Lotus Elan and Lotus Elan Plus 2 Forums

The exhaust manifold gasket has blown on no.4 cylinder (fabricated manifold). Can I replace this without removing the whole manifold?
It looks to me as though it should be possible, but what do I know!
Roger.

If the Manifold is attached with Bolts rather than Studs it's a possibility.
You will have to loosen all of the other Bolts in order to achieve a big enough gap to remove the old Gasket & clean the sealing surfaces.
In doing that you will have disturbed the other Gaskets which should also be replaced as they probably won't seal properly after being disturbed.

I did ---- just slide the new gasket in place with cap heads --remove the stud or notch or slit the gasket holes [ if your on the clock ]- it sealed up well ----replaced the studs with cap head bolts ---for future service and ease of header removal during engine removal and installation --also reused the 3 remaining old gaskets with no problems -----not F 1 standards but it still works --ed

Yes I have replaced a single blown gasket on a fabricated manifold on No 4 cylinder. I use socket head cap screws not the orginal studs, so I just remove the screws, pull back the flange a fraction and pull out the gasket, slip in some abrasive paper and clean the faces, slip in a new gasket and bolt it up again.

No need to remove the other 3 cylinders connections. Easier to do on 4 or 1 than 2 or 3 as better access withiut the thermostae house and the pipes are a little more flexible

Incidently I use high temperature silicone sealant ( Loctite Red or copper) on exhaust gaskets at the head to aid sealing. The water cooling in the head keeps the gasket cool enough so that the silicone does not burn off.

cheers
Rohan

Hey Rohan.. All,
Have you done any mods to the head to accept the socket caps? have you helicoiled for eg? or similar?

I was considering doing this also. 1.25 x std torque can be applied and less chance of thread wear etc. A great idea methinks for various reasons..

Alex....

Alex ---just double nut the stud --back it out and install the bolts ---if you want to be racy you can drill and safety wire the cap heads for that 'boy racer look' --I used washers ---ed

Got no problems taking out the studs Ed.Thanks though.. I was just interested to see if anyone had 're-enforced' the threads in the head to take the socket caps. Taking these in and out a lot and constantly tightening/slackening etc will wear out the threads in the head,hence the 'Helicoils or similar' question. Puts steel threads where you want them and you can put more torque on the cap screws. (1.25 x the standard torque)...Handy that..

Ab....

alexblack13 wrote:Got no problems taking out the studs Ed.Thanks though.. I was just interested to see if anyone had 're-enforced' the threads in the head to take the socket caps. Taking these in and out a lot and constantly tightening/slackening etc will wear out the threads in the head,hence the 'Helicoils or similar' question. Puts steel threads where you want them and you can put more torque on the cap screws. (1.25 x the standard torque)...Handy that..

Ab....

It's a well made point Alex.
Maybe for the first time or two it will be OK to screw the Bolts directly into the Aluminium Threads in the Head, but those Threads will give up the more the those Bolts are fitted & removed.
The Engineering solution is to use Studs, as per original, but a 2nd best solution would be to fit Helicoils whenever it is possible to get at them properly.
Longevity is then practically guaranteed.

Hmm, thanks for the advice. My headers are on studs so that could be a problem, I can't really tell if there is enough clearance to pull the pipe away from the head far enough to disengage it from the studs. Would it ruin the integrity of the gasket if I cut two slots in it so I could slide it into place?

nick the gasket where the mounting holes are --- header pressure holds things fine --and its not like you aere removing the bolts many times -----ed

I have to say that I bought some cap screws with the thought of using them when I put the engine back together recently - but chickened-out, and made some new long brass nuts instead.
Nice idea Alex.
Perhaps the head being prepared for the tall block engine should be fitted with Helicoils so that I don't waste the money spent on the cap screws.

