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Old 02/24/18, 11:00 AM   #46
nvrstuk
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20 gears forward...no reverse!

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Ok, gotcha...

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Old 02/24/18, 07:22 PM   #47
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One other thing to look into, check the oil drain back holes from the heads to the block, if they do not line up well, it could be flooding the valves.

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Old 02/24/18, 07:36 PM   #48
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Quote:
Originally Posted by pcf_mark View Post
My only fear with pulling it out is if you do not KNOW what it is and you spend the time and money and it still does it. All that and you have a blocked return port in the head flooding the head with oil over coming the valve seals or something would hurt.
I don't see much to fear. He has been chasing his tail for 2 years had the heads off and rebuilt and no change. Everything points to rings. At least to me. Especially with the latest revelation of pistons rocking in the bores. Why keep messing around it needs to be torn down and inspected. In which the problem should be found if its something simple then it only costs some gaskets and time. Trying to guess without tearing it down keeps him in the same tail chasing circle

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Old 02/24/18, 11:55 PM   #49
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Well I got the engine pulled out and the heads off tonight, it was the rings. Every cylinder had oil pooled up in them, with a big sludge spot dead center of each piston. Also, the pistons moved back and forth easier inside the cylinder than last time. I can see a couple smooth spots where the cross-hatching has worn off, so Ill be taking it to a shop this week to get everything checked out. I did notice a couple extra issues, my head gaskets were partially blocking one of the drain holes on each head, and one of the intake gaskets was already failing at an intake runner (one week old), but the rings look to be the largest culprit, and maybe the pressure that was creating was causing the intake issue b/c it was starting to spread oil around inside the head gaskets as well. I'll be pulling the pistons out to see what the rings look like, and hopefully I can see what went wrong with maybe 2500 miles on them. Thank you for all the ideas, I really appreciate it.

Ryan

77, 351 full roller, GT40X heads, headers, NV3550 w/ Twin Sticks, WH 2.5" SL & 1" BL, 33" BFG KM2s, 4.56s, under construction..
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Old 02/25/18, 12:53 AM   #50
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I would assume part of that process would be verifying that the pistons are the correct size for the bore. Was this one bored oversize the last time it was gone through?
Sorry I didn't re-read through it to see if that was already covered.

Paul

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Old 02/25/18, 12:53 AM   #51
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Nevermind. Reviewed your first post and it says .030" over.

Paul

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Old 02/25/18, 01:02 PM   #52
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Ooooof. Hone and new rings. Super duper careful reassembly.

Can you carefully take the rings off an shoot some pics before / during / after?

My wife and my Bronco are not friends...
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Old 02/25/18, 02:16 PM   #53
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20 gears forward...no reverse!

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Good luck!! Hope you're up and running soon...

Strrroker powered... 418 cubes, 518 HP, SEFI, EDIS, Still 20+ forward gears...CB build:http://classicbroncos.com/forums/sho...d.php?t=278607 NWCB Stroker/SEFI/EDIS/4r70W/KluneV/TrueHi9 build: http://northwestclassicbroncos.com/s...n-to-SEFI-EDIS
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Old 02/25/18, 03:30 PM   #54
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This may seem silly, but I had a massive oil burning issue too, ended up being the valve covers. The valve covers themselves did not have a splash gaurd at the pcv. So oil was getting sucked through the pcv and burned through the intake...
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Old 02/25/18, 05:13 PM   #55
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I've been taking the engine apart and cleaning parts, and I pulled the #1 piston out and pulled the top ring off to check it in the bore. At 1" down from the top, it measures about a .020 gap, which seems to be at the top end of spec? But the pistons are still moving in the bore, so does that mean my rings aren't matching the pistons even though they are made for 4.030? I read there's a difference between metric rings and standard on 351s, but since I replaced the factory pistons with KB ones, I didn't think that was relevant anymore. I'm thinking about leaving the rest of the pistons in there and taking it to the shop as-is, so they can check everything out as it sits and maybe pinpoint the issue. What do ya'll think?

Mark, I've taken some pictures but haven't renewed my contributor status yet, once that's back up I can upload them.

Monster, I actually put the factory valve covers back on with the massive baffles in there in one of my attempts to fix this issue.

77, 351 full roller, GT40X heads, headers, NV3550 w/ Twin Sticks, WH 2.5" SL & 1" BL, 33" BFG KM2s, 4.56s, under construction..
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Old 02/25/18, 05:18 PM   #56
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There should be pretty tight clearance between the piston and the bore, only a few thousandths. If the piston can rock around that much the rings aren't going to be very effective.

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Old 02/25/18, 06:08 PM   #57
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The pistons should be marked as to size (mine were). What size are they?

As I recall (don't have my build sheet in front of me), all my rings were 17 thousands one inch in the bore. The pistons were tight no rocking.

I'm guessing the pistons are the wrong size for the bore....

Tim

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Old 02/25/18, 08:49 PM   #58
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The pistons are marked .030, my rings are .017 right at the top of the cylinder, but open up to .020 once its down in there an inch. With the #6 piston at TDC (just picked one), I have roughly a .021 gap, measured with a feeler gauge. This was my first engine to build, so I have been learning as I go with it, and assumed the parts I received were accurate.

77, 351 full roller, GT40X heads, headers, NV3550 w/ Twin Sticks, WH 2.5" SL & 1" BL, 33" BFG KM2s, 4.56s, under construction..
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Old 02/25/18, 09:00 PM   #59
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20 gears forward...no reverse!

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Cylinder bore appears o harbored or honed or the pistons are the wrong size...take it to your or an engine builder. They can see or measure quickly and easily what we are just making educated guesses about.

A piston should measure depending on several factors between .0025-.005" smaller diameter than the cylinder bore... that said, if you are pushing the ring into the bore squarely-with a piston NO WAY should you have that much taper difference in the bore (you are measuring ring gap correct) with the mileage you ha e put on this engine. Heck, an Exploder engine with 280K miles wont have that much cylinder taper...

Please note I'm discussing SBF clearances not remote controlled plane pistons without rings at .0005" or 6" diameter pistons that might need .013" piston skirt to wall clearance...just trying to not have exception noted...
Thanks...

Strrroker powered... 418 cubes, 518 HP, SEFI, EDIS, Still 20+ forward gears...CB build:http://classicbroncos.com/forums/sho...d.php?t=278607 NWCB Stroker/SEFI/EDIS/4r70W/KluneV/TrueHi9 build: http://northwestclassicbroncos.com/s...n-to-SEFI-EDIS
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Old 02/25/18, 10:02 PM   #60
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Quick ballpark on ring gap, .004" per inch of bore. So a 4" bore should be around .016" gap. .017 would be normal. .020 is a bit much for a normal engine but in line for a boosted application.

Setting the ring in the bore squarely is critical in getting accurate numbers. Eyeballing it isn't accurate. You can use the piston to do so. For the top of the bore use the ring lands on the piston to keep things square. As you get deeper in the bore the piston skirts will keep it square.

At 2500 miles you should see crosshatch with only a few vertical lines in the bores. If it is wore off something is wrong with the cylinders. I don't have enough of the precision measuring tools to check that stuff at home, nor do I plan to have them. Just don't do enough of this work to justify getting them. That is where a trip to a machine shop is needed. Just to figure what is going on.

But given that the bore taper numbers you gave are right, I think you have bore issues. The taper is backwards of normal, usually the top of the bores wear more than the bottom. So I find that odd.

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