Exhaust Manifold

[Saddletramp]

Water is getting into the bores on my Volvo MD2b. I suspect the manifold though it looks okay. How is it constructed, do the water ways run through a jacket before mixing with the exhaust gases.

If so I suspect one of them may have corroded through allowing water back through the exhaust port.

[image]

[/image]

 

[VicS]

The manifold is pretty heavily constructed and although not impossible I would have thought corrosion of it would have been one of the least likely ways in which water could enter the cylinders.

Incoming water enters via a T piece on the under side and flows via two small passages to the cylinder heads. Water leaving the heads flows via other passages to leave the manifold via the thermostat at the front end where it joins water flowing though the bypass in the thermostat cover. The total flow is then via the external pipework and the anti-syphon valve, if fitted, to the injection point on the exhaust outlet bend at the rear end of the manifold.

Sources or water ingress could be a defective head gasket or a defective manifold gasket. If you have an anti-syphon (or vacuum) valve (and you should have unless the injection point is significantly above the water line level) it may be blocked and not breaking the syphon and so allowing water to syphon in and fill the exhaust system.
Another possibility, I understand, is corrosion of the cylinder liners close to where the cylinder water jacket drain cock is situated.

You may find THIS DIAGRAM helpful but it does show various options that may not apply to your installation.

If you have an anti-syphon valve check that first.

What is the evidence for water entering the cylidners and is it both.

BTW dont be fooled by what looks like another water connection from the thermostat cover, below the thermostat, to the manifold. It isn't, except on the MD1B where it is the water inlet to the manifold.

 

[Saddletramp]

Vic the symptom is bent pushrods and broken cam followers on the front cylinder. This has happened twice know. The general consensus seems to be water in the bores.

I do not have an anti syphon thingy. Did not know they existed till I saw the diagram you attached. Thanks for that. I thought the external pipe was just a bypass, did not realise it carried the main flow.
The previous engine, an Md2, did not have an anti- syphon.

The manifold is a long way above the water line and drops into a trap so do not see how it could syphon back. Having said that something is wrong so it could be the cause. It happened on the same cylinder last time as well. It could be a distorted head. Did not have it ground last time. Be nice to find something conclusive before I rebuild it again.

 

[VicS]

I would not have expected water in the cylinders to have caused bent push rods and broken cam followers, but it would be interesting to hear other views. I would have thought piston and conrod damage would have been more likely, or just the engine water locked and wouldn't turn over on the starter.

Fair enough about the antisyphon valve. If the exhaust injection point is well above the waterline level (recommended figure is 6") there is no need for it. Had to mention it because sometimes the first people know about them is when they have failed to open and their engines fill with water!

If you had been getting water in the bores you should be able to find it in the engine oil. I think I'd be wanting other, direct evidence of the water if you see what I mean.

If you can find that other evidence then fair enough and having ruled out syphoning into the xhaust as a likely cause its back to the possibility of gasket failure or a distorted head but while it is off do check that manifold though. You should be able to check the integrity of the water passages without too much trouble. The inlet ones as i said run from the T connection in each direction, one to each head, while the outlet one runs from the two heads to the thermostat housing. The drain valve is on one but off hand i cannot remember which.
There could be a crack in the manifold is suppose, frost damage maybe if it has not been properly winterised.


If you cannot find any direct evidence of water ingress I'd be looking for mechanical reasons. One thing I would check is the oil feed to the rocker shaft, we had one of the pipes break off at the top banjo, but we did not know until we found it while taking the cylinder blocks off to unbung the waterways.

Sorry a few ideas perhaps but not a not of positive help. Keep us informed.


other diagrams and parts lists on This Link

Workshop manual HERE if you need it.

Operators manual via This Link if you dont have one. Just enter the engine type, MD2B thats all.

 

[Saddletramp]

The only other suggestion for the bent pushrods was sticking valves. But they open when turning the engine by hand. I would have though if they stuck enough to do that kind of damage they would be seized solid. So water seems to be the favourite. Though I saw no evidence when I stripped it last time. Having said that it would only take a tiny amount, doubt it would be seen in the oil.

There appears to be plenty of oil at the rockers. It seized on firing up so not enough time to suffer from lack of oil.

As you can see from the photo the waterways look okay in the manifold. Frost damage is possible, the engine was stored outside winter before last. Thought I drained it, and we did not have a hard winter. It could have been swapped at some point as well as the engine was in a boatyard for some time before I bought it.

Typical I had just got it all wired up, moved the ignition panel inside. A few hours running and bang.

Thanks for the comprehensive answer and links.

Will keep you posted.