3400 head gasket destruction

[AaronGTR]

Well I dropped the engine off at the machine shop today. This is where I took it. http://www.enginelaboftampa.com/index.html They have a good reputation locally and seem to do good work and have a really nice shop. A little more expensive than some, but I'd rather have someone working on it that knows what they are doing.

They have worked on a few 3.4's before, and said they have found problems with the cam bore not always being straight. They said that might be a problem with mine and might have had something to do with the oil pump drive wearing out and the cam bearings going bad. They are going to tear down the rotating assembly and tell me what they find, and if the cam bore is off I am going to have them align hone it and put in over size cam bearings. Since the entire rotating assembly will be apart I may have them balance everything too. Depends on if I get the money in soon that I am waiting for. They charge about an extra $370 for that, but they said I could rev to 7000rpm and could gain up to 10% HP just from that, and it would have better longevity and possibly less strain on the timing chain and valve train. So I'm thinking about it.

I decided to keep the LS6 valve springs, and I will probably have them machine the spring seats on the heads so I can install them at 1.8" and drop the seat pressure just a touch and gain some available lift for future use. I also ordered the LS lifter springs and a 3500 valve set from Ben, and will have them do a valve job with those once I get them here. I already have a new oil pump drive and timing chain on the way, but I'm thinking about whether I should get the 96-99 timing set or not. Even with the stock cam, I'm not sure if the stiffness of the LS6 springs would still stretch the chain out or not. The one I took off wasn't too bad but only had 12k miles on it. I still have a set of stock length stiffer pushrods from Smith Bros so I'm not worried about pushrod deflection.

[AaronGTR]

More bad news. Heard back from the engine shop today. #2 rod was bad, so I'll definitely need a new one of those. Was kind of expecting that though, and at least it wasn't the crank or something. The really bad news though... the piston diameter is worn down below tolerance and the cylinder walls (while still smooth) are worn above tolerance. All added up, my piston to wall clearance is double what it should be (according to what they told me).

They are recommending an over-bore and new pistons. Otherwise I'll have problems with blow-by and burning oil. Boring and honing the block will only cost $240, but the problem is finding affordable over-size replacement pistons. I don't have the money or the time to wait for custom forged pistons to get made. This whole ordeal is turning out to be way more expensive than I was planning.
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[trotterlg]

There is a set of .040 over coated skirt 3.4 pistons on Ebay now for $120 or so, that is where I got my iron head set for the 3.1 engine I built. You can find some good deals. Larry

[AaronGTR]

if they are iron head and not 3400 pistons though I can't use them. I don't want to up the compression since I'm running a supercharger. I did find that sealed power has oversize pistons for $30 ea. so I'll probably be getting a set of those.

I also thought about swapping in a 3500 instead, but with the price of them locally and the parts I'd still need to get, it would end up being just as expensive.

[bszopi]

If you want it to be your daily for right now, I'd just find a 3400 and swap it in. Get you back on the road cheaply. Worry about the existing block later.

[AaronGTR]

That's the problem though. A used engine around here will cost me as much as the machine work and parts to get the engine I have running. The used 3400's listed for FL are even more than 3500's... $750+ for a running motor, and the rest are just parts or say they are bad motors. And I'm moving into an apartment and won't have a garage to work on the car or anywhere to store an engine block. If I don't use it, it's going to the scrap yard. I'm really just looking to get it running again, still with a decent amount of power so it will be a fun daily, but nothing crazy so that it will still run for a long time. Really, it was running great before the head gaskets blew. Then I just found all these other "ticking time bomb" problems.

[trotterlg]

If you find a set of new std size pistons you will probably get back close to wear limits if the bores are OK, that would save you about $200.00. What cars have the aluminum head pistons in them, I ended up paying $55.00 for a set of 3.1 pistons pins and rings, and they are the coated skirt variety, so you can find some deals if you know what to search for. If the engine was running well with the old pistons in it things can only get better. Larry

[SappySE107]

http://cgi.ebay.com/ebaymotors/GM-3-4-TRANSPORT-MONTANA-SILHOUETTE-PISTONS-599710-020-_W0QQcmdZViewItemQQhashZitem5643a09812QQitemZ370501785618QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

[AaronGTR]

http://cgi.ebay.com/ebaymotors/GM-3-...Q5fAccessories

I'm assuming those are stock replacements? Where would I find the rings for them? I found some sealed power over size ones and they were $173 and $178 for .02 and .04 overbore pistons. Shop would charge $334 for pistons, and more for all the bearings and stuff as well, but they said they would install whatever I want if I bring them my own parts.

They said the heads are flat and holding vacuum, so I actually don't need to do anything on them if I don't want to. They won't just do a simple valve job on them for the 3500 valves though. They'll only do a complete head service (which includes the valve job and reassembly) for $302 for the pair, and an extra $142 to get the spring pockets machined so my LS6 springs would sit at 1.8" installed. It's all adding up way too fast.

