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Old 01-13-2022, 02:05 AM   #1
Hog Head
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Default Splitting case requires line boring?

I have a shop telling me that line boring is required once one splits a EJ20 case.
Seems to me that this is not the norm they are claiming...............

Any truth to this for a street application at 300 HP?
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Old 01-13-2022, 07:16 AM   #2
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Have them measure your main bearing bores.
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Old 01-13-2022, 07:42 AM   #3
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Perhaps I was not clear:
They are saying that once you split the cases on any and all EJ20 engines it MUST be line bored.

I am sceptical
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Old 01-13-2022, 08:09 AM   #4
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Quote:
Originally Posted by Hog Head View Post
Perhaps I was not clear:
They are saying that once you split the cases on any and all EJ20 engines it MUST be line bored.

I am sceptical
Subaru does not specify this unless you have issues with mains clearances. I can say I have built quite a few air and water cooled boxers in my 40 plus years as a tech and never had an issue.
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Old 01-13-2022, 08:32 AM   #5
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That theory is misinformation at best. The only reason they might think that is because sometimes the 2 locating pins either get bent when the cases are split, or the pins have too much clearance in the locating holes in the opposite case half. Either scenario will allow the halves to mis-align when bolting back together, so they appear to be whack when measured with a bore gage.
The correct procedure is to just snug the 10mm case bolts and then check the front and rear bores for mis-alignment at the parting lines. If the cases are shifted any, a tap with a dead blow will move them back into alignment before final torquing of the bolts. Obviously you can only do this with an empty block but on final assembly, the tight fit between the crank and bearings do their own alignment.
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Old 01-13-2022, 09:38 AM   #6
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Quote:
Originally Posted by Barney145 View Post
That theory is misinformation at best.
not sure how you can characterize that as misinformation at best.

I do believe that maybe it can be "tapped" back into place and be "close enough", but that recommendation certainly isn't misinformed. What they are saying makes total sense and they are basing it on guaranteeing perfect bores.
There's only one way to truly get perfectly round bores, and that is to do just what they are saying.
Is it maybe overly conservative?
sure, but not misinformation
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Old 01-13-2022, 11:06 AM   #7
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Assuming no problems with the bearing bores, and since I only boring the cases for pistons, I do not see why line boring the mains is a requirement when splitting the cases.
The FSM seems to agree.

Where this dictum falls apart is that after line boring, the cases are once again split in order to assemble the engine, so back to the beginning - sort of like Groundhog Day.
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Old 01-13-2022, 11:16 AM   #8
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Quote:
Originally Posted by Hog Head View Post
Assuming no problems with the bearing bores, and since I only boring the cases for pistons, I do not see why line boring the mains is a requirement when splitting the cases.
The FSM seems to agree.

Where this dictum falls apart is that after line boring, the cases are once again split in order to assemble the engine, so back to the beginning - sort of like Groundhog Day.
I agree with you, but it falls to "how do the mains look" after splitting/reassembling and measuring. A good number of Subaru blocks are not perfectly true from the foundry so a hone is not uncommon. I've had blocks be true and not require work though so it really just takes a good machine shop to tell.

But yes, once you split a block that's already been honed/bored it's not required to do so again. Measuring is the key and to do that requires multiple assemblies of the block.
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Old 01-13-2022, 11:48 AM   #9
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I strongly recommend it on USED cases where they have been heat cycled over and over again. Despite being bolted together things will have shifted a bit over time, and if you're rebuilding it then it's best to make sure everything is true.

On NEW cases a line bore not necessary UNLESS I am building an engine where precision is a key factor of the build. For example, daily driver street driven motor - not necessary. Track motor where you need everything spot on and there's not room for compromise - necessary.

Now, I know everyone is telling your to measure the mains, and you should, but there's something being lost in that statement. Yes, absolutely measure your mains, BUT ALSO make sure they are straight from one end to the other. Measuring one bearing at a time to check for round is just half of it.
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Old 01-14-2022, 06:07 AM   #10
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Quote:
Originally Posted by rtv900 View Post
not sure how you can characterize that as misinformation at best.

I do believe that maybe it can be "tapped" back into place and be "close enough", but that recommendation certainly isn't misinformed. What they are saying makes total sense and they are basing it on guaranteeing perfect bores.
There's only one way to truly get perfectly round bores, and that is to do just what they are saying.
Is it maybe overly conservative?
sure, but not misinformation
The misinformed is splitting the case Requires a line bore.

