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Does the case sealant used effect bearing clearance and oil pressure?

Searched a lot of the old threads, interesting reading. Lots of threads on spun bearings, presumed due to low oil pressure.

One thread, quoted below, mentions that a lot of folks lose oil pressure to their rods due to excess bearing sealants. The sealants effect bearing crush for the thrust bearing, causing up to .005 increase clearance and therefore low oil pressure.

The article is referring to anaerobic sealant, which is quite thin. I would think that the Loctite rubber (1104?) would be waaaay thicker. Some of the pics I see show folks putting the Loctite 1104 on fairly thick. Some to both sides of the case.

Anyone have thoughts on this? Non issue?

Does the anerobic sealant, even though more likely to leak, cause closer clearances than using Supertech Sealing kit with Loctite 1104 (or whichever)???

I did measure my case bores at various torque levels on the case. The difference between 16 ft/lbs and 26 ft/lbs was .004-.006 greater bearing compression. Meaning, clearance went from .0028 to .0022. So, small differences make a huge difference in clearance...

Thoughts?

Quoted:

Yup, here is an exerpt from Greg Browns article on the subject in "Velocity" the Porsche Owners Club magazine

"how a 911 crankshaft gets oil. The oil for the main bearings comes through a passage that runs from the rear of the case to the front of the case. Each main bearing is fed off of this passage with another passage to each and every bearing. The rod bearing oiling, however, is not quite so simple. The rod bearings are fed oil from the very front (clutch end) of the engine and from the very rear of the engine (pulley end). The pulley endís main bearing is refered to as the #8 bearing. The flywheel end is also the bearing that controls the thrust of the crankshaft back and forth (end play). The oil then travels through the entire length of the crankshaft and each rod journal is fed oil from this channel. It is important to note that oil is fed from both ends of the crankshaft for the connecting rods. On initial inspection of the oil system,
one would think that the #3 rod bearing (closest to the front and closest to the oil pump) would get the majority of the oil. Not true. To understand this, one must understand how oil (or any fluid) behaves when it is fed through channels to the crankshaft. I think that class on fluid dynamics is where I learned this, but maybe it was when we were trying to get that giant water bong to work. (Since I canít really remember, it was probably from the water bong thing.) At any rate, fluids tend to back fill. This means that the oil will flow down the main passage and then start to back up and fill the small passages once resistance is met on the far end. So, the oil passes down the channel of the crankcase to the #8 main bearing, where resistance is met from the passages that feed oil out to the heads. Here, the oil begins to back fill and the crankshaft main bearings and the rods bearings get their oil.
From this, it becomes easy to understand which bearings fail first when there is a lack of oil on an intermittent basis. Itís really very simple: #3 rod bearing fails first and is followed by #4 in a 911 engine. In a 944 engine, #2 goes first. In a 928, #6 is the first one out of the block. Engine failures get really easy to figure out from this. If you lose any other rod in a 911 engine, it is not from a lack of oil, but must be sourced from another problem, like detonation. 911 engines frequently lose the #5 rod first
(especially the turbos). This is because this cylinder runs the hottest and starts the detonation process soonest. The small detonations donít ever show up on the top of the piston, but just hammer on the rod bearing, causing this failure. (There are addditional clues for this failure, by the way) So, if youíve blown up an engine and #5 was the one to go and your mechanic blamed it on the oil system, you better talk him into taking a few degrees of timing out of the engine before you have another vent in your
new engine. This, of course, is only true if you have oil. If you lose all the oil at once and donít see your oil pressure gauge or the waving black flag, all bets are off. The rod bearing that sticks first, spews parts first. The final thing to understand is how a 911 engine case is machined. This is pretty simple for this discussion. The main bearing bores are machined perfectly round to a specific dimension with the case bolted together. The aluminum surfaces where the case halves bolt together are bare aluminum. This is true when the case is made at Porsche, and hopefully is true after any subsequent machining processes take place. As you can see from our picture of a GT3RS case going together on the engine stand, the front main bearing (flywheel end) and the #8 main bearing are surrounded by aluminum that has to get sealant in order for the case not to leak. Enter Mr. Flood OíLoctite. (See picture of crankcase with sealant.) Since he canít squeeze the excess out, the case is held apart in these areas. Iíve actually measured Loctite .005Ē thick in these areas. What do you suppose this does for the bearing clearances? Well, they just go nuts and youíre lucky if you can get half of the oil to the rod bearings that should be going there. Combine this with the wrong rear thrust bearing (going to get to that, too) and you have a recipe for disaster. So here is the absolute proper way to use Loctite 574. Use a short nap roller that has been rolled full of Loctite 574. Make sure that the Loctite is fresh. This stuff still looks good when it gets old, but it hardens faster. We donít keep any open bottles longer than 6 months. We also do not keep the roller for any longer than 3 months. Roll on a thin layer on a completely clean, grease free case. Tighten the case halves together as fast as possible once they have contacted each other. Now, hereís a top secret tip that Iím going to let you in on, but donít tell anyone else! Tighten the perimeter case bolts first, especially on a late engine with ďo-ringsĒ that have to be slid over the case bolts with a special tool. This will squeeze out the excess Loctite before it gets a chance to start to harden. If you do the big bolts first, the perimeter may start to ďgo offĒ before you get to this hardware, especially if youíre a bit slow. If you do it this way, youíll never have a problem. Last thing to mention here is the main bearings themselves. Buy the main bearing set from Porsche. It comes
complete with the #8 main bearing in a box for $154.02, retail. The outside suppliers will sell you a set cheaper, but it will not come with the #8 main bearing, which you will need to buy separately. This will cost you more money than if you buy the complete set from Porsche. Not only that, but the main bearings from the outside suppliers have the wrong rear thrust bearing! If you look at the pictures of the thrust bearings, you can see that the aftermarket supplied rear thrust has straight grooves that pass the oil onto the thrust surfaces and allow the oil to escape without any resistance. Now look at the Porsche thrust bearing. Note that the oil grooves are cut notches that do not communicate with the outer edge of the thrust area. This keeps the oil more captive and thus
keeps more oil heading towards the rod bearings. This is the same thrust bearing that is recommended for all of the Porsche race engines, the only difference being that Porsche pays no attention to the size of the rear thrust bearing for street engines. The race engines have three different size rear thrust bearings that can be used, depending upon what size the crankshaft is. You had better get these the correct size, with the engines turning over 8,500 rpm. Of course, Mr. Flood OíLoctite used the wrong thrust bearings in the race engine we just took apart, but at least he only charged $265.00 for the complete set. "

