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And the rebuilt engine is being mated back to the trans today.
I've had a few other posts getting info, and many others chimed in with Qs, including a few PMs and such. I thought I would share my decision process and what led to what, where I drew lines, etc.
Background: Dual use street/track, 1995 Porsche 911. Mods in the sig line, but already have short ratio gears and LSD added in. I also already have the LWFW.
Bought about 5 years ago at 46k miles. Now 74k mi. Due to injuries, flat tires, poorly timed mechanical issues, and family time, in those 5 years probably less than 30 track days.
The problem:
It was idling rough. Seemed a little low on power in the upper bands. Had a little blip at about 2800 RPM consistently. So I took it in. Quick compression test showed it at about 30% of the compression it should have in one of the cylinders. Leakdown confirmed that cylinder had issues on I think exhaust, and others had smaller leaks. I don't recall on intake or exhaust.
Time for a second opinion, just to be sure. Confirmed.
The research:
So now I have a quandary. Of course they need to get in there to see what's up. But what should my game plan be? Just a top end? Include bottom end? Springs? Rods? 9m? Go insane? Just put back to stock? 3.8? Slip in or bore out? Cams? It gets dizzying fast.
So I did a bunch of research here, but the best advice I can give is what I did. I bought an hour with Steve W twice. Once so I could decide what to do BEFORE I was in there and massively confused, and once again when I knew the details. It was invaluable.
Options:
- Just put it back to stock. Keep everything, upgrade the valve guides, top end maybe, but keep as is.
- Do a bit: Cams, valve guides, be happy.
- 3.8 (sane level): means doing RS cams
- 3.8 insane level: could do anything, but also need rods and such
- 9m: Seems great but hard to do this side of the states
So, after a lot of research, I decided that I would not spend the money on a 3.8. I would get some Web Cams RS cams, tweaked by Steve Weiner for improved street-level idle. Save the money for something else someday, or maybe a 997 GTS someday.
The 3.8 is really just like 143cc or something like that in terms of added displacement. It is a lot of money if you are pulling a healthy engine to do it, and for the less than 10% HP bump, a lot of $/HP. The cams were only about 1500, make it a little zoomier, and seemed a good compromise.
Going beyond that you sort of make a big step up to $35k+, messing with rev limits, Motec, all sorts of stuff. It can be done, but it ain't cheap.
The reality:
So this happened:
Cracked intake valve, almost to the center, REALLY lucky it didn't fall out and grenade the whole thing at the track, or worse yet, with my family in the car.
Tear it down more. Some (not sure how many) cylinders out of round, mechanic worried about bottom end wear and damage as top end was pretty oily.
Assessment from mechanic: Not an over rev, valve guides seem particularly bad, heat and leakdown from valve guides would not have been bad enough to cause crack on the intake valve. Mostly likely a bummer combination of particularly out of spec valve guides from the factory, plus a valve that just wasn't so strong, perhaps a metallurgical flaw.
I know that will spark debate and everyone is entitled to their opinion, but a very experienced and very reputable and very race oriented local shop said just bum luck, most likely.
The solution:
So now keeping it stock is going to be a lot more money than I'd hoped. So the incremental of 3.8 vs. 3.6 wasn't much, and I was planning on doing the cams anyway, so I decided 3.8. I agonized over slip in vs. bore in, and decided that since I wasn't increasing revs and going bigger than 3.8, yada yada, I would go with slip in.
I also decided not to do rods for the same reason. Not raising the revs, and not going bigger than 3.8, and they were inspected to be in great shape.
The shop wasn't comfy in not getting into the lower end given the oily mess up top. I wish I could have them do more forensics and really decide if it was all necessary, but ok. So new rod bearings and crank bearings, etc. Torn down.
Since new springs were another $800, and I wasn't raising the revs, I kept the springs. I did have to replace some of the lifters and a few of the rocker arms (could have potentially resurfaced instead), and all intake and exhaust valves. Also upgraded valve guides, rebuilt the heads, new timing chains, and a few bits and bobs. Did main bearing, rod bearing, intermediate shaft bearings, gaskets, etc.
So, it's supposed to be mated today/tomorrow, and fired up.
I'm debating which chip I want to use, and debating whether to go through expense and hassle of dyno file (Can't do live dyno tune on 95, apparently).
That's my logic. Hope it helps someone going forward. Took me a long time to get here.
And the rebuilt engine is being mated back to the trans today.
I've had a few other posts getting info, and many others chimed in with Qs, including a few PMs and such. I thought I would share my decision process and what led to what, where I drew lines, etc.
Background: Dual use street/track, 1995 Porsche 911. Mods in the sig line, but already have short ratio gears and LSD added in. I also already have the LWFW.
Bought about 5 years ago at 46k miles. Due to injuries, flat tires, poorly timed mechanical issues, and family time, in those 5 years probably less than 30 track days.
The problem:
It was idling rough. Seemed a little low on power in the upper bands. Had a little blip at about 2800 RPM consistently. So I took it in. Quick compression test showed it at about 30% of the compression it should have in one of the cylinders. Leakdown confirmed that cylinder had issues on I think exhaust, and others had smaller leaks. I don't recall on intake or exhaust.
Time for a second opinion, just to be sure. Confirmed.
The research:
So now I have a quandary. Of course they need to get in there to see what's up. But what should my game plan be? Just a top end? Include bottom end? Springs? Rods? 9m? Go insane? Just put back to stock? 3.8? Slip in or bore out? Cams? It gets dizzying fast.
