73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: jaredts on June 09, 2011, 07:12:55 pm
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I'm doing a cylinder leakdown on my bad cylinder of my 350, and I believe my biggest problem (probably not the only one), is in the exhaust valve of #4. If I push down on the valve it fairly easily drops 1/8" or more before I feel strong spring pressure. I don't really feel it come back up and the leakage is much worse. If I then wack the valve (rocker arm really) with a rubber mallet it seals back up. That's not right, right??? I am sure I'm at or near the top of the compression stroke. I haven't done any other cylinders, but in a compression check a while back this one was the problem. Should I put the valve cover back on and try a seafoam treatment before I go any further?
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Oh yeah, I hear the air escaping out the exhaust, and after pushing down on the valve to get it to leak more its louder at the exhaust pipe. Its getting late, I might do all of the cylinders tomorrow, or at least a couple others for comparison.
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What are you "pushing the valve down" with? You are correct in assuming that this isn't good. Do you have the rocker arm removed? You want to try to isolate the item causing the problem.
At this point I think I would get the piston to TDC & remove the spring. You can use air to hold the valve closed, however I'd use the rope fed in the sparkplug hole in this case. I would want to move the valve up & down to see if there is resistance near fully closed...bent valve maybe? I hate to be thinking negative, but I think purchasing head gaskets is in your near future. Lorne
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Originally I just whacked it lightly with a rubber mallet, and the leakage decreased. Repeated hits with the mallet after that didn't change anything, so I pushed down on the valve with my fingers and the leakage increased. Tap it with the mallet it seals up a little better again. I've had myself convinced that I have bad rings, but haven't yet seen evidence of that with the tester, so pulling the heads and not changing the whole motor would be good news. checked #6 last night and it was good at 20% leakage. I'm not going to tear into this motor at all if I find air coming from the dipstick tube on any cylinders, so I need to test all cylinders.
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I guess my bottom end is good, best I can tell. My head numbers come up as crack prone, poor flow, etc. Now I guess I'm looking for assembled heads that don't require all kinds of other new parts. I'd go vortec but rockers, hardened pushrods, and an intake seems to jack the cost up. Is this the best thing going for a budget oem style replacement?
http://www.summitracing.com/parts/SUM-152123/ (http://www.summitracing.com/parts/SUM-152123/)
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I can't find the link but I think it was Lorne that mentioned some budget minded china heads for sbc that seemed to be pretty comparable.
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You must be talking about the eq heads in this post:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=19333.0 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=19333.0)
I haven't found them at a great price, and would like assembled heads. I'm open to anything at this point. In the past I would just yank the heads and get a valve job, but now this darn internet and all of its info tells me not to mess with smog era heads, and that my casting number is one of the worst (462624). I found a deal on Edelbrock e-street heads for under $800 for the pair, assembled. Still trying to decide. Should I spend $800, $1200, $3000? My head's spinning.
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whats your budget? and whats the goal?
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My goal is to spend little, but have something a little better than crack prone, low flow heads.
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If you can open the valve with your finger there's your issue. If the spring isn't broken you need to pull the head.
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Thanks everyone. I'm guessing its a worn valve guide full of crud, so I got a price on reworking the heads. $160 each but seats and guides are extra and if I have all new seats and guides done it will cost something like $600 for both heads. From what I gather this would be a dumb move as these heads are garbage. Anyone have an opinion on the summit head I posted or know of another way to get this done for under a grand?
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so I pushed down on the valve with my fingers and the leakage increased.
When you find why you can push the valve open with your fingers...you will know the cause of your leakage.
Earlier you mentioned "drops an 1/8" fairly easy before I feel spring pressure". Sounds to me the spring has broken. Look around it to see if Two wraps are laying on top of each other.
A guide full of crud should be HARDER to open by nature, but it CAN'T be easier! That reasoning can't apply if your pushing the valve open with your finger. Lorne
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Hmmm. I looked, but maybe not closely enough. I've got the valve cover back on it now, so it might have to wait a few days to look again. I'm going on the assumption that I didn't miss anything and I need some heads. I'm having fun just looking for now, but what the heck, its only a little more money to get into vortec heads, I might go that route. ??? Heads still spinning a little (lots of options).
