1850 exhaust manifold blowing

[Maidstonerob]

A new blow has developed at the manifold to head joint nearest the down pipe. Found the upper bolts loose across the manifold. Is it possible to access the lower manifold fixings without removing the engine? Im sure the starter motor will have to be removed to gain access to the rear lower bolt.

Is there enough room to dismount the manifold in situ if I decide to renew the gaskets instead of a simple tightening?

[xvivalve]

I 'think' on the 1850 you can access the bolts, you can even on the Sprint, but need to jack up the engine on that side after removing the mount.

Question is why has this happened; do you have the gearbox exhaust mount fitted that supports the back end of the downpipe?

[Jon Tilson]

If it has gaskets already and it is blowing I am afraid its 99% that you will need to remove the manifold and change them.
Fear not....it takes me about an hour and a half to do this job....

The trick is 2 fold...trick one is to loosen the n/s engine mounting completely. Trick 2 is to replace as many bolts
as you feel inclined with studs and nuts. The stud will wind in as as far as it can off load and just a nip to tighten it. This will save the threads in the alloy head.

I use a flexi head stubby 3/8 drive socket wrench to get at the least accessible ones. They get worse the further back and underneath you go. It comes with practice....

The studs have the added benefit of supporting the gaskets while you fit the manifold.

If your manifold is straight and flat I would recommend not using gaskets at all...This was how they were made.

May be worth a quick trip to a local machine shop to check it. Once its off it will likely relax and be a bit out, but a quick pass on a machine will have it back flat again.

Use new nuts and a single plain and spring washer under each when refitting and use 20lb ft and no more to save the alloy head.

Jonners

[Maidstonerob]

Glad to hear its do-able.

Alun The mount is fitted to the gearbox. I had fixed a blow at the flange of the downpipe only last week! The two upper end bolts on the mainfold were little more than finger tight, surprised it wasnt blowing already! Havent ivestigated the lower fixings yet.

Jonners thanks for the how to run down. Its a good idea changing the bolts to studs whays the thread size needed for studs are they unf?

[xvivalve]

UNC into aluminium generally

[Jon Tilson]

UNC on the bit into the head and unf for the nuts is what I used. Also a plain shank for the manifold depth. Moss do them.
Common upgrade for TR7's too, but with a different centre gasket for a dolly.

Jonners

[xvivalve]

I'd use UNC both ends and brass nuts, so you can undo them again!

[Maidstonerob]

I'd use UNC both ends and brass nuts, so you can undo them again!

Top tip thanks!

[Maidstonerob]

UNC on the bit into the head and unf for the nuts is what I used. Also a plain shank for the manifold depth. Moss do them.
Common upgrade for TR7's too, but with a different centre gasket for a dolly.

Jonners

Thanks Jonners!

[Jon Tilson]

Rarely disagree with Alun but I will here.

Not sure brass nuts are up to the clamping load you need here. On studs the steel nuts with plain and spring washers always come off for me...

By all means use brass nuts on downpipe flange...but even here I go steel now.

Ive had too many brass nuts strip their thread internally and not come off in my time....

Jonners

[Maidstonerob]

Fitted nos exhaust manifold with heat bandage wrap. Blow now rectified. Having a nice internally clean manifold has slightly but noticeably improved performance.

[Karlos]

I believe that Using an insulating bandage/wrap on the manifold is a great idea. I tried it on a previously owned 1850HL and it made a great difference to the under bonnet temperature as well as actually making the engine feel it had a bit more poke. I am surprised it is not a more common practice as it is a non permanent mod and easily removed for the purists.
I recommend everyone should do it, its a fit and forget mod, worth every penny.

[soe8m]

When soaked in oil it does burn. Some manifolds cannot have such a wrap. For power you need a as cool manifold as possible. Gasses cooling off do shrink in volume and help leaving the engine this way. Hot exhaust gasses staying hot in the manifold and downpipe will cause less power.

Jeroen.

[Karlos]

I read that hotter gases moved faster hence aiding quicker extraction. http://www.performance1coatings.com/cer ... ating-cars
Their intro seems to contradict itself, suggesting cooler manifold temperatures are preferred but higher temperature gas is better.

[Maidstonerob]

I read that hotter gases moved faster hence aiding quicker extraction. http://www.performance1coatings.com/cer ... ating-cars
Their intro seems to contradict itself, suggesting cooler manifold temperatures are preferred but higher temperature gas is better.

Thats what I read that hotter gases move faster allowing better evacuation of exhaust to allow a fuller fresh charge. While adding the benefit of lower under bonnet temperature, they are used on branch manifolds for this reason.