3.3 liter piston and cylinder size

[millhaus]

I am rebuilding my 930 engine for my first time. I "quickly" measured the cylinders and pistons to 2 decimal spaces (digital calipers).

What I found was that my cylinders appear to be 97.04mm. The info I saw says they should be 97.000 to 97.0028. That would mean with rounding to 2 places that mine are at least 0.01mm too big. Possible? I guess.

My question is can I hone the Nikasal cylinders to a slightly larger size and find pistons to fit? Who would make pistons too fit. Or do I need to buy new cylinders and pistons?

Any suggestions would be helpful. I am trying to determine what can be salvaged and what has to be replaced.

Thanks

[EBS_Don]

I would first have someone with an accurate bore gauge take some measurements for you. If the cylinders are, indeed, too big, out of round, or have too much ovality then I would look at replating them if your pistons are in good shape. That way you can use standard rings and don't have to have an odd size piston made. If pistons are junk, custom JE's with a tad more compression are a great way to go.

[millhaus]

What is the largest diameter that 97mm cylinders can be honed too? What diamter are they still useable and when are they junk?

[tom1394racing]

The limiting factor in the 3.3 half finned cylinders is ovality and bore condition.

Measure them in at least 4 places (90 deg apart and top and bottom of stroke)with a dial bore gage and make sure that diameters are not different by more than 0.04 mm. You also need to do a light cleaning on the bores to check for scratches along the bore and Nikasil chipping near the top of the cylinder.

The limit on cylinder diameter will be set by the piston to cylinder clearance. If the cylinder is worn to the point were the the clearance exceeds 0.1 mm then a different cylinder must be used. To determine this, you'll need to measure the diameter of the piston for that cylinder and check the difference between that and the cylinder diameter.

[tom1394racing]

Here's some typical inspection data for 3.3 turbo pistons and cylinders

Pistons in the lower data, cylinders in the upper data

[millhaus]

Thanks for the chart. I have some questions:

Is the cylinder wera limit the allowed max? So since I am measuring 97.04mm I should be able to hone and reuse these cylinders?

It seems strange that the relationship between the cylinders and pistons varies so much esp. data set #3.

Is this spec data or from a typical engine?

Thanks

[tom1394racing]

To accurately measure the cylinder bore diameters requires a bore gauge. It can't be done reliably to the accuracy needed with a dial caliper.

You need to measure the cylinder bore in several places with a bore gauge. In the data I have shown, I measured each cylinder at the 4 locations I mentioned earlier. This checks for taper (top to bottom of stroke) and ovality (out of roundness). I have found that the 97mm half finned cylinders are prone to ovality and must be checked before they can be reused. It is rare that a cylinder will exceed the wear limit for diameter.

Once you have confirmed the bores measure within spec for taper and ovality, they can be very lightly honed using scotchbrite and soap to de-glaze them. This also cleans them up enough so that you can check for surface damage to the bores and Nikasil chipping. Don't hone them like you would for a Detroit Hot Rod motor.

You then need to measure the piston skirt diameter with a precision micrometer. The diameter is measured perpendicular to the pin axis. I measure twice in two different locations along the skirt for repeatability.

The max wear diameter of a given cylinder is practically limited by the allowable piston to cylinder clearance. If the difference between the piston diameter and the cylinder bore diameter is greater than 0.1mm, you need a bigger piston or a smaller cylinder to meet the rebuild spec for piston to cylinder clearance.

The data I have shown is typical for used pistons and cylinders. These are from a variety of different 3.3 turbo engines. A used set from an engine assembled at the factory usually shows less variation that this.

[millhaus]

AWESOME INFO!

Thank you that is very clear. I will check mine with a bore gage and micrometer and report my results for the forum if anyone is interested.

[millhaus]

I've decided that it is best to send this out to the machine shop to have checked.

I want to send out Pistons, cylinders, heads, crank, case (for stud removal), rods,..for inspection and reconditioning if possible.

Any suggestions on the best machine shop to handle everything?

I have heard of good things from Ollie's and JB racing. Can anyone else confirm these two shops or recommend others?

Thanks

[mppickett]

I've used Ollie's and was pleased. +1