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914World.com _ 914World Garage _ Rough cylinder walls
Posted by: Hans Jan Oct 19 2016, 09:28 PM
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.
Posted by: wndsrfr Oct 20 2016, 05:31 AM
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.
Hmm...those look like stains from the wrist pin side of the piston....metal looks ok, can see honing scratches across the stain.
Posted by: N_Jay Oct 20 2016, 07:44 AM
Are the marks on the front and back or top and bottom?
Can you feel them at all?
Posted by: injunmort Oct 20 2016, 12:43 PM
looks like some one forgot the wrist pin keepers. i have seen that before. it does not end well.
Posted by: McMark Oct 20 2016, 12:59 PM
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.
Posted by: worn Oct 20 2016, 01:12 PM
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.
Posted by: injunmort Oct 20 2016, 04:16 PM
piston speed changes dramatically at tdc and btdc. it goes from max velocity to stop.
Posted by: porschetub Oct 21 2016, 01:37 AM
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.
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 ???
Posted by: Hans Jan Oct 21 2016, 06:29 AM
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?
Posted by: 76-914 Oct 21 2016, 07:35 AM
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
Posted by: worn Oct 21 2016, 08:16 AM
piston speed changes dramatically at tdc and btdc. it goes from max velocity to stop.
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
Posted by: McMark Oct 21 2016, 08:42 AM
Yeah, I wrote that poorly. What I had in mind is that this engine may have stock rods with an increased stroke.
Posted by: injunmort Oct 21 2016, 11:59 AM
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.
Posted by: Hans Jan Oct 22 2016, 10:46 AM
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.
Posted by: cwpeden Oct 22 2016, 11:16 AM
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.
Posted by: cwpeden Oct 22 2016, 11:18 AM
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.
Highly unlikely as they are 90 degrees to the wrist pins
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