Both cars were tracked, the theory is that the owners may have cranked in too much ignition advance for the gas/conditionns
Old 11-10-2017, 08:52 AM
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I've heard the argument that using 574 in the webs effects main bearing crush, the above seems to anecdotally cite the same thus their recommendation to only use a very thin layer applied by way of roller. The best way to test this would be to assemble a block minus crankshaft, but with bearings and 574 in the webs then measure. Might be worth it to know for sure, because any additional clearance is not welcome.

That all said, I have spoken with Loctite engineers and they are not of the position that 574 is the most optimal stuff to use on the webs anyway, they advise it is a flange sealant and can be used on the perimeter but in the webs as a 'glue' is out of its scope. Rather they suggest a retaining compound of much thinner viscosity to be appropriate.

I believe Henry would be the most appropriate individual to comment on this as he's been using 574 at the webs for some time as I understand. With the volume and quality he is known for I believe he would know before anyone
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Last edited by lvporschepilot; 11-10-2017 at 09:56 AM..
Old 11-10-2017, 09:49 AM
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Quote:
Originally Posted by lvporschepilot View Post
I've heard the argument that using 574 in the webs effects main bearing crush, the above seems to anecdotally cite the same thus their recommendation to only use a very thin layer applied by way of roller. The best way to test this would be to assemble a block minus crankshaft, but with bearings and 574 in the webs then measure. Might be worth it to know for sure, because any additional clearance is not welcome.

That all said, I have spoken with Loctite engineers and they are not of the position that 574 is the most optimal stuff to use on the webs anyway, they advise it is a flange sealant and can be used on the perimeter but in the webs as a 'glue' is out of its scope. Rather they suggest a retaining compound of much thinner viscosity to be appropriate.

