2 Valve or 4 Valve

[spartonboat1]

Any general knowledge out there about whether my 1972 6-71N was a 2 valve or 4 valve head engine. When I re-build, the tech assumption is that it will be a 2 valve, because he is preparing a 4 valve head for an "upgrade". So is it fair to assume that at this age of engine, it is a 2 valve head?

 

[tpld3]

Wouldn't the N mean that it's the newer four valve?

Perhaps this will tell you more:

http://2cycle.mtu-online.com/index.php/extras/engine-model-number-decoder

 

[Will]

Why doesn't your mechanic pull the valve cover and look?

Of course the next question would be if the extra expense of doing a 4 valve head is worth the performance boost. Or, would there be other advantages?

I think the "N" indicates "Natural" as opposed to "TI" for "turbo/inter cooler".

Will

 

[RT46]

671N is a naturally aspirated diesel and usually has the two valve heads

the 671 TI and TIB are 4 valve per head

 

[yachtsmanbill]

I seem to recall mostly pumps and generators are 2 valve units. ws

 

[RT46]

correction.....

should say:

671 TI and TIB are 4 valves per hole.....not "4 per head" sorry for the typo

 

[yachtsmanbill]

The venerable 1948 6-71N 180 hp model in a USACOE tugboat. ws

 

[spartonboat1]

I briefly overheated the stbd engine several years ago, so we pulled the head. Thankfully no issues evident and was observed by both the tech and a surveyor. However, a different tech mentioned, at another time, that the stbd engine appeared to have an upgraded headed, probably from when it was majored in 1996, before I bought the boat.

I will contact the tech that pulled the stdb head, after the overhead and ask if he remembers if it was an 2 or 4 valve head. Pulling the valve cover is the other approach, although I have an old tin cover, so I'd hate to go through getting it reset and resealed, since had trouble with that before.

 

[captddis]

It should be four valve on your engine.

 

[tpld3]

671N is a naturally aspirated diesel and usually has the two valve heads

the 671 TI and TIB are 4 valve per head

Not all four valve engines were TI configurations. I had one of the newer 671 engines with four valves with 250 HP, I think they called it a high block, that was naturally aspirated.

The design of the 671 was pure genius for the time, or any time for that matter. It really is astounding how many configurations there were for this engine.

I replaced a pair of Cummins 300M, one of which got a bath, with a pair of 671 two valve engines in a 50' steel trawler. It was cheaper to buy two used 671 engines and marinise them than to rebuild one Cummins. I had to reverse the direction of one of the 671's so I did alot of research and it was surprising how easy it was to do. I was fortunate to find an old mechanic that knew which plugs to change for the oil passages on the end of the block. I don't remember how many parts guys and mechanics I talked to but this old timer was the only one that mentioned changing the oil plug location. This was in 1996 and those engines are still running well today.

 

[newinlet]

1978 j&t. 310hp 671n. 4valve head saw them with my own eyes. As I recall