Cracking Exhaust Manifold

[Mick]

Hey i have attached a photo of what happened to my old exhaust manifold, i noticed the car started to sound louder and louder from the engine bay and when i took the cover off i saw that it had cracked and seperated into 2 pieces, i could stick the tip of my little finger into the gap, anyways i got a secondhand one and put it in and its been fine for years, but lately i have noticed it making the same noise as last time so i think its cracked again, why would an exhaust manifold do this for so often?

why would it even do it at all?

is it something common?

[admS15]

Are you using the correct factory Nissan yokes, washers on the studs. They are intended to allow movement of the manifold as it expands and retracts from heat.

[Missileman]

You also need to tighten then to the correct torque, and because getting a torque wrench in there is almost impossible, most 200lb gorillas tend to over tighten them.

You can get by this problem by setting to correct torque on the wrench and then slipping the open end spanner onto the 1/2" drive of the torque wrench and feeling with you gorilla hands how much you need to tighten them, not exactly precise but it does the trick.

[Trex]

funnily enough i have been reading about na tuning and old small blocks lately. The biggest contributor to cracked exhaust manifolds have been running the engine lean, hot.

 

Is the exhaust properly supported? engine mounts? loose mani bolts? etc

There was another bloke on here about a year ago who had gone through 2-3 standard manifolds also.

[Dobz]

How much track work has the car done? The colour of it suggests it's been copping a lot of heat. 

[tridentt150v]

yep...white=heat

[Mick]

i dont know if it's white cos before i installed it i had it sandblasted and i painted it with a vht exhaust paint that was aluminium colour

[Mick]

the car gets no track time and i dont thrash it, so this is just normal use

[Mick]

and a very good question about the washers, i had a few studs broken so i removed the manifold and removed all the studs and replaced them, they were a little longer but fit well, im pretty sure i used those special concaved washers but i will double check, i do know that after i tightened them all up i did not ever check or retighten them, im not sure if i was supposed to have done that or not??

[admS15]

There is obviously something that is causing this since it keeps repeating itself. It may be time to get a good workshop to take a look and see if they can point anything out. As I have already said,

- make sure all the studs are still there and your using genuine nissan yokes and washers

- make sure all exhaust hangers and braces are intact and the way the exhaust system is mounted isn't putting any stress on the manifold

- check your engine and gearbox mounts are ok and not allowing excess movement that can stress the exhaust and manifold.

- if all that checks out, put the car on a Dyno and have afr's checked to make sure it's not running too lean.

There has to be an explanation somewhere.

[Trex]

I've deleted your other 3 threads asking the same question.

 

I'd suggest re reading my post, and adms15's..

[Mick]

they were different posts like one asking if there are any aftermarket direct fit manifolds and stuff, and yes i told them what happened and put a link to this thread, i didnt think that was against rules, i could have got good help from someone who hadnt read this specific thread in it but you thought it best to delete them, just seems weird seeming these threads are to help people, i really do appreciate your post and it is very helpful for me and others but other peoples posts and thoughts are also helpful and didnt really need to be deleted in my opinion, but i see the need to keep the forum clean but they wernt the same threads reworded. The more replies with helpful hints and thoughts the better.
 

Anyways i think it might have something to do with my timing being out from the belt needing to be changed a lot of kms ago, but yeah i will give everything a good checkout, thanks all dor the help

Edited July 5, 2017 by Mick
wrong info