I believe Henry would be the most appropriate individual to comment on this as he's been using 574 at the webs for some time as I understand. With the volume and quality he is known for I believe he would know before anyone
I would think that the 574 is pretty watery, and less likely to cause build up...

The Loctite/hondabond equivalents are pretty thick... I could see how these would effect tolerances... Especially around the thrust bearing that feeds the rods...

Clearly many engines have been built using the stuff...

But you also see lots of threads along the lines of "why does my new engine rebuild have lower oil pressure than I expected?"

Curious what the pros think also?

Again, suspect its a non issue, but I can see how a thicker sealant like hondabond might effect clearance...

When folks put this stuff on, is it on both sides of the case or one side? I found some threads that mention if you only put it on one side you have a higher rate of leaks...
Old 11-10-2017, 10:42 AM
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Bo,

You seem to have an abnormal fascination with oil pressure that spans multiple threads. To answer your question, 574 is applied to only one side of the case. That is the standard, accepted practice and after building dozens of engines I have never had any issues with this method.

The reason you want 574 is that in an oxygen environment, it stays soft forever. Try it sometimes - leave a tube of 574 uncapped. It will still be soft and usable after a year.

What this means to you as an engine builder is that any EXCESS 574 stays soft and is gradually washed away by the oil and then becomes an irrelevant non issue.

Where it's supposed to go - namely the case parting line - it cures to a nice leakproof finish that does not impart any extra strength or stiffness. When the case halves are squeezed together and tightened, there is very little gap that the 574 fills. The 574 thickness in this case would be measured in microns......

So no, there is really no way that 574 would influence bearing clearances. It has no inherent strength and most of it is lost to squeeze out.
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Old 11-10-2017, 12:14 PM
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Quote:
Originally Posted by Catorce View Post
Bo,

You seem to have an abnormal fascination with oil pressure that spans multiple threads. To answer your question, 574 is applied to only one side of the case. That is the standard, accepted practice and after building dozens of engines I have never had any issues with this method.

The reason you want 574 is that in an oxygen environment, it stays soft forever. Try it sometimes - leave a tube of 574 uncapped. It will still be soft and usable after a year.

What this means to you as an engine builder is that any EXCESS 574 stays soft and is gradually washed away by the oil and then becomes an irrelevant non issue.

Where it's supposed to go - namely the case parting line - it cures to a nice leakproof finish that does not impart any extra strength or stiffness. When the case halves are squeezed together and tightened, there is very little gap that the 574 fills. The 574 thickness in this case would be measured in microns......

So no, there is really no way that 574 would influence bearing clearances. It has no inherent strength and most of it is lost to squeeze out.
As always, appreciate your input...

I know I am overthinking all of this... Its just my nature . I love to question and learn.

As I posted tons of threads ago, my oil pressure in my tracked 930 is fine based on the Porsche 930 manual... 4 bar or 60 psi or so over 3000 rpm.

I would love to get to the mythical 5 bar some on here seem to get to. Just trying to make sure there aren't any oil pressure losses somewhere in my case before I button it up...
Old 11-10-2017, 12:51 PM
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I get 5 bar cold when you bring the engine off idle and as low as 0.8 bar at idle when over 100* outside.
Old 11-10-2017, 01:23 PM
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Quote:
Originally Posted by Tippy View Post
I get 5 bar cold when you bring the engine off idle and as low as 0.8 bar at idle when over 100* outside.
This.
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Old 11-10-2017, 01:25 PM
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By The way, Bo, what issue of velocity was your quote from?
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Old 11-10-2017, 01:36 PM
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Originally Posted by Catorce View Post
By The way, Bo, what issue of velocity was your quote from?
It was quoted from an 8 year old thread... no date listed?
Old 11-10-2017, 01:38 PM
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Oh OK just curious is all no big deal.
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Old 11-10-2017, 01:48 PM
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Quote:
Originally Posted by Tippy View Post
I get 5 bar cold when you bring the engine off idle and as low as 0.8 bar at idle when over 100* outside.
I have owned 3 911's (76 911s, SC, 930...well 4, and a 996)...

None of mine did that, ever.

Idle is 1.5 bar +/-. Hot/warmed up, 3000+ rpm is 4-4.2 bar and that's where it peaks. That's with 20/50.

