JD 70 Exhaust Manifold Changeout

I need to change the exhaust and intake manifold on my 70 Standard 2 cyl. JD. I know the bolts will be rusted and set in rather tight after many years. Does anyone have any pointers on how to best remove the bolts without causing damage or possibly turning them off? I heard years ago that one way to help in doing this is to take a center punch and tap each bolthead and this would help.

Thanks, dwb

1st of all, don't even think the exhaust bolts are going to turn out..!!
Yes, tapping with a small brass hammer and using plenty applications of penetrant will be needed..
Don't twist any of them off, if you don't like drilling and taping..!!
Get the exhaust bolts to loosen by repeatedly taping with the small brass hammer and using penetrant, until they appear loose all the way down to the head..DON'T twist them off..
Now, if they will turn out..you can try it--with CARE..
If not, you will need to cut the stuck bolt-heads off and remove the rest..
Raise the manifold up as far as it can go and cut the rest of the bolts off, leaving as long of stubs as possible..
Remove the manifold..
Heat the stubs RED hot and while still somewhat red, tap them on the end with a medium palpein hammer..
This will break the rust loose in the head..
Let them cool and they will screw right out with a pair of Vise-Grips..
If the exhaust gaskets have been blown-out very long, the head will still need to come off and need machined flat, or the new exhaust gaskets will never "hold"..
Sorry, but you "asked" how to get it done...!!
Take your time and work Patiently...!!!!

Ron.

If your bolts have washers under the heads cut these out so you can get penetrant to run down the bolts.

Most of these I have done were so far gone the right hand side gaskets were also blowing due to the cyl. head being erroded away. So I just pull the cyl. head,remove the bolts and manifold and if any bolts twist off I just drill them out when I have the head set up in the milling machine to resurface the maniflod gasket surface. Then I also do a much overdue valve job. Very seldom do you find one not in need of some valve work.

Do you have a gas or a diesel? If it is a gas, yea then the info given below could be your future. But you said you had bolts holding the manifold on, that means it isn't original. Unless you mean studs and nuts. If you are lucky it has been off not to many decades ago and someone put the manifold back on with bolts instead of studs. And if they went to the trouble of replacing the bolts, maybe you will get lucky and they gobbed it up with anti sieze at the same time.

The numbered series did use bolts for the manifolds from the factory. Lettered series did use the studs.

Thanks much Ron, sounds like this method might take away the necessity of removing much of the parts located above and around the manifold as well (raising fan shaft, removal of water piping, etc.).

dwb

Thanks Mike, I don't think they have washers on them (I am currently out of country) but will take all of this advice to heart.

dwb

Thanks, it is a gas model and does not have studs.

dwb

If the bolts will come out the manifold will slip right out from under the fanshaft and water pipes. No need to remove them.

Pull the head and change the maifolds on the bench.Odds are the head mating surface has erroded over the years and must be milled flat. Or the new gasket/manifold will not seal.
It's an oportunity to check bore wear and inspect valve guide/stem clearance. And maybe even install hardened exhaust valve seats.

I have changed several manifolds on different models of 2 cyls. On 70's and 720's I have never been able to remove the manifold without removing the head. On 50's 520's, 60's and 620's yes, but not the 70. Also the bolts are usually rusted halfway through, so, they always break. Usually the surface needs resurfaced anyway.

Thanks for all the information, really useful.

dwb

Thanks Mike, really appreciate the information.

dwb