FWIW: Barney has probably done more line bores on subarus than anyone else.
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Old 01-14-2022, 12:10 PM   #11
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I didnt have my mains line bored, and when I measured clearances by bolting the heads on with my ARP 625+ headstuds, my mains were all over the place but within my tolerances. This was on a seasoned block as well:

1 .0015
2 .0016
3 .0015
4 .0015
5 .0018
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Old 01-14-2022, 03:11 PM   #12
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Main clearances can come out normal but the bore can be crooked. That's the reason for a line hone or bore. In my post I assumed people knew the difference between measuring individual mains vs measuring front to back straightness. That's why splitting a case isn't a big deal once you've confirmed the mains are true.
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Old 01-14-2022, 03:20 PM   #13
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Quote:
Originally Posted by subydude View Post
Main clearances can come out normal but the bore can be crooked. That's the reason for a line hone or bore. In my post I assumed people knew the difference between measuring individual mains vs measuring front to back straightness. That's why splitting a case isn't a big deal once you've confirmed the mains are true.
ah, well I definitely learned something then. I did not do this on my block, but oh well haha.
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Old 02-15-2022, 09:28 PM   #14
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Can someone describe and hopefully show pictures of a method to measure the locations of the main bores? All the methods of which I can think involved coordinate measuring machines which I don't have.

I know with a V8 some people will lay a known straight rod across the bearing housings and use a feeler gage. This doesn't really seam feasible for an EJ.

I think the EJ, with the short crank and close bearings is quite sensitive to the main bearing location due to the geometry. Simple math that doesn't take into account the real compliance of the oil and the crank shows that the .0005 tolerance between two adjacent bearings that King and Clevite mentions might not be acceptable for an EJ, certainly not one with OEM clearances.

From what I have read people don't measure on a "seasoned" case, they just align bore to make sure things are good. My last engine I just took apart due to a cracked liner has main bearings that show wear consistent with them not all being on the same axis. This was a seasoned engine, and all clearances were set to what I intended (upper end of OEM).
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Old 02-16-2022, 09:22 AM   #15
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There really is no way to check for that accurately, as the cases halves need to be torqued up before alignment can be checked. A laser system maybe but nothing easily purchased. I can't attach the video here but if you go to Youtube and type in " Subaru line bore explained " it addresses this problem. Unfortunately Motion is no longer doing any Subaru work for the general public.
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Old 02-16-2022, 11:19 AM   #16
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Ya, I understand about the case needing to be assembled and torqued, hence my question. I will search for the video. I was hoping someone figured out easyish way. I was thinking perhaps when on the boring machine you could measure with respect to the boring bar somehow.

A laser alignment system will not be useful because they are really only good for pointing (angle). For the angle measurements you'll get a significant displacement of the laser on the target for an angle of a bore. For position measurements the displacement of the laser would only be the same order of magnitude as a displacement of the housing bore which might be one thousandth of an inch or so.

I think if someone had a coordinate measuring machine you can measure the housing locations with a long probe or a right angle probe.
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Old 02-16-2022, 11:33 AM   #17
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That video is here: https://youtu.be/KnjliZ2QTM8
That is a shocking amount of misalignment (based on the observation of cutting). At least .003" out of line!

I don't think I would undertake milling the case halves and then re-boring It seems like a lot of cost and effort when new case have are about ~1100. I think I'd go the over-sized bearing route so rear seal bore and deck height and oil pump dowls all remain the same shape, size, and location.

Is it reasonable to say: don't use used EJ cases without an align bore?
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Old 02-16-2022, 02:26 PM   #18
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Donít check clearances or ask questions you dont want the answer to.

I have never had the mains shot before, has yet to be an issue
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Old 02-16-2022, 06:25 PM   #19
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Any serious competition engine making real power will eventually pound out the mainline. Street vs competition is apples and oranges. The misalignment can be measured with the setup dial indicator in that video but that's a lot of setup just to check a block. Anytime ARP case bolts are used, the block needs line boring and competition blocks always get ARP bolts, hence the insane number of line bores that Motion has done. Re-machining the rear seal diameter is part of the process. Pump dowel holes eventually need opening up if you have to cut a block too much. And deck heights are also reduced but cutting piston domes is easily done. If you have a sleeved block, it is obviously cost effective to line bore instead of replace.
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Old 02-17-2022, 01:43 AM   #20
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Quote:
Originally Posted by Barney145 View Post
The misalignment can be measured with the setup dial indicator in that video but that's a lot of setup just to check a block.
This is what I have suspected. It generally isn't done, because it is a lot of work for these engines and in applications where it matters, the line bore is done as a matter of course (like when ARP case fasteners are used). That also makes sense about boring vs. replacing if the block has significant investment in other improvements.

Why not overbore the main bores and use King oversized bearings rather than cutting the case then boring?

when I opened my case this last time I was surprised at the bearing wear consistent with misalignment and that caused me to go looking for ways to measure. I would love to know the level of misalignment. I did have the clearances at ~.002" and wanted to understand more about what happened. Were the clearances too tight given the misalignment? Engine didn't fail due to this but I suspect longevity would have been impacted.
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Old 02-17-2022, 07:44 AM   #21
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"Why not overbore the main bores and use King oversized bearings rather than cutting the case then boring?"


Definitely an option, many have been done that way. Some race teams have special made main bearings that are available only in standard housing diameter.
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Old 02-17-2022, 09:16 AM   #22
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Quote:
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Definitely an option, many have been done that way. Some race teams have special made main bearings that are available only in standard housing diameter.
Thanks for the explanation! I had been wondering about that for a bit.
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