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Quote:
Originally Posted by brighton911 View Post
Neil, many thanks for taking the time to share your wealth of knowledge. They are always an interesting read and I am richer for them.
You're welcome. I'll post something in the next couple of days regarding the Oil pump, Crankshaft, crankshaft and rods, and the closure of the case.

A lot has been written about which oil pump to use, modifications to the oil pumps etc. Some of it is relevant and some I, have some doubts about.

Old 12-27-2019, 02:39 PM
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911 Crankshaft.

This about what to look for when reconditioning a crankshaft, not any sort of modification. What to do when rebuilding your engine.

Once the rods have been removed from the crankshaft, some basic inspections should take place. How do the journals look? If they show signs of wear, any scoring from dirt, is the flywheel mating surface in good condition. Does it look like the flywheel has come lose and any metal transfer happened? The earlier 6 bolt crankshafts came loose, and the flywheel face would show signs of metal transfer. The later crankshafts went to a 9-bolt connection which has proven successful. These inspections give you an idea what repair may be required.

The threaded bores for the flywheel bolts should be checked along with the front crank pulley bolt bore. If any if these need repair, be extremely careful. Make sure you know the thread class and if the flywheel bores need repair, do not force the repair tap past the bottom of the bore as it will push the thrust face inwards where the bearing runs. This part of the crankshaft is “soft”.

The next procedures should be based on a certain sequence.

Nondestructive Magnaflux crack checking is first. If the crank is cracked it could be non-repairable, so no other checking will be needed. They can be welded if the crack is in a certain direction. Your machine shop will advise here. This can get expensive.

Next, the crank should be straight checked. All cranks will have some bending after use. Remember these cranks do twist and often bend around the 2nd main journal. Harmonics is a problem with these crankshafts. I won’t go into this here, but if interested read my paper on the PD web site.

After the crank is straightened, the galley plugs should be removed so the crank can be flushed cleaned on the inside as well as the outside. An easy way to re plug is to thread the galley drillings. This make future cleaning easier. This should be done now.

The journals could need cutting undersize, repairing back to std or polishing. If polishing is all that is required, they will now be measured to make sure they can be held at the finished size within spec, after polishing. If regrinding undersize is required, the machine shop should call you asking if you want to continue, as bearings become expensive.

Once regrinding undersize and all polishing is completed, the crankshaft needs to be balance checked. As these engines have opposed piston positions, no “bob weights’ are needed when balancing. The crank can be balance checked without any weights but should be done with the front pulley or any damper used. As any balance adjustments are done from outside in, the crank pulley or damper does make a difference. If you think you will not change the flywheel, add this now too. The whole assembly can be done together, or the flywheel can be zero balanced on its own. Done this way, the flywheel can be changed at any time without the need to re balance the crankshaft. Do not be tempted to lighten the crankshaft by knife edging. These cranks need all the counterweight they have. If you want to lighten the crank any, do so after re calculating the reciprocating weights verses the counter- weight. You must decide what percentage of counterweight you want to run. The only safe removal of any material is to slightly bull nose the counterweights. There is essentially no oil in the “sump” the counterweights spin in. All the oil left in the case not scavenged, is stacked up against the inside wall due to centrifugal force. Knife edging looks great outside the engine but inside does absolutely nothing.

Do not knife edge these crankshafts and if you will be using 6 bolt crankshafts, make sure you have the harmonics under control. My advice is, whenever possible use a 9-bolt crankshaft. If you are adding stroke, rod length and piston weight, my advice is to change over to a 9-bolt crankshaft. Engine speed and harmonics has caused 6 bolt flywheels to come loose in the past. The early RSR engine had issues with flywheels coming lose and although these engines ran slightly higher RPM’s and only made approx.325BHP, they could never keep their flywheels attached. Anyone considering a “hot rod’ version of these engines should seriously consider the 9-bolt crankshaft conversion.

Once all balancing is completed the crank requires thorough cleaning. Then the galley plugs should be re fitted and the crankshaft oiled and bagged ready for assembly. If storing the crankshaft for long periods of time, it should be hung vertically.

To conclude, all repair work needs to be done in a process, so no repair is done unnecessarily. Any repair work performed needs to be noted and if the journals need cutting undersize, make sure who ever is doing this, asks you first. Make sure they know the finish sizes after polishing. Polishing can help at times to increase bearing clearances but should only be done when you fully understand the bearings available.

If I have missed a step or you have other relevant suggestions, please go ahead and add here.

Last edited by Neil Harvey; 12-30-2019 at 11:19 AM..
Old 12-30-2019, 11:12 AM
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Hi Neil
Thanks so much for your informative posts. What size are the grub screws for the crankshaft galley ports?
Old 01-03-2020, 02:55 PM
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It appears to me that a good size is 5/16-24 threads and 1/4 length. This is the size that Marine Crankshaft installed on my 3.0L SC crank and they fit nicely. Since theyre not tapered pipe thread plugs, I would suggest thread locking compound to ensure none come loose AND it should help you resist the urge to overtighten them






And since Neil mentioned some of the things not to do, Ill ask his thoughts on cross-drilling the crank at the number 4 main journal. Doing so intersects the oil delivery galleys inside the crank for rod bearings #2 and #5.

