How-to drill oil drain holes in 3.5L pistons

[MSHardeman]

Here are the instructions that I got from Jerry Lemond on how to drill extra oil drain holes in our 3.5L pistons:



Drill a hole, the same size as the ring land, where the two black lines are on the skirt, right under the two factory drilled oil holes, then drill holes to the left and to the right at the other black lines right besides the boss where the wrist pin is. Use a battery powered hand drill set to slow speed with a new sharp drill bit. It drills very easy.

EDIT: To be clear, and I double checked with Jerry, the holes need to be drilled IN the ring land and not on the skirt of the piston.
Simple and to the point.

[blacksambo]

Very nice. Thanks

[89Vette]

And, here is the reason for the iffy longevity that some posters have reported. There's been arguments/debates over what the issue really is. But, I posted on this after talking to Jerry in 2010.

Those tiny holes you see are where the oil has to drain back into the pan. If they get clogged, oil pools in the cylinders and starts creating the havoc -- that eventually leads to engine failure.

It's why I would be cautious about doing anything like: using engine cleaners, running heavier than recommended oil, skipping an oil change, or adding things like teflon treatments to your crankcase.

I believe these holes are either fewer or smaller than idle (compared to other engines). It doesn't mean the engine can't work or last a long time -- just that dilegence to recommended maintenance is the key to success.

I would think doing anything like this would benefit by balancing/rebalancing the rotating assembly -- though doing it equally to all cylinders SHOULD minimize the impact.

The fact that this mod is even mentioned is the biggest tell-tale to me -- but it's nice to see this posted as a way to improve any rebuild effort.

Thanks for posting!

[VX KAT]

And, here is the reason for the iffy longevity that some posters have reported. There's been arguments/debates over what the issue really is. But, I posted on this after talking to Jerry in 2010.

Those tiny holes you see are where the oil has to drain back into the pan. If they get clogged, oil pools in the cylinders and starts creating the havoc -- that eventually leads to engine failure.

It's why I would be cautious about doing anything like: using engine cleaners, running heavier than recommended oil, skipping an oil change, or adding things like teflon treatments to your crankcase.

I believe these holes are either fewer or smaller than idle (compared to other engines). It doesn't mean the engine can't work or last a long time -- just that dilegence to recommended maintenance is the key to success.

I would think doing anything like this would benefit by balancing/rebalancing the rotating assembly -- though doing it equally to all cylinders SHOULD minimize the impact.

The fact that this mod is even mentioned is the biggest tell-tale to me -- but it's nice to see this posted as a way to improve any rebuild effort.

Thanks for posting!

can you edjamacate me...I'm not understanding the correlation between using engine cleaners or teflon treatments and the potential for clogged holes on the piston??

and what rotating assembly? how would more holes affect balancing the "rotating assembly"?

sorry Mark...didn't mean to TJ your thread....

[Scott Larson]

Engine cleaners can dislodge sludge and deposits in the oil galleys and crankcase sending them through the engine to be redeposited elsewhere, like in the pistons drainback holes. As to balancing, I would be more concerned with the reciprocating part of the equation but not much due to the fact that you are drilling the same size and amount of holes in each piston and the fact that they are so small as to be of negligable effect on the rotating assembly. We're not talking 10,000 rpm race motors here...

[SilverBullet75]

Sue,
Rotating Assembly= Crankshaft, connecting rods, pistons, piston pins, and possibly the camshaft.
Basically all the rotating internal parts of the engine that produce power output.

Also, balancing an engine involves removing metal on internal parts to compensate for heavier sides of that part.
It's similar to balancing tires. The shop will add weights to compensate.

In the case of the piston holes, I think the concern is that you have just removed metal, though minute amounts, but it could easily be enough to cause a disturbance in the Force...

[Scott Larson]

Oh, and Sue, the rotating assembly is the crankshaft and the reciprocating assembly is the sum of the pistons, rings, connecting rods, rod caps, rod bolts, wrist pins and pin retainers (everything that's moving up and down with the pistons).

[VX KAT]

oh, I get it now..thanks guys! ironic that cleaners can cause both clogs and leaks....

[89Vette]

Engine cleaners can dislodge sludge and deposits in the oil galleys and crankcase sending them through the engine to be redeposited elsewhere, like in the pistons drainback holes. As to balancing, I would be more concerned with the reciprocating part of the equation but not much due to the fact that you are drilling the same size and amount of holes in each piston and the fact that they are so small as to be of negligable effect on the rotating assembly. We're not talking 10,000 rpm race motors here...

First of all, I had a typo (or brain fart). The following sentence should have read...
I believe these holes are either fewer or smaller than ideal....

I don't know enough about this small weight change in engine balancing -- but if I were going to do it (with an engine rebuild), I'd do it before the rotating assembly were balanced -- just to be sure.