Porsche 930 WSM specs 4 bar at 5500 RPM at 80 degrees... I easily have that... (at 3000-4000RPM+)

I have reads hundreds of threads on here, most stating this is normal. Yet others claim much higher pressures. There was one thread where a poster electronically plotted pressures, and they exhibited the exact same curve, albeit he reached 4.5 bar or so.

Checked:
1) Manual gauge verified
2) Bearing clearances (normal, but were on the looser side) (Bought new bearings and they were thinner than the old ones...)
3) Relief pistons/springs, shimmed, etc
4) Oil pump opened, visually looks "ok"
5) External lines
6) green seals looked "ok" no rips

Even absolutely ice cold, at idle, pressure shoots right up to 4 bar for a millisecond and then drops immediately to 3.5 bar. I can apply throttle, again, ice cold, and it goes to 4 bar.

Its literally like the oil pressure relief opens at 4 bar and that's it.

My 911S did exactly the same thing... albeit that one had 130,000 miles.

That's why I am just wrecking my brain trying to make sure I am not missing anything before putting it back together...

Perhaps its just that the bearings were slightly worn (though measured fine). Checked with micrometer, measured good. Thought I have read threads where folks ran with absolutely shot bearings and spun bearings and oil pressure was "great."

So, just trying to cover my bases...

Figure there has to be some magic I am missing if others are getting 5 bar at just over idle...

Thanks for letting me vent

For those folks getting 5 bar just off idle... what are your bearing clearances??? Are you running .001-.0015 or something similar? That would explain it. I guess there could be some variation in oil pump max pressures...

I did have my rods resized also. I didn't measure clearances before doing that. It is possible my rod clearances were loose or stretched. The old bearings measured in spec. New clearance are .002 to .0025...

I do hope this info helps others. Especially noting (as others have before) that the new bearings are thinner than the old. If someone just popped in new bearings and increased their clearance .001, that would almost certainly lower their oil pressure...

Just enjoying the journey

Last edited by bpu699; 11-10-2017 at 02:14 PM..
Old 11-10-2017, 02:05 PM
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Originally Posted by Catorce View Post
Oh OK just curious is all no big deal.
Here is the thread if its helpful...

What # Rod Bearing failure is most common?
Old 11-10-2017, 02:13 PM
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Bo, I didn't check clearances other than measuring the journals which came in dead nominal.

Slapped my new Glyco's in and never looked back.
Old 11-10-2017, 06:35 PM
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I am not sure that 'spun' bearings are the result of low oil pressure.

It is much more likely that oil starvation is the cause or that the crush was incorrect.

Trying to compare pressure on a number of engines where there is little or no accompanying data is also likely to be misleading and likely to cause more confusion as it is almost impossible to know anything about the quality of the measurements.

Pressure relief valve springs will vary and they will lose around 10% of their nominal stiffness at 100 degC so their 'set point' will vary as the engine warms up.

The installed length of the spring will also vary and this will also result in variations.

If you audit all of the uncertainties of the measurements being made and all the variables in terms of oil viscosity variation with temperature you may well find some of the answers you are looking for.
Old 11-12-2017, 02:28 AM
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Quote:
Originally Posted by chris_seven View Post
I am not sure that 'spun' bearings are the result of low oil pressure.

It is much more likely that oil starvation is the cause or that the crush was incorrect.

Trying to compare pressure on a number of engines where there is little or no accompanying data is also likely to be misleading and likely to cause more confusion as it is almost impossible to know anything about the quality of the measurements.

Pressure relief valve springs will vary and they will lose around 10% of their nominal stiffness at 100 degC so their 'set point' will vary as the engine warms up.

The installed length of the spring will also vary and this will also result in variations.

If you audit all of the uncertainties of the measurements being made and all the variables in terms of oil viscosity variation with temperature you may well find some of the answers you are looking for.
Found some interesting articles on the internet...

The average bearing only sees 2lbs of torque at max RPM in a race engine!

Bearing crush should provide 100x that as a safety margin (the tabs also help, I am sure).

New bearings have a crush of about .004...

Just some interesting factoids...
Old 11-14-2017, 08:05 AM
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Wow, that's pretty low, but makes sense. If the bearing is moving at all, you have problems.
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Old 11-14-2017, 08:30 AM
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