Call that Bore Scoring?
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- 356 Fan
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Call that Bore Scoring?
Call that Bore Scoring? This is Bore Scoring on a 356B S90 with NPR pistons and a broken Gudgeon Pin at 70 mph.
I am sceptical of using anything not original in my 356C, I am looking for reliability rather than outright power.
I am sceptical of using anything not original in my 356C, I am looking for reliability rather than outright power.
Robin Walker
1962 356B S90 Coupe. sold.
1964 356C Coupe RHD
1973 911S Coupe LHD
1983 924 coupe RHD
1962 356B S90 Coupe. sold.
1964 356C Coupe RHD
1973 911S Coupe LHD
1983 924 coupe RHD
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- 356 Fan
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Re: Call that Bore Scoring?
It looks like that engine was assembled without one of the wrist pin circlips. It ran for a very long time to create the groove in the cylinder wall before the pin broke.
- Don Gale
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Re: Call that Bore Scoring?
What does the piston, head, and rod look like? I'm assuming you'll open the case.
1958 356A 1600 Super Sunroof Coupe
former 1966 Euro 912 Sunroof
former 1978 Intermeccanica Speedster w/'68 912
Member Since 1983, #4039
"Nostalgia isn't what it used to be"
former 1966 Euro 912 Sunroof
former 1978 Intermeccanica Speedster w/'68 912
Member Since 1983, #4039
"Nostalgia isn't what it used to be"
- Ron LaDow
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Re: Call that Bore Scoring?
It's amazing your wrench didn't mention a dead cylinder during a tune-up; no way you could tune a carb to that cylinder and the plug had to be dripping oil
Ron LaDow
www.precisionmatters.biz
www.precisionmatters.biz
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Re: Call that Bore Scoring?
+1Chuck Allard wrote: ↑Mon Jun 15, 2020 4:36 pm It looks like that engine was assembled without one of the wrist pin circlips. It ran for a very long time to create the groove in the cylinder wall before the pin broke.
Mike
- John Brooks
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Re: Call that Bore Scoring?
I would think that would have made a different and distinct noise. I had a Circlip brake a couple years ago, but the smoke and oil consumption gave it away.
I don't think that will polish out.
I don't think that will polish out.
John Brooks
62 Roadster
66 912
84 Cab
getting pushed around in porsches since 1965
62 Roadster
66 912
84 Cab
getting pushed around in porsches since 1965
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- 356 Fan
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- Ron LaDow
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- Don Gale
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Re: Call that Bore Scoring?
Could the small end of the rod, if bent sideways and is not parallel to the crank, induce enough thrust load on the wrist pin to push the circlip out of the groove and continue to drive the wrist pin into the cylinder wall?
1958 356A 1600 Super Sunroof Coupe
former 1966 Euro 912 Sunroof
former 1978 Intermeccanica Speedster w/'68 912
Member Since 1983, #4039
"Nostalgia isn't what it used to be"
former 1966 Euro 912 Sunroof
former 1978 Intermeccanica Speedster w/'68 912
Member Since 1983, #4039
"Nostalgia isn't what it used to be"
- Martin Benade
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Re: Call that Bore Scoring?
My guess is that the pin broke first (unless the circlip was omitted) but stayed in place for the engine to run for a while, maybe even without any strange noises. I wouldn't say it was noisless but I once drove several miles back home with a broken crankshaft.
Cleveland Ohio
62 Cabriolet
56 VW
02 IS 300
04 Sienna
62 Cabriolet
56 VW
02 IS 300
04 Sienna
- Harlan Halsey
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Re: Call that Bore Scoring?
In the 1960s I lent a VW with a freshly rebuilt 40 horse to a friend to drive from Boston to Maine and back. I must have left one of the wristpin circlips out. The car began to smoke on the return, and was using a quart/50 miles at the end. I think my friend just went to the nearest gas station and put a couple of quarts in when the red light came on. One pf the cylinder walls looked just like the picture above. Only the cylinder was damaged. I replaced the piston and cylinder, and all was well from then on. An embarasing mistake. But if you re wondering how long it takes to do that, it took about 300 miles to go deeper than 1/8".
- Ron LaDow
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Re: Call that Bore Scoring?
616 rods are 'bottom-guided' and the top end is centered in the piston, so there should be no asymmetric load to bend the rod. Regardless of theory, I also had an NPR PC set kick a circlip out and score a cylinder in a similar manner many years ago.
I cannot tell you the cause, but since then I am careful to examine the circlips on installation and make sure the 'sharp' surface (take a look; you'll see it) is on the 'outside' engaging the groove cut in the piston.
Similarly, the results are not proven causative, but I've never had a similar failure since then.
Ron LaDow
www.precisionmatters.biz
www.precisionmatters.biz
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Re: Call that Bore Scoring?
+1,Ron LaDow wrote: ↑Sat Jun 27, 2020 1:08 am616 rods are 'bottom-guided' and the top end is centered in the piston, so there should be no asymmetric load to bend the rod. Regardless of theory, I also had an NPR PC set kick a circlip out and score a cylinder in a similar manner many years ago.
I cannot tell you the cause, but since then I am careful to examine the circlips on installation and make sure the 'sharp' surface (take a look; you'll see it) is on the 'outside' engaging the groove cut in the piston.
Similarly, the results are not proven causative, but I've never had a similar failure since then.
The sheared sharp edge, of which Ron wrote, is called out, and the installation index he described, is included in one of the aircraft engine publications I sourced in my FAA aircraft engine work over the years. It is important...!
Thanks, Ron,
Mike
- Martin Benade
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Re: Call that Bore Scoring?
So it’s not just a good idea, it’s standard aircraft practice?
Cleveland Ohio
62 Cabriolet
56 VW
02 IS 300
04 Sienna
62 Cabriolet
56 VW
02 IS 300
04 Sienna
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- 356 Fan
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Re: Call that Bore Scoring?
Martin, it was in my shop, and I never had a failure using that process. I also still have the rod alignment tool with which I checked the rods for trueness. Older machind shops may have one. I never found a bent rod in those engines, but by comparison, they were massive. I did, however find a couple which were flawed, in the magnaflux process, one of an NOS set for a Ford 427 engine, which an old Friend was going to use in a stroked 428, out to 454, in a '67 Mercury at Bonneville. He later blew it up, in a jet boat...Martin Benade wrote: ↑Sat Jun 27, 2020 2:51 pm So it’s not just a good idea, it’s standard aircraft practice?
Mike