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1. Prepare yourself! Changing manifolds can be a little dirty and may take an hour or so to do.


2. Ensure you will have the correct tools to do the job. Have you got the correct spanner size or wrench size sockets? Do you have a scraper to remove old gasket material from around the mouths of the cylinder head exhausts? Old cast iron manifolds and risers can be very heavy- do you need somebody else to help you lift them out? Changing manifolds is also an excellent time to replace spark plugs and check engine compression.


3. After you have removed the old manifolds examine the extractor entrances. If they are nice and clean then there is probably no problem, but if you see signs of water, rust, corrosion or anything else that seems out of place, it could be a sign to inspect further. Look inside each exhaust outlet on the cylinder heads- do you see any corrosion or rust? Do they all have the same appearance?


4. Remove all the spark plugs. The spark ends should be characterised by a light brown chalky colour. If they are wet or appear rusted, then water, either salt or fresh has entered the cylinder at some stage. If you have a compression gauge, remove and ground the HT lead from the coil, have somebody turn over the engine at least four revolutions (it is a four stroke engine after all!) and write down the compression. Look in your engine owners manual for the correct compression rate. Do the readings for each cylinder approximate this figure?  As long as all the cylinder pressures are within say 20psi or each other, there is nothing major wrong. A very low compression may indicate worn cylinder rings or improperly seating valves. Unfortunately this generally calls for major engine surgery.


5. If you have not already realised, your manifolds might come in two or even three sections - the manifold section and the riser section. This is because many boats, such as ski boats, have a straight through wet exhaust that exits via the transom or from an open engine configuration and as such do not need a riser.


Risers are used to raise the level of the exhaust water above the water line of the boat so as to ensure no sea water flows back into the engine via the manifolds. In effect the exhaust is channeled along the manifold and up into the riser and then downwards where it is mixed with the raw water and through to the exhaust.

If your boat uses risers, you will now need to bolt the components together.


Place the exhaust gasket between the manifold and riser and bolt securely together. It is possible to use a sealing compound, however check that it will not deteriorate the gasket.   Use an anti seize compound when tightening all the bolts.

You are now ready to attach the manifold to the engine. Coat the manifold attaching bolts with a non-hardening substance such as gasket maker. Gasket makers are useful if some bolts screw into the internal water compartments such as on a Chrysler 318 engine. Hence they will not rust, seize or leak. Loctite produce a range of suitable anti-seize products for this purpose.

After you have tightened all the bolts, ensure the exhaust is secured. It is now time to connect the plumbing. Depending upon your engine, you should be able to use your existing hoses. 


6. Double check everything! Did you loose any cooling water when you removed the bolts- if so replace the water/cooling fluid. Check the oil. (If it shows milky streaks then there is water in the oil.) Ensure bellows and hose pipes are secure. Start the engine and listen for the water pump to fill the manifolds, risers and flow out the exhaust. The engine may sound different your new manifolds. Run the engine at fast idle until the engine is warm- look for leaks or anything else that seems out of place. Turn off the engine and retighten all the bolts and hose fitting while the engine is warm.


7. You are ready to go! Enjoy worry free boating!


Installation Checklist

bulletHave necessary tools- wrench, spanner, compression gauge, extra helping hand
bulletUsing gaskets, bolt together the manifold, riser and riser extensions.
bulletRemove the old manifolds- careful they may be very heavy to lift.
bulletCheck around exhaust ports for corrosion or damage. Inspect old manifold intake ports for corrosion.
bulletOPTION: Remove old spark plugs, conduct compression test (ground coil HT wire), install new spark plugs.
bulletApply anti-seize material to the manifold had bolts and bolt manifold to cylinder heads. Secure exhaust pipes to manifold and hoses to manifold and between manifold and riser.
bulletRun engine until warm. Check for leaks. Retighten all bolts.
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