Sue,
There are giant "lobes" on a crankshaft. They are counterwieghts to the pistons. Without those counterweights, the forces generated at higher rpms would shake the motor apart. (Note: a giant weight on the end of the crankshaft -- called the harmonic balancer also performs some of these duties.)

What most people don't know is there are variances in piston weights. There can be small variance from one (like kind) piston to the next. Or, pistons weight can change due to the material used in casting/forging the pistons. For example, standard weight Chevy pistons were approx 600 grams. With my rebuilt 383 performance motor, they weight about 400 grams. Because different makes and weights of pistons can vary alot in weight (even 50% differences), the crankshaft must be individually counterbalanced to match those weights. This means those crankshaft counterweights need to be adjusted. (To do this, a machinist spins the crank along with weights (I believe equivalent to the pistons/rods being used. IOW, I'm not sure they use the actual piston.) Either way, just like a tire balancer, the machine tells you how much weight change is necessary to balance the counterweights to offset the weights of the rods and pistons.

Here is the rotating assembly in a typical engine....


Because I used very light pistons in my Corvette rebuild, the builder decided to drill out (remove) weight from my crankshaft. Here's my Corvette crankshaft after balancing. Notice the holes in the lobe. It didn't look that way before balancing.


Any compared to tiny extra holes in the pistons, you would assume it might not affect the outcome of balancing. OTOH, you'd probably be surprised at the force a piston generates when moving up/down at even 5-6k rpms. Also, know that a VX crankshaft balancing principle is the same -- though it only has 6 rods/pistons vs the eight in a V8 engine.

Note: For factory balancing, automakers demand a weight tolerance (from manufacturers) so they can weight every crankshaft the same -- and assume it will match the pistons going in a given engine. Factories don't match balance every single engine. There is some "tolerance" that won't be felt by the consumer -- as mentioned above. Because of the small amount of weight being removed from each piston, they effect on balancing may be negligible (as Scott suggests). But, it wasn't the major point of my first post in this thread.

[Scott Larson]

No offense intended to anyone, but the assembly shown is the rotating and the reciprocating assembly. It is made up of the crankshaft, along with the pistons and all attaching hardware (con rods, caps, rod bolts, etc...). In performance-engine building, the weights of all components is taken into consideration and balanced to one another using the lightest of each component as the "standard" with each like-component (con rods with con rods, pistons with pistons, etc.) matched to it by grinding away excess material left in the casting process for that purpose. Typically the crank is balanced first to establish a stable baseline to work from and is accomplished by drilling holes in the counterweights as shown in the picture of Vette's 383 crank. Plug-weights are also sometimes used in the drilled-out recesses to achieve a specific weight by increasing it to correspond with the weight of the reciprocating mass. The harmonic balancer is not a weight per-se, but actually a fluid-filled damper intended to cancel out unwanted and sometimes quite destructive vibrations caused by accoustic harmonics (a cumulative effect of all engine vibrations achieving harmony to the point of catastrophic failure). I hope this didn't muddy the waters, just trying to help...

[Scott Larson]

By the way Vette, that's one sweet looking crank! Balanced, chamfered and relieved...someone does nice work!

[MSHardeman]

And, here is the reason for the iffy longevity that some posters have reported. There's been arguments/debates over what the issue really is. But, I posted on this after talking to Jerry in 2010.

Sorry y'all. I totally spaced out and didn't explain WHY you would want to drill holes in your pistons.

As 89Vette said, one of the theories as to why some of our engines burn oil is that Isuzu used some bad/iffy rings and not enough oil drain holes in the pistons when they originally built these motors. The oil drain holes in the pistons are there, as Vette said, to drain oil back into the crank case. As the rings, and oil scrapper travel down the cylinder wall they are supposed to squeegie the oil off of the cylinder wall, and either push it back down into the crank case out of the bottom of the cylinder, or force it into the drain holes. The original drain holes are thought, by some, to be too few and too small thus not draining enough oil, or getting clogged and not draining any oil at all.

The pistons in the new Isuzu motors have more, larger, drain holes and this may be why most of the new motors don't burn any oil. Jerry's instructions above provide a way to make the existing drain holes larger, and add additional drain holes to hopefully stop the oil burning issue in the older engines. Jerry has done this fix to numerous engines and he said that it works very well. He didn't mention that it might throw the balance of the engine off, but since you would be removing such a small amount of material and can't see how it would effect it that much, if at all.

Obviously (well, maybe not to some), the engine has to be completely taken apart to accomplish this fix, so it is really for those who are looking into re-building their engines, or who have the time to take their engine apart to do the fix and then put it back together.

If you get a re-built/remanufactured engine, it is not guaranteed that the shop used the new Isuzu pistons so you could be getting an engine that will have the same oil burning issues as before. Jerry said that he has ordered a few remanufactured engines to see if they were using the new pistons, or at least drilling them out, and most, if not all of them, had not.

[PK]

Thank goodness for the edit on your first post.
I was starting to think that Jerry was having a seniors moment.

PK