Options:
- Just put it back to stock. Keep everything, upgrade the valve guides, top end maybe, but keep as is.
- Do a bit: Cams, valve guides, be happy.
- 3.8 (sane level): means doing RS cams
- 3.8 insane level: could do anything, but also need rods and such
- 9m: Seems great but hard to do this side of the states
So, after a lot of research, I decided that I would not spend the money on a 3.8. I would get some Web Cams RS cams, tweaked by Steve Weiner for improved street-level idle. Save the money for something else someday, or maybe a 997 GTS someday.
The 3.8 is really just like 143cc or something like that in terms of added displacement. It is a lot of money if you are pulling a healthy engine to do it, and for the less than 10% HP bump, a lot of $/HP. The cams were only about 1500, make it a little zoomier, and seemed a good compromise.
Going beyond that you sort of make a big step up to $35k+, messing with rev limits, Motec, all sorts of stuff. It can be done, but it ain't cheap.
The reality:
So this happened:
Cracked intake valve, almost to the center, REALLY lucky it didn't fall out and grenade the whole thing at the track, or worse yet, with my family in the car.
Tear it down more. Some (not sure how many) cylinders out of round, mechanic worried about bottom end wear and damage as top end was pretty oily.
Assessment from mechanic: Not an over rev, valve guides seem particularly bad, heat and leakdown from valve guides would not have been bad enough to cause crack on the intake valve. Mostly likely a bummer combination of particularly out of spec valve guides from the factory, plus a valve that just wasn't so strong, perhaps a metallurgical flaw.
I know that will spark debate and everyone is entitled to their opinion, but a very experienced and very reputable and very race oriented local shop said just bum luck, most likely.
The solution:
So now keeping it stock is going to be a lot more money than I'd hoped. So the incremental of 3.8 vs. 3.6 wasn't much, and I was planning on doing the cams anyway, so I decided 3.8. I agonized over slip in vs. bore in, and decided that since I wasn't increasing revs and going bigger than 3.8, yada yada, I would go with slip in.
I also decided not to do rods for the same reason. Not raising the revs, and not going bigger than 3.8, and they were inspected to be in great shape.
The shop wasn't comfy in not getting into the lower end given the oily mess up top. I wish I could have them do more forensics and really decide if it was all necessary, but ok. So new rod bearings and crank bearings, etc. Torn down.
Since new springs were another $800, and I wasn't raising the revs, I kept the springs. I did have to replace some of the lifters and a few of the rocker arms (could have potentially resurfaced instead), and all intake and exhaust valves. Also upgraded valve guides, rebuilt the heads, new timing chains, and a few bits and bobs. Did main bearing, rod bearing, intermediate shaft bearings, gaskets, etc.
So, it's supposed to be mated today/tomorrow, and fired up.
I'm debating which chip I want to use, and debating whether to go through expense and hassle of dyno file (Can't do live dyno tune on 95, apparently).
That's my logic. Hope it helps someone going forward. Took me a long time to get here.
Steve Wong has the chips for your engine. Off the shelf it's good, but you can opt for a custom. To get a custom you buy a chip, dyno, send the data to him and he will burn another. repeat if necessary.
Steve Wong has the chips for your engine. Off the shelf it's good, but you can opt for a custom. To get a custom you buy a chip, dyno, send the data to him and he will burn another. repeat if necessary.
Thanks. That's what I'm thinking too. Or Steve Weiner.
Hey guys, my shade tree car works ends with internal engine repair.
I'm not an engine technical guy and I am asking this question just to understand what scope of work is minimally needed to address the compression loss.
What would be the issue with just checking the seat on the one cracked valve and grinding or replacing the seat if needed and replacing the one valve?
Hey guys, my shade tree car works ends with internal engine repair.
I'm not an engine technical guy and I am asking this question just to understand what scope of work is minimally needed to address the compression loss.
What would be the issue with just checking the seat on the one cracked valve and grinding or replacing the seat if needed and replacing the one valve?
Other's thoughts?
Andy
So........ when one fence slat is rotted and failing, your intent is to fix just one?
Hey guys, my shade tree car works ends with internal engine repair.
I'm not an engine technical guy and I am asking this question just to understand what scope of work is minimally needed to address the compression loss.
What would be the issue with just checking the seat on the one cracked valve and grinding or replacing the seat if needed and replacing the one valve?
Other's thoughts?
Andy
So the engine is out and torn apart just to do the ONE valve that's clearly damaged. All other known issues (worn valve guides, leaking seals, etc.) will be ignored since there are no other "obvious" issues.
One that wants to go this route better be tough...
What would be the issue with just checking the seat on the one cracked valve and grinding or replacing the seat if needed and replacing the one valve?
If the rest of the engine was healthy, nothing would be wrong with fixing just a cracked valve. But this engine was burning massive amounts of oil because all the guides and valve stems were worn. When you tear down an engine that is worn in many different ways, you address everything while it's apart.
As we discussed previously, no, it was not burning massive amounts of oil. That said, to answer the question, one problem often begets others. And the valve guides are a known issue. I had a smaller leak on other cylinders due to this so it made sense to do more. And as Churchill pointed out, lots of "while you are in there" parts.
It's $2k just to get the engine in and out. Once out you do everything you can.
11-09-2017, 01:08 AM
It started with a rough idle...
