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Top end rebuild - rod bolts and Plastigage

I am doing my first ever top end rebuild, on a 993 engine. Parts are at the machinist and hopefuly will arrive soon.
I was researching on the engine assembly and there is one thing I am not clear how to do: measure the rod bearing clearance.

On another post of mine people recommended to use Plastigage. I read all posts I could find and also Wayne's book, but everybody explains how to do it with the crank out of the case.
Can somebody guide me on how to do it with the cranck installed in the case?


Is the another alternative. Like using a bore gauge? I would also need some guidance for this.

Thanks in advance

Mario
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'07 997 GT3
Old 05-04-2012, 04:35 PM
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I'm doing a complete rebuild on mine, so rods were off of the crank, everything out of the engine. I installed the new shells, then used a bore gauge to take an ID measurement. I had already used a digital mic to measure the cranks rod journals, so some simple maths gave me the clearances.

Have to say, I did also try doing a Plastigauge check on the bench, but simply couldn't hold the rods still enough whilst using a stretch gauge to tighten the rod bolts - ended up with smudged Plastigauge every time, so at that point, went only with the bore gauge measurements (which were all good anyway).

When you say that you're doing a top end rebuild, why are you looking to remove rods without splitting the case? General curiosity or do you think you have a problem?

ETA: Not sure I'd feel comfortable doing any Plastigauge checking inside a built engine; to clean it off, you need to scrape off the squished plastic - it's like candle wax sort of consistency, then you clean the residue using brake cleaner. There's significant opportunity for this old plastic to drop into the crankcase.

If you really want to check this kind of stuff, then if it were me (and it was 6mths ago) I'd be opening the bottom end as well, giving everything a thorough cleaning and also inspecting the cranks main journals and replacing the shells.
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Last edited by Spenny_b; 05-04-2012 at 06:29 PM..
Old 05-04-2012, 06:22 PM
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Spenny_b

I removed the rods in order to replece the rod bolts. Those have been highlighted as a source of failure on 993 engines.

How do knowleagable people deal with rod clearance measurement when doing only a top end rebuild?
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'07 997 GT3
Old 05-04-2012, 06:38 PM
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Quote:
Originally Posted by Spenny_b View Post
I'm doing a complete rebuild on mine, so rods were off of the crank, everything out of the engine. I installed the new shells, then used a bore gauge to take an ID measurement. I had already used a digital mic to measure the cranks rod journals, so some simple maths gave me the clearances.

Have to say, I did also try doing a Plastigauge check on the bench, but simply couldn't hold the rods still enough whilst using a stretch gauge to tighten the rod bolts - ended up with smudged Plastigauge every time, so at that point, went only with the bore gauge measurements (which were all good anyway).

When you say that you're doing a top end rebuild, why are you looking to remove rods without splitting the case? General curiosity or do you think you have a problem?

ETA: Not sure I'd feel comfortable doing any Plastigauge checking inside a built engine; to clean it off, you need to scrape off the squished plastic - it's like candle wax sort of consistency, then you clean the residue using brake cleaner. There's significant opportunity for this old plastic to drop into the crankcase.

If you really want to check this kind of stuff, then if it were me (and it was 6mths ago) I'd be opening the bottom end as well, giving everything a thorough cleaning and also inspecting the cranks main journals and replacing the shells.
Plastigauge actually dissolves quite well in oil. Mineral spirits is much better than brake cleaner for cleaning off the residue.
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Old 05-04-2012, 06:58 PM
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Bore gage is more accurate than plastigage.

Jafromobile has a very informative set of videos. This one is specifically on how to bore gage mains:
Blueprint 105 - Main Bearing Oil Clearances - YouTube

This one is from Fowler, how to use their bore gage. Notice that the set does not come with the calibration ring. Those are sold separate.
http://www.youtube.com/watch?v=ez--JYSnrsM&feature=results_main&playnext=1&list=PLF664CD0B12CD8E69
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Last edited by AlfonsoR; 05-04-2012 at 07:28 PM..
Old 05-04-2012, 07:26 PM
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Thanks Alfonso, but i keep having the same problem. The video explains how to do it with the crank out.

Anybody can explain how to measure the clearance with the crank in the case?

Thanks
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Old 05-05-2012, 06:26 AM
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If you really need to measure the crank, complete the tear-down and split the case. You're mostly there already; another twenty minutes and the cases are split. Now you can check the rods and mains and re-seal the cases correctly. There is a probable chance the intermediate shaft bearing is toast anyway...
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Old 05-07-2012, 06:28 AM
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Quote:
Originally Posted by lindy 911 View Post
If you really need to measure the crank, complete the tear-down and split the case. You're mostly there already; another twenty minutes and the cases are split. Now you can check the rods and mains and re-seal the cases correctly. There is a probable chance the intermediate shaft bearing is toast anyway...
Thats really excellent advice.

I would never use Plastigage to measure something so critical to engine durability. Use the proper micrometers to do this right.
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Old 05-07-2012, 09:24 AM
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I would split the case at this point. You have everything else removed, so good time to eyeball the other bearings and it is little extra work.
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Old 05-07-2012, 04:20 PM
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OK...you talked me into it!! The case will be splitted!!! let's pray!!

