Subject: Rusty manifold on a BMC 1.5

Hi Tony,

The exhaust manifold ( I think that's what it's called- it's a long rectangular block on top of the engine, with pipes coming in from each cylinder plus the cooling water in and out) on my 1972 BMC 1.5 is rusty where 4 pipes join from the engine.

Does this imply overheating? Is it anything to worry about?

Can it be re-painted? Do I need special paint?

Is it a it job to replace if it goes?

Many thanks in advance.

Mr R M

ANSWER

Dear Mr R M

I ignore the conditions you attempt to apply by the footer on your mail. If you wish to apply them please delete this email without reading the rest of it and inform me immediately. A paid for confidential service is available, the free advice is intended to help all boaters and as such questions and answers may be reproduced in any number of other media and places

As long as the exhaust manifold (yes that is what its called) is made from cast iron you have absolutely nothing to worry about..

There is a possibility that someone has fabricated it from mild steel and welded it together, so look at it and see if the edges of the "box" are welded or rounded with the same dimply texture found all over the rest of the painted surfaces. I do not think it likely, but if it is mild steel I would advise you to get a cast iron one with some urgency (probably cast aluminium nowadays) because if it rusted internally you would end up with engine damage.

Those four "pipes" duct the hot exhaust gasses (probably well over 500C) to the manifold from the cylinder head. They always get their paint burnt off as soon as the engine is put under load, so ignore it. If you feel you must paint them, wire brush off the "pipes" and apply "stove paint" (any colour as long as its black), but you really do not have to bother.

If the brighter rust you find at the start of the season worries you then spray them with any form of oil or spray grease when you lay it up, but expect clouds of smoke when the engine runs. Come to think of it, you are likely to get smoke and a burning smell if you insist on painting the "pipes".

In the unlikely event of a cast manifold failing - they normally only fail if you let the water inside freeze - it is the four nuts holding the exhaust outlet elbow onto the manifold & lift the exhaust pipe free, two nuts on each "pipe" (3 "pipes" on the exhaust manifold - the inlet manifold is a separate item, but may require removing so a new gasket can be fitted) and then undo the hoses/water joints. If its an old direct cooled engine some of the solid copper pipes have very fine threads on the unions so take great care when reassembling them.

Hope this helps

Tony Brooks

Subject: Seized Motor

Tony,

I have a 1986 Volvo Penta Inboard/Outboard Motor. The boat has been sitting not running for about 5 years. I have tried to start the motor but it is locked up tight. It was running when parked. I have tried transmission fluid and diesel oil in the cylinders on advice from friends, but cannot get the motor to turn. Is there anything that will dissolve rust and get this motor turning again? It has low hours and should fire right up if I can get it to spin again. Any advice would be greatly appreciated.

Brian D

ANSWER

Thank you - at last a US email that is polite and makes sense, so I will break my "delete all US email" rule and try to help.

I do not know why anyone should think diesel or transmission fluid would be very much help.

First remove the alternator drive belt because seized alternators will stop the engine turning over.

You also need to ensure that it is not the transmission that has seized. I suspect that if you can turn the prop when in neutral we could assume it is likely to be free.

Next remove the injectors (I bet its a petrol engine!! - so spark plugs) and get hold of what we call penetrating oil in the UK - "Plusgas" is a brand that sounds as if it originated in the USA). Pour plenty down each cylinder and leave it for a week, putting a little more in each day. (Its main use is freeing rusty nuts and bolts.)

Now remove the starter motor. This gives you access to the flywheel teeth. Use a very large screwdriver or other suitable lever between a tooth and one side of the starter hole to try to start moving the engine - first a little one way, and then a little the other. Use the longest lever you can, but do not snap a tooth off.

If that does not work take the thermostat housing off and ensure the block is free of water. Boil several kettles of water and pour the boiling water into the block, but the kettles back on and when boiling, drain the block again and refill with boiling water. Do this a few times until it is uncomfortable to put your hand on the block. This will expand the cylinders and may help the proceeds - go back to trying to lever the engine over.

This is likely to be a long process and even when you succeed in freeing the engine, there is still the question of the piston rings being free enough in the pistons to give compression to start the engine and to allow it to run well. I must caution you against the following, but in dire emergencies I have persuaded diesels with low compression to start by disconnecting the alternator and any other electronic equipment and then using a domestic battery to give 24 volts for starting. If you do this and burn something out its your own fault!

I fear this may end up as a strip down, but if you do free it, remember to change the oil before you have run it for long to remove all the stuff you have been putting down the cylinders - much should have drained into the sump.

Hope this helps

Tony Brooks