These two rod bearings are the last to receive oil since oiling originates from the ends of the crank via #1 and #8 main bearing locations. In order for it to be most effective, the oil holes in the #4 crank main journal, #4 bearing and #4 main bearing engine case oil galley need to be enlarged. You also need to groove the bearing (or the journal itself) to ensure oil from the case enters the crank and delivers oil to the #2 and #5 rod bearing galleys as intended

Im not implying this is a must. Just speaking from experience on an engine run low on oil. Those middle rod throws on the crank are indeed the first bearings that get smoked when the crank is not receiving all the oil it needs. Not saying this is a solution for insufficient oil fill volume. Just an extra level of protection so to speak
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Old 01-03-2020, 05:24 PM
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#4

You are correct.
Old 01-03-2020, 05:54 PM
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Yes indeed groove the journal and cross drill the center main. My post was about typical work not about modifications. But really good advice.

I think Boxster main bearings come as gutter types and I think they fit. Best to check but I seem to remember these bearings will work. Saves some crank work.
Old 01-03-2020, 07:29 PM
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Never groove the journal, or drill a #%?!ing hole through your crank. It is not the solution. I think this is the only forum not dedicated to pre-war Bentley’s that still discusses it.

https://www.mahle-aftermarket.com/media/local-media-north-america/pdfs-&-thumbnails/support_technical_bulletins_pdfs/tb2051.pdf

On a more pleasant note, behold the incredible hollow crankshaft!

http://www.f1-forecast.com/pdf/F1-Files/Honda/F1-SP2_08e.pdf
Old 01-04-2020, 11:57 AM
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"To each his own".

You need to make these decisions based on knowledge and experience. You are the builder and you are responsible.

These decisions need to be decided on what parts you have in front of you. How is the oil feed to the rod bearings? What is the crank speed? Crank rotational speeds determine how the oil is feed to the rod bearings. What oil pressure you want at the bearings.

Oil directed straight off the mains does not require grooving but has shown good results. This type of design can withstand crank speeds typically seen in these Porsche engines. However, high speed cranks will be feed internally as ell. The later 991.2 engines are feed from the front nose as well. Porsche must have felt that the 9000 RPM required this. Race engines with crank speeds over 12000 RPM typically have center feed oiling due to the oil's inability to find its way to the rod bearings, due to centrifugal forces. All the high speed F1 engines I have seen had this oiling.

These Porsche cranks definitely in my opinion need all the help they can get to oil the rod bearings. To read the attached doc has to be done in reference to the type of crank in play and the engine type. To say its a blanket statement for all engines is in my opinion somewhat closed minded.

But to each his own I say.
Old 01-04-2020, 02:21 PM
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f1 files honda

Wow,what a great read.Piston pin clip and deformation of the groove is very real.PCA GT-3 running a 70.4 SC crank with 100mm bore splays the groove for the clip and needs a clean up when refreshened.I wonder what their Stromski tool looked like to put the clips in.Very cool.Piston clip cooling oil jets.
Old 01-04-2020, 02:33 PM
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Quote:
Originally Posted by faapgar View Post
I wonder what their Stromski tool looked like to put the clips in
Special tool that avoids disturbing the shot peening and nitrided surface!

Very cool read indeed! Thanks for sharing Speedy Squirrel

I see Honda resorted to 24 oil jets per piston. We only have one for our dinosaur Porsche engines? We clearly need to drill more holes in our case for more piston cooling.......

Hollow connecting rods in F1? Wow that's incredible considering how much abuse the rod is under.
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Old 01-06-2020, 08:46 AM
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The consensus from the builders I talked to is with air-cooled engines, the 76.4mm stroke Porsche Motorsports GT3 crank should not be drilled. Modify the case appropriately and use a GT3 oil pump and you will get the oil where it needs to go for an 8000 RPM engine.
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Old 01-06-2020, 09:38 AM
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The consensus from the builders I talked to is with air-cooled engines, the 76.4mm stroke Porsche Motorsports GT3 crank should not be drilled. Modify the case appropriately and use a GT3 oil pump and you will get the oil where it needs to go for an 8000 RPM engine.
You made my point, I guess. I suggested blanket statements that have been commonly used and thought, have no place in this business. That every engine and the parts used have to be looked at in entirety and not individually. This is what is needed in this community. There are many reasons to do certain mods. Every engine and its use will dictate what is done.

A GT3 crank is different to the early cranks too. Oil galley drillings are bigger, in fact the later cranks have to drillings on some cranks. Pump size is different, so in some cases, the center rods needs a little more help. The testing we have done on the Sprintron has shown it does help the early crank/rod supply.

I personally do not like the center feed oiling on these lower speed engines. Direct is better but this cannot be done on the earlier cranks. The overlap etc just will not allow it.

But the oil that is pushed to the main bearings from the pump has other difficulties to over come, even before it enters the crankshaft. GT3 oil pump or not, there is one major issue that should be taken care of as well. If not, it negates the larger pump and any cross drilling or grooving of journal or bearing shell.

I am including this is the paper about case assembly to come.
Old 01-06-2020, 09:57 AM
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Quote:
Originally Posted by Neil Harvey View Post
GT3 oil pump or not, there is one major issue that should be taken care of as well. If not, it negates the larger pump and any cross drilling or grooving of journal or bearing shell.
What is this one major issue?
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Old 01-06-2020, 10:05 AM
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So the grooving of the center main bearing is not to provide better main bearing lubrication but better oiling of rod bearings. Main bearings are generally not being taxed as hard (same bearings used in 400HP GT3). But getting oil to rods can be a problem. Picture below is from a old article showing oiling of stock 911, 908 and 917 crankshaft. The 911 at 9K rpm has lower pressure on center rods. For the 908 they had to raise the oil pressure to 100PSI to get the center rods oiled. The 917 had center lube and had better rod pressure at 10K with only 34psi. So drilling of main journal is to get more oil to the rod bearings furthest from the end when using engine at high RPM.





john

Old 01-07-2020, 12:30 PM
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