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01-27-2009, 11:59 PM | #1 |
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Nasty cam journal
Just tore down my ej22g hybrid block in preparation for the new cams and rods, and I came across this:
Looks like particulate damage to me... but the real question is, are the heads garbage? I'd rather not have to try and source new heads, but I'll do whatever it takes. I'm trying to max out my TD06H-20G, so 450-480chp, and up to 7800rpm.
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01-28-2009, 12:20 AM | #2 |
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You can have a machine shop line bore the cam journals. They remove a small bit of material from the cap base and then line bore back to proper bore. Its expensive but it works. For what its worth that pic isnt too bad, I have seen way worse. The load is much less than what a engine bearing sees on the rods and mains. It does see some load from the valve springs but not comparable.
Honestly I would just use a very fine croachas cloth and hand polish it. If you really concearned take it to a machine sop and have them mic the bore and check what the max tolerence is... |
01-28-2009, 12:48 AM | #3 |
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We have a machine shop at the auto parts store I work out, one of the only ones in the city, but they mostly do factory rebuilds and SBC builds, I'm pretty sure I've supplied them with half the subaru motors they've worked on
Maybe I'll fire off a pic to Jon at delta... he did my cams afterall. |
01-28-2009, 12:06 PM | #4 |
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Get a new head. The info given above is false and you will damage your engine if you will reuse them. How are the other bearings(main, rods) look like?
Artie |
01-28-2009, 12:30 PM | #5 |
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Jon at Delta had to line bore my head as well after a failed rod bearing. Material gets into the oil pathways and then eats the journal. The only real way to do it however is to undersize the journal and then weld on extra material to the cam.
This mates the cam to the head forever... |
01-28-2009, 12:48 PM | #6 |
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for us noobs, can you please explain what is damaged... I like to learn things everyday.
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01-28-2009, 01:47 PM | #7 | |
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Haven't gotten into the shortblock yet. Ryan West: The cam journal is the oiling surface for the cams, cams in subaru engines dont ride in bearings, they're not generally much of a wear surface. |
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01-28-2009, 02:03 PM | #8 |
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Your head might not be toast. Look at the underside of the cam cap that goes over that journal... because its the cap that bears all of the load. If it is worse than the bottom half, then it might be questionable.. in which case I'd look into having it repaired by a competent machine shop.
Polish up the marking by hand with grey scotch brite... don't dig in much; just remove the high spots. Then dab some oil in the lournals, install the cam (torque it up with the other cam caps too) while it's completely disassembled. Check to make sure the cam spins freely by hand. Setup a dial indicator on the top of the cam, then move the cam up and down. If there is more than .002" of deflection, the head needs to be repaired or replaced. If not, i'd say run it. There should also be .003" to .005" of cam end play as well. It would be a good idea to remove all of the oil galley plugs on the head(s) and make sure the oil galleys are clean/free of debris before you think about re-using them. I'd get an upgraded oil pump while you are at it too.. .02 It would also help to upgrade the oil pump while the engine is apart too.. |
01-28-2009, 02:38 PM | #9 |
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I'm running a 10mm oil pump, I dont think it's necessary to run bigger than that for my setup (no avcs)
I'm bringing it to a machine shop this afternoon for them to look at. |
01-28-2009, 05:29 PM | #10 |
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machine shop says its repairable
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01-28-2009, 05:48 PM | #11 |
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since im new at this, id still like to know what im looking at that needs to be fixed. can someone school me please?
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01-28-2009, 06:46 PM | #12 |
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It's actually very simple. Cams are kept in place by cam journals. Cams are rotating parts in the head and to reduce friction they are lubricated by oil. Cam journals should have a very smooth, mirror type surface. Journals are part of the head casting. Subaru recommends to keep oil clearances (difference between inside diameter of cam journal and outside diameter of cam) somewhere between 0.037 — 0.072 mm. If the clearance is too big, oil will have less resistance on it's path and oil pressure will drop as a result. If the oil clearance is too small, the parts will not get enough oil to keep them lubricated.
