16UNC helicoils. Very important to get the drill vertical in both planes and they are blind holes so only drill out the existing thread do not go any deeper.
When you have helicoiled then you need to see if your inlet manifold is a good fit with the gaskets you intend to use. If the heads have been skimmed you will need to skim the surfaces of the inlet manifold as well otherwise the manifold will sit high and it will be impossible to start all the bolts. Some people open up the mounting holes in the manifold to allow for this but the inlet is still too high and can cause poor waterway sealing.
Probably one of the worst jobs to do on a stag, it would have been so much better if the manifold were made in 2 parts with each part bolted to a separate head - Alan

[marshman]

Hi Mike,

It is safe to helicoil the manifold mounting holes. This is a link to a thread I started a few years ago when I helicoiled mine. I did have the heads off of the car though so it was easy to keep the holes nice and perpendicular (was going to say square but the holes are round) to the surface. The pictures shown the exhaust manifold side but the inlet side is similar.

https://socforum.com/forum/forum/sta...ing-Heads=&hi=

As Alan says the issue could be the spacing between the heads. Whilst you have the manifold off it is worth a trial "dry" fit to make sure it sits nicely before you fit gaskets etc. You may find you can fettle the fit, especially if some of the flanges have distorted.

Roger

[Mike J]

Many thanks Alan and Roger.

What gasket should I use? Should I use a silicon sealant around the water way?

Mike

[Mark Serj]

Use the Payen type gaskets with Welseal is my recommendation Mike. Silicon can potentially lead to problems blocking stuff up. I used old gaskets on one head fully bolted up, then gauged the gap on the other side to check it was at the same thickness as a compressed gasket, or as close as acceptable to my engineering mind. You can decide from here whether to fettle or machine.

[Robmsharp]

If you do use silicon selant make sure its applied to just around the waterways as applying to the complete surface will cause you a world of pain should you need to remove the manifold in the future.

[marshman]

As Mark has said use Payen gaskets - they are good quality and not "chinese cardboard" and they also have the correct drainage slits in them. Also do as Mark says and do a trial fit using either old gaskets or cut some rough ones from cardboard of a similar thickness to gauge the fit of the manifold.

My approach to gasket sealant is a bit different and is probably more tolerant of any discrepancies in the fit. I use a polyurethane sealant such as Tiger Seal. I smear a thin bead around the openings on the head and then apply the gaskets. I clamp them in place with a large metal bock and leave over night (bear in mind it is easy when the heads are off the car - not so easy when they are still on the car.) This then gives you both heads with the gaskets firmly attached and not likely to slip. I then trim any excess sealant - if you get the bead size right there will be very little to trim. I then fit one head and lightly "nip" up the head bolts and head nuts. I then very loosely fit the other head. Finally I run a thin bead of tigre seal on the flanges of the inlet manifold and ease it carefully into position trying not to smear the sealant. Once seated I fit the manifold nuts, I "nip" up the ones on the "fixed" head first, then I nip up the ones on the loose head and finally "nip" up the head nuts and bolts on the other head. I then properly torque both heads down and then fully tighten the manifold. In my opinion Tiger Seal or any other P U sealant is good in this application because it is strong/tough but still slightly flexible to allow for any slight movement. It also has some "gap filling" properties. I have done several like this and never had an issue with leaks, the down side is it is a pig to clean off if you ever have to remove it!

Roger

[Mike J]

Roger this is excellent. Thank you so much. Tiger seal it is. Reseating the cam covers as well so will use that on there as well. Got another issue with the cam sprocket alignment. Will make a new posting for this. Thanks again.

Mike

[marshman]

Roger this is excellent. Thank you so much. Tiger seal it is. Reseating the cam covers as well so will use that on there as well. Got another issue with the cam sprocket alignment. Will make a new posting for this. Thanks again.

Mike

Mike,

Just be really careful when fitting the manifold that you are sparing with the sealant so you don't have the excess squeezing out on the inside of the ports or waterways.

Regarding the camcovers, I used Tiger Seal to bond the cork gasket to the cover. First check the "flange" on the cover is straight and flat with no kinks, bends, dents etc. (Check it on a flat surface). Once satisfied trial fit the gasket. If you are happy then make sure the surface is clean and grease/oil free and apply a small bead of sealant. Then fit the gasket. I then place the cover on a flat surface and place a weight on top and leave overnight for the sealant to set. Obviously don't use Tiger seal on the gasket to head face, as you want to be able to easily remove the covers. I usually assemble mine dry. Also make sure the rubber half moons at either end of the head sit with the top surface nice and flush. When I replaced mine they sat proud so I carefully trimmed them with a sharp Stanley blade (other brands are available!). I stuck the half moons in with Tiger Seal as well. Not had a leak from either camcover since. Oh and don't overtighten the cover screws - that's how the flange on the cover gets distorted.

Roger

[Mike J]

Thanks again. Where do I get Payen gaskets from?

[dasadrew]

http://lmgtfy.com/?q=payen+stag+inlet+manifold+gaskets

James Paddock, LD Parts, Tony Hart ....... but not Uncle Tom Cobbly

Drew

[jbuckl]

Use polyurethane sealer sparingly as stated. E.G. Tiger seal or MHP etc