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1942 D4 pony refreshed ton of blowby :/

CamaroMan

Member
Joined
Jan 25, 2022
Messages
19
Location
Long Beach, CA
Well new to me D4 pony threw a rod cap 3 weeks back. So i tore into it polished crank turned new main bearing on lathe. Replaced bad rod. New bearings and seals rings etc.

Hined bores with 80 grit and gapped rings lapped valves. I budengines army shop so not new to this.

Set valve clearance carb was redone. It fores right.up but I'm somehow losing oil andthere is some super bad blowby..

When I checked rings I shone a light from behind and saw nothing so assumes they would seal well.

Plugs are tan.

I also cut the slots in the manifold gasket ..

1737431318318.png
 

Joe H

Senior Member
Joined
Nov 28, 2023
Messages
559
Location
Utah
Not that I know anything about this, but you've got a picture there of the manifold gasket on a diesel engine, but you say the carb was done and the plugs are tan.

So gas motor or diesel ?

Joe H
 

CamaroMan

Member
Joined
Jan 25, 2022
Messages
19
Location
Long Beach, CA
Not that I know anything about this, but you've got a picture there of the manifold gasket on a diesel engine, but you say the carb was done and the plugs are tan.

So gas motor or diesel ?

Joe H
Check top pic: it says starting engine, the lower gasket is for the main engine. Its gas -
 

CamaroMan

Member
Joined
Jan 25, 2022
Messages
19
Location
Long Beach, CA
So what's the manifold gasket info have to do with it?
not sure if that has sth to do with the blowby - i doubt it but just confirmed that I did follow the updated design. far as i could tell all that seals is crank gas basically - should not have anything to do with blowby but maybe i missed something.
 

CamaroMan

Member
Joined
Jan 25, 2022
Messages
19
Location
Long Beach, CA
joe i think the document is specifying the STARTING engines ON those diesel models as there is no model number on the starting engines no. Read the 1st sentence - it states "starting engine con rod failure".

Besides that upper gasket is IDENTICAL to the starting engine manifold gasket -
 

bccat

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Joined
Jun 12, 2010
Messages
368
Location
Langley B C
Occupation
Retired millwright,Heavy Equipment Operator
joe i think the document is specifying the STARTING engines ON those diesel models as there is no model number on the starting engines no. Read the 1st sentence - it states "starting engine con rod failure".

Besides that upper gasket is IDENTICAL to the starting engine manifold gasket -
I understood what you were saying from start. Thinking rings are not broken in yet. Too much oil in the crankcase , what oil weight are you using ?
 

CamaroMan

Member
Joined
Jan 25, 2022
Messages
19
Location
Long Beach, CA
I understood what you were saying from start. Thinking rings are not broken in yet. Too much oil in the crankcase , what oil weight are you using ?
lucas 30 weight break in just cos i have it lying around - man i build alot of engines this is nuts. i thought maybe sth in the vent system was weird- rings did seem a little dodge but overall they went in fine and i gapped them chamfered the edges bla bla bla.

This thing was CLAPPED out and ran fairly well before it threw the rod cap out 180 degrees..
 

CamaroMan

Member
Joined
Jan 25, 2022
Messages
19
Location
Long Beach, CA
there is also a whine in motor and i think there is maybe not enough lash between the ignition unit gears- might have to pull intake manifold which means pulling motor cos i dont think you can get a good seal against main engine without tilting the pony back to slip seal in-

should have bench ran this b4 dropping it on. luckily all the hard work is done and it shouldnt be too hard disassembling- ill do a comp test today-

as mentioned i did shine a flash light behind rings and didnt see anything past ring and bore surface so figured it shd be ok-

ring quality was very below average-

anyway it had 80 grit hone job pretty rough sure those rings should have started breaking in- ill do a few more runs and see if it starts improving otherwise ill yank and recheck and order other rings.
 

chidog

Senior Member
Joined
Jun 21, 2021
Messages
1,066
Location
kent, wa
How many hours since this overhaul? I'd be guessing the rings are all worn down due to that rough road in the cylinders. .

Curious, why the lost rod cap? Bolts not tight?
 

CamaroMan

Member
Joined
Jan 25, 2022
Messages
19
Location
Long Beach, CA
oh i ran it yesterday for the first time- rings that came out were pretty bad (see pic) but it actually still kind ran ok- less blow by than now! dam this thing is spitting oil out the top. I might have over filled so will check later when i get down to the shop.

one cylinder had zero valve clearance. i thought spec was 12 thou but after setting to 12 (well that involves grinding the valve stem!) found online docs that spec it at 8 thou.. oh well little less compression. I guess i can reweld with 7018 / oil quench and polish back down for 8 thou if i have to go back in.
.
the split pin came out and nut backed off is my guess. it got toasted.

I blue loctited mine and put in all new split pins so they not going any where.. it was carnage

this was the ring gap b4 tear down- rod cap looks completely redesigned-
 

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Welder Dave

Senior Member
Joined
Oct 11, 2014
Messages
15,007
Location
Canada
Check top pic: it says starting engine, the lower gasket is for the main engine. Its gas -
Both pics. are for starting engine gaskets as per the last paragraph. One for 4 1/4" bore 6 cylinder engines and the other for D17000 engines. I don't get all the confusion?? It's pretty clear 1940 english to me.
 

chidog

Senior Member
Joined
Jun 21, 2021
Messages
1,066
Location
kent, wa
Split pin ? Do you mean a cotter pin, AKA cotter key, other pins that are split are roll pins.
I'm a nomenclature person.
 

TomA

Well-Known Member
Joined
Aug 17, 2012
Messages
165
Location
Mariposa, CA
Mag shaft breakage is usually caused by too much end play in crank usually caused by locating pin problems in front main bearing. There are alternatives to end play control discussed on ACMOC requiring machining.
 

CamaroMan

Member
Joined
Jan 25, 2022
Messages
19
Location
Long Beach, CA
I machined a new crank bearing on the pulley side and reused the flywheel bearing as it was ok.. I added material to take up the end play it's down to about 15 thou now..

I'm thinking the combination of tighter tolerances stacked up paired with possibly a ightly thinner manifold gasket (unconfirmed) led to too much gear load.. mag did slide in but teethhad almost not play so after heating up it probably tightened up and fatigued the shaft.
 
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