Hope this will help |
01-28-2009, 08:31 PM | #13 |
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Yes we know artie, You said the process I described above wont work yet I have seen MANY reline bored and look good as a new head because it will be machined and its the same process the factory uses and the finish dia will be in spec.....
http://www.enginebuildermag.com/Arti...g_subject.aspx A good read for you to educate yourself... And yes I have worked in a machine shop that did the process. Its the same setup as reline boring a block for a crank just in a smaller scale and ra has to be finer... |
01-28-2009, 08:59 PM | #14 |
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If it was trash in the gallerie it would also be scuffed in line with the oil feed holes. The area past the feed holes looks ok. It seems to me that the head may be warped. That looks like it will take .010 cut to clean it up minimum. Maybe .020 that means the cam will be .010 or .020 closer to the valve stems. That means either all the stems will need to be shortened or new .010 or .020 thinner buckets. That also means the cams will rotate a little in the advanced position. Has anyone tried welding the journal up and putting it back to original? I would rather do that than have a perminately crummy head.
When you line bore a vw and I think a v8 there are replacement oversize bearings that fill the new gap and the crank or cam stays in the same place, not so on the suby the cam is now closer to the valves forever. A line bore on the cam bores can look great to the eye as it's now nice and shiney but that doesn't make it a good repair. That will also limit the amount of lift that cam can run before coil or seal bind on the valve. If they are 1500.00 heads I would try to get the journal welded and re bored to stock. If they are 250.00 heads do the cheapest repair. Last edited by charliew; 01-28-2009 at 09:26 PM. |
01-28-2009, 09:53 PM | #15 |
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I really don't think it's warped heads for a couple reasons... You can see where grains of something caught and pulled on the aluminum.
The reason that there is a clear line around the oil grove is that on the cam surface, there is a matching machined groove. There is no contact in that area. |
01-28-2009, 10:05 PM | #16 |
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Sorry I was looking at the cams in the pictures above. I didn't remember any grooves in the cams I've worked with. It seems that the cap would also be rough. It's like the bore wasn't round. Maybe it was put together real dirty. Do you think plastigage could have been left in it? Usually you would lay the plastigage on top of the cam and put the cap on though.
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01-28-2009, 10:09 PM | #17 |
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V4 STI cams
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01-29-2009, 07:24 AM | #18 | |
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01-29-2009, 10:04 AM | #19 |
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Here is what I would do based on my own hands on experiences with rebuilding ej20 motors (my personal motors)...
First establish a baseline by measuring the cam/journal clearances of the non damaged journals. Line hone the subtracted difference from the factory absolute limit and then see what you have. After line honing, if the journal surface still looks quite rough, I would then trash the head as previously suggested by Artie rather than continuing to remove more material. Why take the chance with a "high reving application?" Personally, I would be worried about the excentric forces and early wear issues created by excess clearances within the journals, not only to the journals surfaces, but also to the cam lobes and buckets. Hidesight can be a real beotch.. Good luck, Tom. |
01-29-2009, 10:26 AM | #20 |
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Well the shop says that they can machine rod bearings into the cam caps if necessary, which is expensive but it's better than stock, because after that, it becomes dead easy to replace them down the road.
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01-29-2009, 10:43 AM | #21 | |
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Please keep this thread updated because I would love to add your experience to my memory banks for future reference. Tom |
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01-29-2009, 02:33 PM | #22 |
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I haven't had any headwork yet, I'm running the 98 DOHC/V4 STi heads, which outflow any of the north american turbo heads by a margin from the factory.
The problem is tho, if the machine work is $400, and another set of used heads is $300, I might end up just inheriting someone elses problem, plus all the work of setting up the DOHC NA heads for turbo |
01-29-2009, 04:06 PM | #23 |
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The managed to repair it, oil clearances are now at .055mm across the board.
They took about half a thou off the bottom of the caps, so the journals are very, very slightly elliptical, but these guys ahve been building high revving engines for years and they said it won't be a problem, especially with the super short subaru cams. |
01-29-2009, 09:17 PM | #24 |
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I guess what alot of people are missing is that the caps will be slightly machined at thier base to close the bore, then it will be relined to oe specs. Now yes the cam will sit closer to the valves but it will be half of whatever is removed. So if you close the bore by .020" then after reline the cam will be effectively .010" closer to the valve (this is only in the ballpark as thier are machining tolerences that can effect the final measurement).
Now on to the other issue, the valves on most aftermarket suppliers ship thier valves long to be machined to the use on the head. Plus thier are different bucket sizes to help setup clearences.. This is how most subie heads undamaged are setup with aftermarket valves.. This end result is basicly all in the machinist and engine builders hands and can be made good as new with an experienced machinist... |
12-21-2019, 12:20 PM | #25 | |
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