Hello,

Today the shop had taken the engine out of the car, just to replace the very stiff valve springs. When the heads came off we noticed that there are rough areas on the cylinder walls. Not everywhere, but at least two areas per cylinder.

FYI:
Cylinders are 103.8 mm (by AA).
Pistons are also by AA.
Markings on cam: CWC
Valves Intake: 44.35 mm
Valve Exhaust: 38 mm

My question to the brain-trust is:
What could be the cause for the rough areas?

Some back ground info:
This car supposed to have "Nickies" Cylinders and JE-Pistons.
Obviously the (Craigslist) seller and I are no friends.
After receiving it, I drove the car for less then 10 minutes before the car caught on fire.


Click to view attachment

Hmm...those look like stains from the wrist pin side of the piston....metal looks ok, can see honing scratches across the stain.

Are the marks on the front and back or top and bottom?

Can you feel them at all?

looks like some one forgot the wrist pin keepers. i have seen that before. it does not end well.

I can see from the cylinder fins that those marks are on the top or bottom. I'm guessing the top since the bottom usually has oil leaking out of it.

My WAG (wild ass guess) is that it's something to do with the rings chattering or piston rock. 104 pistons aren't really reliable. Did you measure the stroke? An engine that uses 104s has to have a lot of other engine components upgraded to do right. If the rest of the components aren't right things like piston speed and rod ratio can cause problems.

Building a 104 engine right will cost as much or more than buying a 911 engine, but won't be nearly as reliable or powerful. Check over the rest of the components, but if I were you I would plan on installing new 96mm pistons and cylinders.

I cannot see piston velocity changing since that is RPM given constant rod length. It is gonna be more over square fear sure. What else needs to be done to make things work? Love to learn from you guys.

piston speed changes dramatically at tdc and btdc. it goes from max velocity to stop.

huge cylinders that go out of round when hot and out of shape,the heads get less supportive @ register size,see the hone marks still there but think not much is staying round ,AA pistons ????? some don't get good press.
I tend to remember the thin T1 no bore kits from a long way back,same issue for another reason,just saying ???

Thanks for your input.
What is is T1?

Type 1 = VW and some bus

That isn't exactly an explanation. What I was suggesting is that given the same crank and rods, how does the diameter of the piston alter piston acceleration and speed? At a given RPM, I would have expected the larger pistons to move in the same path as the smaller ones. Now they will be more over square and perhaps be less stable with a short skirt. Also, it does look like marls from the wrist pin. How does the diameter play into that?

Thanks

Yeah, I wrote that poorly. What I had in mind is that this engine may have stock rods with an increased stroke.

my apologies worn, i misunderstood the question. i dont think diameter would cause these marks, i have seen this in motorcycle engines when a wrist pin clip is not installed. when the engine gets to operating temp the wrist pin will bounce in and out of the piston contacting the cylinder wall. it will mangle the cylinder if left unattended.

Oh my GOD. That would be a disaster.
Will call the shop first thing on Monday to check.

Thanks guys.

From a machinists point of view, those look like resonance rings.
As the cylinders were machined they were ringing and that pattern can translate all through finishing.

Highly unlikely as they are 90 degrees to the wrist pins