Cylinder liner and pistons specs

[txhokie4life]

I've got an rsr replica engine that I got with the car.

Previous owner said he pulled if off the track with piston slap issues.

I tore down the engine and noted the following with a machinist doing the measurements.

Mahle cylinder sleeves, mic out to
~102mm
Ross pistons with 5-6. 1/1000 clearance.

The cylinder liners are nikisil and show no obvious signs of wear.

The pistons show scuffing on lower skirt, some near ring landings.

This is a race only engine.

The machinist doing the measuring was concerned that the sleeves may have been 3.6 sleeves (100mm) and bored out to 102mm
(I was wondering if Mahle had 102's???)

We are wondering how thick the cylinder walls should measure?
According to him they are thin.
But he doesn't have an air-cooled back ground

Anyone have specs for 102mm Mahle?

We're wondering that maybe the cylinder is too thin and heating up and expanding too much and the clearance is growing too large allowing the piston to wobble around. Just thinking out loud....

If you can't tell, I'm not a mechanic, learning, but I don't know the lingo, so I apologize if I used the wrong terms

We think the pistons need to be replaced, but not sure on the cylinder liners.

Don't want to spend money needlessly.

This will be a de/track car
Probably never a true racer.

Thanks

Mike

Thx for help and pointers.

[Flieger]

MAHLE pistons are of a special high-silicon Aluminum alloy- 4032 which is the same as their cylinders and which expands less with temperature increase. This alloy is harder to forge than lower-silicon Aluminum alloys so many aftermarket piston manufacturers like JE use 2618. As a result of the greater expansion, the cold clearance with a 2618 piston in a 4032 bore must be greater. LN Engineering's Nickies cylinders match the expansion of JE pistons.

Do Ross use 2618 alloy? That could be the cause of the noise on start-up.

[Flieger]

There is some good discussion of the alloy properties and advantages/disadvantages in this thread: 6061-t6 cylinder head

[txhokie4life]

I do not know if the piston slap was at hot or cold. I'm going by second hand experience
of the PO and he admitedly doesn't know anything about engines.

2618-T61 per the Ross website:

All ROSS Racing Pistons (since 1985) have been forged from 2618 billet bar stock and have been heat treated and aged to a T61 condition (2618-T61). 2618-T61 is the material that is used when fatigue resistance and durability are of prime importance by all premium racing piston manufacturers. This material has less than 1% silicon particulate content. High silicon content pistons (forged from 4032 or MS75) will not stand up to the most extreme stress placed on many racing pistons. If a crack starts to form in a high silicon piston it will continue until the piston experiences a catastrophic failure. Simply stated, adding sand to the aluminum only makes it more brittle. In the rare instance of a 2618-T61 piston cracking, the crack will continue to an area where the stress is not as great and will then stop. Another advantage of 2618-T61 over the high silicon pistons is the ability to keep its shape under extreme pressure and high RPM's. "Skirt Shrinking" is not a problem with ROSS Racing Pistons.

[HawgRyder]

You might also look into Teflon buttons for the pistons.They go into the skirt at right angles to the pin.
The idea being...to hold the piston vertical in the bore...preventing piston slap.
A by-product is...very good ring wear (because piston does not "rock").
We used them in drag engines...usually 3 of 4 to a side on each piston.
They are a force fit into the piston skirt...and force fit also into the bore.
This would save you the cost of new pistons.
Bob

[txhokie4life]

Never heard of the Teflon buttons
But I'll do some research
Thank you very much!!!

[Flieger]

Originally Posted by txhokie4life

I do not know if the piston slap was at hot or cold. I'm going by second hand experience
of the PO and he admitedly doesn't know anything about engines.

2618-T61 per the Ross website:

All ROSS Racing Pistons (since 1985) have been forged from 2618 billet bar stock and have been heat treated and aged to a T61 condition (2618-T61). 2618-T61 is the material that is used when fatigue resistance and durability are of prime importance by all premium racing piston manufacturers. This material has less than 1% silicon particulate content. High silicon content pistons (forged from 4032 or MS75) will not stand up to the most extreme stress placed on many racing pistons. If a crack starts to form in a high silicon piston it will continue until the piston experiences a catastrophic failure. Simply stated, adding sand to the aluminum only makes it more brittle. In the rare instance of a 2618-T61 piston cracking, the crack will continue to an area where the stress is not as great and will then stop. Another advantage of 2618-T61 over the high silicon pistons is the ability to keep its shape under extreme pressure and high RPM's. "Skirt Shrinking" is not a problem with ROSS Racing Pistons.

There you go. They are expanding more than the cylinder so you need to run them looser cold. The trade off is that they are tougher at high temps and do not over-age so quickly as the 4032. If you need new cylinders ever, go with LN Engineering Nickies to eliminate the differential expansion rates.

[txhokie4life]

I don't get that -- why would there be piston slap if the pistons are expanding more than the cylinders... I would think this would reduce the "slop" and be more inclined not to slap
assuming I understand slop as to be when the piston is allowed to travel in a non-north-south
direction and "slaps" against the cylinder wall because there is increase tolerance that allows
the sideways movement.

Now I get two different coefiicients of expansion causing an increased clearance.
But that would be the cylinder wall expanding more (or contracting less) than the piston.

Of course I may have this all f'd up.

I'm new to air cooled -- but for all things M96 Charles and I at LN do a good bit
of business together -- so if I do need new Ps&Cs -- he's the first I'll call.

thanks,

Mike

[Flieger]

Originally Posted by txhokie4life

I don't get that -- why would there be piston slap if the pistons are expanding more than the cylinders... I would think this would reduce the "slop" and be more inclined not to slap
assuming I understand slop as to be when the piston is allowed to travel in a non-north-south
direction and "slaps" against the cylinder wall because there is increase tolerance that allows
the sideways movement.

Now I get two different coefiicients of expansion causing an increased clearance.
But that would be the cylinder wall expanding more (or contracting less) than the piston.

Of course I may have this all f'd up.

I'm new to air cooled -- but for all things M96 Charles and I at LN do a good bit
of business together -- so if I do need new Ps&Cs -- he's the first I'll call.

thanks,

Mike

The engine would seize if the pistons were sized to be the same as the bore of the cylinders when cold. The piston expands more than the cylinder as it heats so it would be bigger than the hole and seize. To counter this, the cold clearances are increased so that there is room for the piston to expand. At operating temperature the piston slap is the same as the 4032 alloy (very little). When colder than that, the piston to cylinder wall clearance is larger than it would be with the 4032 pistons.

[txhokie4life]

Ok -- I get it now -- I was of course thinking that this happened while the car was on track and
getting hot, etc.

I was further confused because the machinist mentioned he thought the cylinder walls
were too thin and implied that the cylinder liners were expanding in the heat too fast.

I've also been told about the heads:

"They will definitely need to be machined at the HG (ring) surface and that's a really specialized procedure. These have been hot enough to soften the area at the sealing ring and show some areas of distortion."

So I've been trying to piece the story together -- and I of course thought these are related issues, but then again maybe too separate issues.

Too much clearance at cold, and lean running at hot (causing the heads to be damaged)

Engine forensics is fun -- but quite the challenge.

Thanks for the help and insights

mike