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You do know there are 2 springs per valve, right? One inside the other.
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I wouldn't feel too hesitant on using those summit heads. Summit Racing owns Trickflow, so that's probably the company making them. They should make some good low end torque.
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Well, I was going to wait and run a few errands with the truck, but I think I'm going to tear into it tonight. Been several years since I pulled heads, but I think I've got it down. I want to check out the bores before I buy anything. Currently torn between vortec and the summit heads, which I have read are dart s/s castings. One thing I'm a little concerned about with the vortec option is compression ratio. With an old tired bottom end I'd hate to tax it too hard with a big jump in compression, but I'm still considering it. Who knows, maybe my truck won't look or run like a jalopy in the next few months.
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either route will help ya out.. good luck man
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A few hours work and.....
cracked exhaust valve:
(http://i970.photobucket.com/albums/ae188/jaredts/crackedexhaustvalve.jpg)
headless:
(http://i970.photobucket.com/albums/ae188/jaredts/headremoved.jpg)
The cracked valve was sunk pretty deep in its seat compared to the others, but I think they'll all be pretty ugly. Haven't taken the other head off yet, but I'll get it.
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I ordered the Summit heads today. Borrowed a telescoping gage to check the bores hopefully tonight. Threw calipers just on the ridge and got 3.99", so I'm pretty sure they're stock bore size. Checking bores from the top, should I just check them in two directions 1/2" down or so, and then bring that piston to the bottom and check it both ways at the bottom? Anything with the heads off that can be done to evaluate rings? It would be nice to have a dummy plate that I could bolt on in place of the heads and leakdown test it. Should I just wait for the new heads, bolt them on and leakdown test every cylinder before putting everything back together?
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You're going this far why not do it up? This kit with pistons is right around $200 bucks http://www.summitracing.com/parts/SUM-SBCKIT1-000/?rtype=10
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usually pistons with an oversize bore have them stamped on top, so if there is no stamp, then pretty sure its standard bore, which seconds your measurements.
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Those are stock pistons. Id know, i have them. You have a cracked valve, i have a cracked head. And strangely enough, my pistons are in the same position as yours....
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The cylinders look like its got some miles on it, but no score marks and the size checks good everywhere I checked. I'm willing to take a little risk as I didn't want to pull this motor at my house, I need to take it somewhere else if I'm going that far (no garage, no hoist, no stand). If I could do the bottom end with the block in the truck I'd go for it. I saw your post, '79c20, and it is kinda funny. Your symptoms were pretty close to mine. I halfway expected to have air coming out an adjacent cylinder when I did my leakdown test after seeing your post. My best price for rebuilding my heads was $450, so I just spent $630 on new, better heads (shipping included).
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Just clicked on the link, Vile. Out of curiosity why would you buy a kit with new 4.0" pistons if the old ones aren't damaged? If you are only honing the cylinders wouldn't you just rering with the old pistons?
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Heads just delivered, less than 24 hours after I ordered them! Shipped out of Ohio, which isn't far from my house.
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Because they're hypereutectic and flat tops. Yours are dished cast pistons. Why wouldn't you replace them? To save $80 bucks having them hung on the rods? I'd definitely go that route.
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That makes sense. I really wish I had the place to pull the engine and go through it. It almost looks like there's room to hone it right where it sits.
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Where there's a will there's a way ;D
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I played it out in my head, and although it might be possible to rering in the truck certain steps don't sound like fun, and I'm not sure I could get a hone in the back two cylinders. I think I'll put this together and probably won't be 100% pleased with it. It smoked a little before, and even though I didn't detect anything with the bottom end during the leakdown test i'd say It'll still smoke a little--I have a hard time believing it was valve guides/seals. So the plan is to put this together and find a buildable block for a long term solution. Got the new heads painted, the block deck scraped and cleaned and all the bolt holes tapped. Wipe it down one more time tonight and bolt the heads down (unless I have to work late).
