6.2l bore clearances

[Bojangles]

Rebuilding a 6.2l. The bores had some pitting which was probably caused by water in the oil. Engine has been sitting for a long time.
I honed all the cylinder bores and the look good.
I then measured the bores and found that They exceed the maximum bore size tolerance.
The pistons are standard and within tolerance.

Measurements of the oversize are below.
No 1 0.945 Thou
No 2 2.52 Thou
No 3 0.945 Thou
No 4 3.701 Thou
No 5 3.307 Thou
No 6 3.701 Thou
No 7 5.26 Thou
No 8 0.157 Thou

My question is is it ok to run the engine with the above parameters?

My thoughts are that the only real worry is the 5.26 thou No7 cylinder bore

Thanks

[DmaxMaverick]

If your figures are simply the overbore of standard pistons, they need to be bored, and oversize pistons used. If you were able to "clean up" pitting with a hone, then they weren't pitted. If they were pitted, and you honed (excessively) until they weren't, the cylinders aren't round or straight. Good luck getting new rings to seat. Honing is no substitute for a proper bore. A hone is intended to only scuff the surface to allow oil adherence, and should never change the diameter. They need to be properly bored to get squared up. Numbers 4-7 are concerning.

If your figures are overbore of the maximum bore diameter, then they are out of acceptable range. Either scrap the block, or run what you have. New rings won't likely seat, so prepare for a lot of blowby. Toss a coin, or cut your losses. I've seen acceptable results with a worse start, but that's an exception, not the rule.

[Bojangles]

Thanks for your advice.
Looks like I have 2 options.

1. Bore it and fit oversize pistons.
2. Buy a new block .

Can anyone advise where to buy a new block?

Thanks

[DmaxMaverick]

New blocks are pricey. Optimizer or P400 6.5's is it. Navistar castings and AM General builds. 10 grand plus, but it will likely outlive you. If your block is good otherwise, there's no reason to not bore/oversize it. It isn't that big of a deal, no more than any other big block build, and parts are still available at reasonable prices. Check it for cracks and such, and source some Navistar heads, Navistar forged or Scat cast steel crank, Fluidampr balancer, and make a good one. Not cheap, but you already have cheap, and it ain't moving.

A couple members here recently did stock-like 6.5L rebuilds (in the 6.5L forum, Arveetek and More Power), and posted them. Read them, for starters, and get a feel for what's ahead of you.

[Robyn]

Stock bore size on a stock 6.2L diesel is 3.98" (These are metric engines)
Piston to cylinder wall clearance can be quite happy in the ,003" to .004" ranch
Even .005" between the cylinder and the piston will not be terrible......

Factory was around .002"
I am not a fan of that tight on these engines...

[Robyn]

AS Maverick said.
Get the block tanked and magnafluxed for cracks
Bore to .020" oversize or even .030"

I am looking at your numbers ?????
What is the exact bore size on the cylinders
What are the exact clearances between the pistons and the cylinder.

Post those numbers please and lets just see what you have before we start spending the $$$$$$$$$$$$

[Bojangles]

The following sizes are from the army service manual.
Cylinders 100.990 / 101.066 (3.976'' / 3.979'')
Piston clearance cylinders 1 to 6 0.0889 / 0.1143 (0.0035'' / 0.0045'' )
Piston clearance cylinders 7 and 8 0.102 / 0.127 (0.004'' / 0.005'' )

The following are sizes as measured
No 1 cylinder 101.09 (3.98'')
No 2 Cylinder 101.13 (3.981'')
No 3 Cylinder 101.09 (3.98'')
No 4 Cylinder 101.16 (3.982'')
No 5 Cylinder 101.15 (3.982'')
No 6 cylinder 101.16 (3.982'')
No 7 Cylinder 101.20 (3.984'')
No 8 Cylinder 101.07 (3.978'')

Piston diameter 1 to 6 100.9 (3.972'')
Piston diameter 7 and 8 100.85 (3.9704)

Once again I appreciate your help

[Robyn]

Looks decent.

