MD7A Question

[DaveCD28]

Hey guys,

I pulled the cylinder head off my MD7A to replace the head gasket and am cleaning it up a bit before I put it back on. I have a lot of experience completely rebuilding gasoline car engines but this is my first Volvo, and my first diesel.

It appears from the condition that the rocker assembly is not getting lubrication, and I cannot for the life of me figure out how the rocker assembly/valve train gets lubricated. The only thing I can deduce is that the oil passage from the camshaft on the side of the head somehow is supposed to feed oil to the rocker assembly. It looks like it leads to the rocker mount stud, but there is no hole in the stud to allow oil to get into the rocker arm assembly. I have not removed the stud at this point so do not know if the oil passage bypasses the stud or is supposed to enter it.

Does anyone have experience with the MD7A cylinder head and know how the rockers (and lifters) get oiled?

Thanks,
David

[moctrams]

I would talk to Vosbury Marine & Recreation Inc in Annapolis, Md. They can give you good answers.
410) 757-3844

303 Greenlee Rd

Annapolis, MD 21402

[Maine_Buzzard]

Wow, worthy of a Cartalk Puzzler Award.

There is a 4mm galley running up from the block, near the front cover that turns towards the forward screw for the rocker arms. It must percolate around the threads, because there is no hole in the stud that I would expect. It then fills the hollow rocker arm shaft and splash lubes the valves and tappets. No O ring, no seals.

Some very clever Swedes there... I was expecting that the tappets would be hollow and then splash up through the adjusting bolts. (A la the VW bug with hollow pushrods.)

A lack of lubrication is likely low oil pressure or superbad sludge in the rocker arm shaft.

[barfwinkle]

You know, you have to absolutely love this web site!

Fair Winds and Merry Christmas

[DaveCD28]

Maine_Buzzard: Thank you, your thoughts appear to be correct.

Going on your suggestion of the thread idea, I blew compressed air through the oil passage from the bottom of the head and got nothing. So I removed the stud, which was frozen in place due to rust. Then I blew the air again and it flowed freely into the hole from where the stud came from. So I cleaned the stud's threads and chased the hole, then threaded the stud back in and blew the air into the passage again, and the air flowed freely around the threads. I assume this is the path the oil will take to the rocker assembly.

This brings up a point for others to consider:

It appears the problem was that I got water in the oil from the leaky head gasket. Well, being that it was in the oil it of course flowed with the oil through the engine and, being that it was salty water, it appears that it caused the stud to rust to the head, effectively blocking the lubrication path to the rocker assembly.

So if you ever have a blown head gasket or otherwise get water in your oil, make sure the rocker stud threads are clean of rust when you fix it.

-Dave

PS: Incidentally, there was no sludge and the rocker arm shaft was completely clean.

[CD_Sailor]

Maine_Buzzard: Thank you, your thoughts appear to be correct ...

Kudos to all writers to this thread. My first line of defense would have been (and has been for decades) to call Richard Vosbury at Vosbury Marine and, if necessary, buy him plane tickets to my boatyard. In lieu of that tactic, the explanation presented by Maine_Buzzard was right on the money and quite slick. Keep it up.