I'm into a D2 5U engine, found that the intake manifold has been drilled about 5/16" opposite every cylinder head port. Yup, you understand that correctly--a hole over every port to be sure dust got into each cylinder equally, unless there was some attachment that I've never heard of that plugged these holes. Any ideas, anyone? It was a pony start tractor, but could these have been glow plug heater holes? They arn't threaded. I sure never have seen anything like it before...

Jack

I never saw or heard of a manifold being drilled like you described. Maybe someone did this for a reason after they got the tractor but all the glow plugs I ever saw were up in the precombustion chamber along side the fuel spray nozzles.If they are open to the inside of the manifold then yes you can,t let it go like that as it will suck in dirt & dust from the outside atmosphere. Either repair the holes or I,d look for another manifold.

Jack, I have two later D2 5U's that have holes in the exhaust manifold, not the intake by each port on the bottom. There more like 3/16 or smaller. I think they are moisture drains.

Nope,
Thats a new one on me. Was the air/exhaust heat exchange tube intact?
Somebody embarked on air heaters, water or fuel injection????? Who knows:D
Any other strange plumbing on the engine???
5/16 is tap hole for 3/8 NC thread??????

Why not just tap and thread the holes and turn in a short bolt to plug them.
easy quick and safe compared to welding or looking for a different manifold.

D.K. in S.K.

OK, Thanx guys. Maybe I have seen everything now!

The engine was a take-out, I never saw the pipe from the air cleaner. I don't know what might have been there other than standard.

I came to the same conclusion--easiest & best to tap and plug or get another manifold.

I saw air plenum heater on Onan air-cooled diesel engine, but it was nothing that would go through such a small hole. It heated enough air for about two cranks over. I don't think that could be it either.

Hi Jack,

I think threading it is a good idea like Manx Kat suggested. You get to keep your original mani. and there's no cost. I like keeping things O.E.
The 5/16" holes are almost perfect to accept 1/8" NPT pipe plugs. Drill size is 8.75mm or 11/32" .(0.3438") ..which is one size up. Use socket head (allen) type plugs which will be flush when installed..no ugly bolt head sticking out, which you can fill small hex hole too with JB weld so you can't see the plug anymore. Just a thought. Very sexy repair;) . Put lock-tite on theads too.
Hope this helps and good luck!

Ex-Jaguar restorer Ken

Just wondering if the holes could have been for some sort of ether injection for cold starting. I'm pretty sure they offered such an option but i've never seen one so no idea of how they were ported. Personally I would have thought a single injection point farther up the air flow but just a guess. Pete