What sort of shape are the pistons in ????
Now
What sort of vehicle is this going in an whats it going to do ???

If it were my call.....Clean the block well and check the main line area (Around the bolt holes and main webs for cracks) If no cracks......Good deal

If the crank bearing journals are good....Fresh bearings (Clearance about .0025")
Pistons look decent ?????

Toss in a fresh set of rings.....DO NOT USE CHROME OR MOLY RINGS ON THIS BUILD

Standard cast iron rings.....
Felpro head gaskets and a fresh set of head bolts ....

Are you going to grind the valves ??
Make sure the pre cups in the heads are not sunk into the heads

IF THE BLOCK IS CRACK FREE.....This old girl is not perfect but should run fine.

Pictures of the cylinders and pistons would be nice....Crank pics too..

[Bojangles]

The pistons are in very good condition.

The engine will be going into a 28 foot boat. It will be marinised and be fresh water cooled via heat exchanger.
The duty cycle of marine applications varies from idle (600 rpm) Cruising (2000 rpm) full throttle (3600 rpm).
Typically engine starts and idles until open water is reached. Cruising speed is normally 80 Percent of the time and can be anywhere from 1 to 10 hours.

Full throttle mainly used in emergencies.

Crank bearings need replacing. Main bearings are ok.

Valves will be ground.

Pre cups are not sunk into heads

I will send Photos when I work out how to do it.

Thanks

[Robyn]

Sweeeeet
Polish the crank likely a good idea.
What sort of shape is the cam in ????
Was the oil decent or did it show signs of water contamination ??
If the cam is in good shape ...Just replace the lifters..

The bearings on these engines were select fit and you may find the top and bottom halves are not the same size. The bearings will be marked on the back with the size and when they were made..

IF THE CRANK MEASURES STANDARD.....Use standard size bearings.
Clearance at .0025" on both rods and mains works well.

You mentioned fresh water cooling
Might be a good idea to use a good antifreeze with the good protection package to protect the block, heads and water pump from corrosion.
I have had experience with boats but they were drag boats and we cooled them directly off whatever we were racing in.... We never ran in salt water though.

Looks like a trip to the shop to get the block dipped in the hot tank or parts washer and get the thing magnafluxed is in order.

Fresh cam bearings would be in order

Another area to get a good eye on is the block deck.....Take a good look at the areas that the stainless steel fire ring seals against the block.....especially on the end cylinders close to the coolant passages.
Theses areas can see erosion of the cast iron due to electrolysis...
If the seal ring area is "Etched" into the block deck this is not good.

A slight darkening of the metal is not an issue as long as there is not a groove worn into the deck.

Decking the block can be done...Felpro offers a .010" thicker gasket to allow for this machining.

I think we have covered things fairly well.

Maybe Maverick will add something the we have not covered..

Back to the cylinders.....You mentioned rust......Were the rust spots just on the surface ????
Some small spots that are below the cylinder wall surface will over time fill in with carbon.

The measurements you posted do not look bad....

Was this engine in the boats or.....Where did it come from ??? Is there a story that goes with the engine ?????
Any idea as to when the engine was made ???

Stamped steel rocker arms or cast parts ??? Early 6.2 had cast rockers

If the engine has stamped steel rockers.....Replace the plastic thrust buttons....

The pushrods can only go in one way


These are marked in a few different ways.
Some have a paint stripe indicating the top or rocker end.
Some have a copper colored ball end that goes towards the rockers.

Issue being that only the rocker end ball is hardened....Installing these wrong will see the ball end at the rocker fail over time.......

Might want to get some pictures of the push rod ends and such posted so we can maybe see what you have.

Just an FYI
The rear cylinder measurements are larger.....The back two holes tend to run hotter .....So they get a tiny bit more clearance....

In truck the extra heat can be an issue.... In a boat with plenty of cool water....No worries