Well.... You know how my other love of fixing things led me to rebuild errr... a 'few' Lambretta scoots..Yes?? Well on the chaincase/crankcase/gearbox unit there are about 20 x 7mm (yes 7mm) studs scattered around the thing most of which get the threads pulled out after a while. My 'fix is to do away with the studs and helicoil the holes to 8mm then (in the interest of originality) make up some 7 - 8mm studs with the 8 screwed into the case and the studs taking the standard 7mm nuts.. But you can also use 8mm socket caps to hold the thing together, and with the outer cover holding the kickstart, the stronger the better. You get much better torque on the helicoiled holes than you do the std threaded ones. Result? A more rigid assembly!

Now is that not a good thing on our twincam engine's exhaust flanges? I think so.. Rohan / John... ??

The other big advantage is working on the engine.. Fitting, Cyl head working, removal of the Manifold etc...MUCH easier with the studs out. Don't you think so?

If one is going to do this,(I have not done so as of now on the Sprint's head) one can obtain helicoils or recoils up to twice the diameter length. Use them.. So for say 8mm caps screws you have 16mm long inserts (for E.G.) Or of course the imperial equiv'.... 5/16'' unf.. = 5/8'' insert length.. Don't drill the holes any deeper!



Alex....

alexblack13 wrote:Well.... You know how my other love of fixing things led me to rebuild errr... a 'few' Lambretta scoots..Yes?? Well on the chaincase/crankcase/gearbox unit there are about 20 x 7mm (yes 7mm) studs scattered around the thing most of which get the threads pulled out after a while. My 'fix is to do away with the studs and helicoil the holes to 8mm then (in the interest of originality) make up some 7 - 8mm studs with the 8 screwed into the case and the studs taking the standard 7mm nuts.. But you can also use 8mm socket caps to hold the thing together, and with the outer cover holding the kickstart, the stronger the better. You get much better torque on the helicoiled holes than you do the std threaded ones. Result? A more rigid assembly!

Now is that not a good thing on our twincam engine's exhaust flanges? I think so.. Rohan / John... ??

The other big advantage is working on the engine.. Fitting, Cyl head working, removal of the Manifold etc...MUCH easier with the studs out. Don't you think so?

If one is going to do this,(I have not done so as of now on the Sprint's head) one can obtain helicoils or recoils up to twice the diameter length. Use them.. So for say 8mm caps screws you have 16mm long inserts (for E.G.) Or of course the imperial equiv'.... 5/16'' unf.. = 5/8'' insert length.. Don't drill the holes any deeper!



Alex....

Rohan is already a convert, advocating the use of Bolts rather than the Studs for ease of maintenance.
From practical experience, in optimum conditions, threaded Holes in Aluminium will start stripping their Threads after ~ 7 applications.
I mentioned that Studs are the "Engineering" solution, not necessarily the most practical one.
As a rule of Thumb design guide the accepted norm for threaded Hole depths in Aluminium is 2 x D
i.e. for a 5/16"UNF min. thread engagement = 5/8" (as you mentioned)
This length of engagement my be reduced when using Helicoils due to the higher integrity of the S/Steel Insert.
I'm not certain of the Twincam Manifold Stud threads; I suspect them to be 5/16"UNC?
If so, when Helicoiling it may be possible to insert 5/16"UNF inserts & fit more commonly available Socket/Cap Head Bolts, which have far better self locking Geometry/ability.

Yes me too john. I would helicoil to UNF (Or metric fine)...Easier to get the fasteners also methinks...

I fitted my exh' manifold to the car with the engine in but no manifold studs fitted. They went in through the manifold flange holes. I gave the gaskets a coat of silicone sealant also...

So far so good.

Alex....

D.J.Pelly wrote:From practical experience, in optimum conditions, threaded Holes in Aluminium will start stripping their Threads after ~ 7 applications.

So I guess I should Helicoil the plug holes too!!!!!!

From memory, the length of the standard Helicoil is 1.5x diameter.

As an apprentice in the good old days I was taught that all threaded holes should be 2x diameter.