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I beat you to the punch! Got to drive my truck last night.
http://boxwrench.net/specs/chevy_sb.htm (http://boxwrench.net/specs/chevy_sb.htm)
this page is very helpful when rebuilding the top end. Make sure you torque your heads in the special sequence. And i torqued them to 30, 50, then the required 65 in the special order. You can even view my page for help if you need it.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=20691.30 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=20691.30)
good luck!
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Hope your truck's doin' better. Mine's not yet. Finally had a break in the weather so I start wiping down my new heads to install them. I look at one of the exhaust valve seats and notice a wide spot on the seat that didn't clean up when it was machined. Its probably only missing the valve by .01" or so, and I don't know how deep it goes, but it doesn't look good to me. I already painted them too.
edit (better pic)
(http://i970.photobucket.com/albums/ae188/jaredts/DSC03903.jpg)
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Jared, If your referring to the top valve where it is almost touching the other one...It's not a problem from what I think I'm seeing. The small Gray band right beside the valve is the seat, under the valve head is where it seals. The rough cast area that is machined most of the way around is just what was left from the work being done. If this is what your concerned with, it isn't a problem...if there is more than what I see, please explain & we'll try to help. Lorne
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The circled area is non-cleanup on the machined valve seat. It extends some unknown distance under the valve. If I had a .005" or .010" pin gage I could push it under the valve all along this area.
(http://i970.photobucket.com/albums/ae188/jaredts/markeduphead.jpg)
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That's the cut not the seat. Use layout dye or lapping compound to see the contact pattern. Or put aq sprk plug in, fill the chamber with ATF and see if it leaks out over night.
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I see the area...The Gray 1/16" area around the valve is the replacement seat. The "chipped away" looking area in the center of your circle isn't hurting anything if that is what your looking at. To be sure, you can test it with a hand-held vacuum pump & a plate easy enough.
Sorry if I'm not following you, maybe it's not really what I'm making of it in the picture. Lorne
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This is a brand new head, so I'm not sure what you mean by replacement seat. Is there a hardened seat insert further under the the valve that I am not seeing? I thought the valve should be supported/sealed all the way out to its outside diameter? If I check the valve for sealing with atf or vacuum pump it may pass, but only be sealing on a fraction of what it is supposed to leading to early failure?
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It either seals or it doesn't. The contact pattern you will see is typically very narrow and on an interference angle.
(http://www.scooterinvasion.net/pics/brokenscooterparts/brokenscooterparts171.JPG)
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I sent pictures to Summit and they replaced the head. Got it started today and it seemed to be running great for about five minutes. Then it died suddenly...no spark. Valves are moving, so its not the timing chain. Getting ready to go back out and try to figure this out. I'm assuming pickup coil or ignition control module? I checked for voltage at the dist. power wire and its there.
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Could be coil too, but suddenly losing spark, probably ICM or pickup coil.
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Ignition control module tested bad at the parts store. Threw in the new one and it started right up. Set the timing, checked for leaks, so far everything seems to be good. I drove it around the block and oh baby does it drive nice now. I fixed about a dozen other problems while I was at it too and also got rid of my ac compressor. Man that thing was in the way.
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Nice! Got any pictures? Have you noticed a gain in power?
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Did you test the new module at the parts store? What brand? I've had some borg warners that couldn't make it off the shelf good, the only one in the store that DIDN'T fail out of the box was an accel.
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I can post some pictures, but its not buttoned up very well. Difference in power? My truck was dyin a slow death down the road. It really runs and idles well now. Pulls stronger than anything I've had, but I've had pretty much stock small blocks to this point. I don't remember what brand ICM I bought. The truck doesn't smoke anymore either, with a little exception. When I stomp it in park it blows a tiny puff of black smoke (unburnt fuel). I'm not sure at this point whether I should go back over my valves with it running or not, I used eoic method before I put it together and I'm not sure if I have the magic touch or not. I think I detect a little bit of clatter of loose rocker arms, but not sure (not loud at all).