Re: [stag] Inlet manifold fitment

Hi Leon

Never, never remove material from the flange faces (or even the bolt-holes for
that matter), they are weak enough as it is. Actually, the flanges DO tend to
distort if the fixing bolts are over-tightened, the cardboard compresses and
that is why they re prone to distort even when new. Hacking material off will
only make matters worse.

Look for the root cause of the problem elsewhere, and not to merely mitigate
the consequences as your suggestion is likely to only be a very temporary
repair.

Please follow the instructions to measure the gaps as previously described and
they should be around 0.050", also checking the underside of the manifold is
not fouling on the engine. If you still have the old gaskets from this
engine, what is their thickness? It is just conceivably possible gaskets had
been made up from a thinner material by DPO or he had fitted TR7/slant 4
gaskets which are much thinner.

The correct Payen gaskets are about 0.050" thick, I would think the gaskets
you have are much thicker than that. If the (correct thickness) gaskets are
thoroughly greased both sides before fitment and the manifold gently pressured
downwards, there should be no problem fitting them - a mallet is bound to lead
to fretting problems!

In the final analysis, much better to remove one or even both heads and do it
per Triumph's recommendation. Otherwise I can see leaking manifold gaskets
developing again, possibly with engine damage next time?

IMHO - Mike Wattam
Chairman - Triumph Stag Register
The Only Truly International Stag Club for Stag Owners
Up to date technical advice without vested interests
www.tristagreg.org
Mike@tristagreg.org
Phone: +44 (0) 1202 761051

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-----Original Message-----
From: leonh <EmailWitheld>
To: stag <stag@digest.net>
Sent: Sun, May 6, 2012 4:43 pm
Subject: Re: RE: [stag] Inlet manifold fitment


-----------------------------------------------------------------------------
---
Tjhanks for reposting that Mike. Maybe I am dumb but the proposed solution
does
ot appear to solve my problem...........
y problem is that there are no gaskets THIN enough to permit the holes to line
p.
ruined the Payen gaskets by trying to exert downward pressure on the
manifold.
was trying to settle the manifold into place using a rubber mallet but the
isalignment between the gaskets and the bolts was such that the gaskets broke
t the top bolt holes.
ence the Payen gaskets are too thick.
nother option I was considering was to do BOTH of the following:
Skim no more than 20 thou off the manifold faces.
lot the bolt holes as required. This would then require some time-consuming
ettling of the ports to correct any misalignment.
From an engineering point of view, it is preferable to remove a small amount
of
aterial from the flanges than to exert a lot of pressure on the manifold as
ome have done. This is because the closer the manifold is to the correct
shape,
he less stress will be exerted. In fact it is theoretically possible to exert
o bending stress on the flanges if the mating faces line up perfectly.

-------------------------------------------------------------
ent from TriumphStag.NET [www.triumphstag.net]

Thanks Mike.
It is going to be a while till I can take the measurements as I am travelling heaps for work but when I have done that I will report back and ask your opinion.
I cannot imagine removing the heads so i will be avoiding that if at all possible!
The manifold flange thickness may very well be a weakness in bending, but if the manifold is a perfect fit to the heads then the flange thickness is only required to survive the bolt compression stresses as there will be no bowing or bending. But I accept that this is quite theoretical, and it is highly unlikely to have such a good fit between the manifold and the heads.
Again I find it troubling that this manifold was removed from this engine, and no other displacement has occurred. The compression that must have been put into the manifold is IMO far more dangerous than removing a few thou off the flanges. BUT I am not in a hurry to get this wrong and end up with a blown-up engine. I take your opinion very seriously.

BTW I removed the manifold in order to remove the water pump. I am fitting an electric water pump, and thought that the manifold refit would be a 30 minute job. Goes to show what happens when you play around with things you dont have experience with.

leonh Wrote:
-------------------------------------------------------
> but if the manifold is a
> perfect fit to the heads then the flange thickness
> is only required to survive the bolt compression
> stresses as there will be no bowing or bending.

I disagree, even in theory. The gasket must be compressed, which means the manifold is exerting force against it all the time. Since this is true even away from the bolt holes, there is a bending force applied to the manifold flanges.

Also, the cylinder block expands at a differerent rate due to heat than the heads and manifold do. So there is some force from that.

Sorry I can't help with the original question. My intake manifold went back on easily without removing the heads.

-- Randall
56 TR3 TS13571L daily driver
71 Stag LE1473L awaiting engine rebuild
71 Stag LE2013LBW awaiting (manual + J type) gearbox rebuild

Thanks Randall, I had not thought of the differential thermal stresses between the iron block and ally heads/manifold. It will all become clearer when I can measure the gaps with no gaskets.