What are the things I should look for once it's open other that bearings?

I would like to keep the while in there stuff to a minimum, but do all what's necessary.

Please, advise.

Thanks
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Old 05-08-2012, 10:53 AM
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can the case thru bolts be re-used? Other than orings and seals..and bearings (I guess), what else needs to be replaced?

Thanks
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Old 05-08-2012, 11:21 AM
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Yes, you can re-use the through bolts with new green viton o-rings. You'll be looking at the intermediate shaft bearing and oil pump o-rings and about $100 for a sealant kit from Henry at Supertec. Your mains should be fine but need to be looked at while it's apart. There are many very helpful threads here to guide you. Ask lots of questions on this forum and take your time. Enjoy it; I did.

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Old 05-08-2012, 01:56 PM
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Thanks lindy911.

Actually, I already have the sealants. I would only need the seals.
One question on the seal: everybody talks about the "green viton o-rings'. Are these the ones on this kit? Pelican parts LINK

Thanks
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Old 05-08-2012, 03:14 PM
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I called our host but the sales rep was not able to confirm if the Reinz case seal kit has the green viton o-rings. Can anyone confirm if this is the case, or what brand ( and where) should I buy?

Thanks
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Last edited by mmasse; 05-09-2012 at 08:29 PM..
Old 05-09-2012, 08:24 PM
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VR set on the left from our host showing blue O-rings and a Wrightwood set on the right showing green.


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Old 05-09-2012, 11:00 PM
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Quote:
Originally Posted by mmasse View Post
Thanks lindy911.

Actually, I already have the sealants. I would only need the seals.
One question on the seal: everybody talks about the "green viton o-rings'. Are these the ones on this kit? Pelican parts LINK

Thanks
What sealants are you planning to use? There is a great thread about that very subject. Pay close attention to the wisdom of Henry Schmidt regarding this subject. I didn't know about the thread during my rebuild and didn't follow the advise given; my engine leaked at a through bolt (used blue o-rings) and at the #8 nose bearing.

Do you have Wayne's book? It's very helpful in planning the project although there are a few details that need to be updated. The most glaring is the sealant choices in my opinion. Good luck!
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Old 05-10-2012, 07:04 AM
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COnsidering that O-rings are meant mainly for joints where some movement is expected I would go with the silicon grease sealant. While Wayne certainly has done a lot of work on these engines and in his book this is a part I do not agree with. Putting RTV on the orings can restrict their inherent quality of sealing under motion as the case moves during warm up and thus cause a leak. The recommendations of Bruce Anderson and Henry Schmidt are spot on IMHO that a good silicon grease is best.

Incidently, some of the paper gaskets can be sealed with form-a-gasket aviation sealant, which is non-hardening, should they decide to leak. It has served me well for many years where rtv has let me down.
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Old 05-10-2012, 11:07 PM
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Do Henry some business and get the gasket kits from him, if indeed you can't get the greenie o-rings from Pelican.

I think you're going to find out that the most work you'll do on the bottom end is cleaning. Clean, clean, clean is a must once you crack it open. Because it takes a lot of work to clean it up so it'll go back together w/out leaking.
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Old 05-11-2012, 10:14 AM
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Lindy

I have reused the oil pump O rings over and over and over. You can see where they bulge a little in the middle, but never a problem. These are well captured. I have yet to see one with signs of distress, cracks, or brittleness. Same with the engine oil cooler rings, and the seal to the oil inlet.

Have you had a different experience?

Of course, if a guy springs for a complete kit, no particular reason not to use all of its new parts. Been a long time since I bought a kit, though. A while back I bought a bag full of the through bolt O rings. About the only seal/ring/gasket that simply can't be reused because some part of each one is always a bit torn. Alas, I now find out, the blue kind. Though they haven't leaked on me.
Old 05-11-2012, 10:03 PM
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Lindy

I have reused the oil pump O rings over and over and over. You can see where they bulge a little in the middle, but never a problem. These are well captured. I have yet to see one with signs of distress, cracks, or brittleness. Same with the engine oil cooler rings, and the seal to the oil inlet.

Have you had a different experience?

Of course, if a guy springs for a complete kit, no particular reason not to use all of its new parts. Been a long time since I bought a kit, though. A while back I bought a bag full of the through bolt O rings. About the only seal/ring/gasket that simply can't be reused because some part of each one is always a bit torn. Alas, I now find out, the blue kind. Though they haven't leaked on me.
Walt,

I'm sure you're right about the re-use of the oil pump o-rings. It's simply a matter of not trusting myself to make the judgment call of whether or not they are still usable. Since they are relatively cheap (in the Porsche world) it's an easy call (on of the few) for me.

I'm now of the opinion that there is more to the through bolt leaks than the o-ring. It appears that some of the SC cases were without the chamfer on the through bolt hole, usually the drivers side, and can cause some problems with the o-ring no matter what the make or type (blue or green). I had blue ones leak and replaced them all with green Viton and they leak too. The o-ring gets pushed out and pinched by the washer and doesn't seal.
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