The biggest hit is the block assembly. They won't just reassemble the rotating assembly in the block for me, which is the part I've never done and don't have all the tools I'd need for. They want $427 for a long block assembly, and $73 just to take the pistons off and put the new ones on the rod.

At this point it's looking like my cheapest option would be to have them bore and hone the block and replace the cam bearings, then get all the parts myself and just have them press in the wrist pins, and put the rest together myself. I'm just worried about messing it up. I have a factory manual, but I've never assembled a short block before.

Oh yeah, he showed me the measurements they took. Basically the max piston to wall clearance is supposed to be .0027" and right now with the piston and bore wear I'm at .003". The piston bores aren't perfectly straight either, they vary at the top and bottom by a vew thousandths which is why they recommended the over bore rather than just putting new stock pistons in because I would still be on the high side of clearance.

[trotterlg]

If you put in new standard pistons you will probably be within wear limits, not perfect, but it will also cost you $200.00 less to do it that way. Here are some standard pistons, same price, probably get you another 75,000 miles on that engine. Larry

http://cgi.ebay.com/ebaymotors/GM-3-...item56431fe006

[AaronGTR]

Ok, it's been a while since any updates. I finally have the money to order all the parts I need now though, so the machine shop can get started.

The one rod was bent so I ordered a new one off Ebay. Those pistons on Ebay had the 3mm oil ring though, and I couldn't find rings for them anywhere. The rings they are selling on ebay have the 4mm oil ring and are plasma-moly coated and same specs as the sealed power pistons, so that's what I got. I ordered .04 over sealed power pistons, clevite tri-metal rod and main bearings, and a new rear main seal from rock auto. The rings on rock auto where $121 though so I got these off ebay for $47. perfect circle rings

So the only thing I really need now are the cam bearings, and some new head alignment dowels (my old ones are kind of messed up). I'm going to have them do the valve job and install the 3500 valves I bought from Ben, and machine the spring seats down a little to reduce the seat and peak pressures from the LS6 valve springs. I figure with the stock cam specs that should lower the total spring pressures enough to keep the stress down on the stock rockers etc, while still being stiff enough vs stock to not get any valve float.

Even still, I've heard that higher spring pressures can be hard on the stock cam bearings, and the stock cam itself is weak and I've heard of them breaking. I'm debating getting the teflon coated SBC cam bearings for extra insurance, and maybe the solid core sealed power cam as well. That way I shouldn't have to worry about either of those failing (just for piece of mind), plus in the future I should be able to take that cam out and get it reground if I want right? Any thoughts on this? I found this part number for the cam online (CS-1569) and they have it on summit racing. Compatibility is listed for most 94-99 3.1 and 3.4 engines, but the only difference is the cam timing ring and we know that it works with any year sensor, so this should be the right cam to use right?

Only other thing I'm debating getting is the crank scrapper. Would be easy to put in now since the engine's already out of the car, and would be a nice investment for only $58. Shouldn't affect reliability at all. Only thing is I can't find any info on whether it's a drop in install for the 3400 or not. Ben said something about using a 3500 oil pan or something? I don't want to start buying a whole bunch more parts to make it work though. If it only needs a small modification or something I might do that. Anyone know anything about this?

edit: oh yeah, one more thing. Since I'm boring the block 1mm over I decided not to use stock size head gaskets. I still have a set of 3400/3500 MLS gaskets I bought from Ben. They were part of a group buy back in '07 when he had the old 60v6.com store. They are 1mm larger bore size than my stock gaskets, so they would have 1.5mm clearance all the way around same as stock, so they should work fine right? I already checked with the shop about the 50RA or finer surface finish needed to use them, and they said the block and heads are ok for that. Only thing is they don't say what compression thickness they are. Does anyone remember if those were stock .06" thickness? I don't believe comp thickness was an option back when the group buy was done, so I'm pretty sure they are .06 but I want to make sure.

[3400-95-Modified]

I used Bronze on his stage 1 cam...

I'll try to find the pics, but it was only 15k miles and it was close to same as your one side all the way around. No wear so far on the new WOT re-grind cam and the stock gear.

They wear out so fast because they are so soft and as you noted, if floating around in the oil, they wont cause any damage to the other parts.

I'm also not sure what Bronze Ben was able to get when he had these made, maybe it just wasnt up to snuff to deal with the abuse and there may be something stronger... not sure.







That cam also did a job on my cam bearings as well.

[trotterlg]

Looks to me that the front bearing is installed backwards. Larry

[3400-95-Modified]

Looks to me that the front bearing is installed backwards. Larry

Tell that to GM then, that was the factory bearings at 19k miles... 15k of them with the Milzy cam.

Aaron, I have the 3400 crank scraper, it installs nice and shouldnt require any modification, other than double checking for clearance during install on the rods and crank.

Installed pics.








And with the 3400 oil pan... since the 3500 wont even fit a 3400 block anyways.

[AaronGTR]

Excellent. Thank you!

I did go ahead and order the crank scrapper (someone else told me it fit on their engine) but it's still nice to see installed pics. I also went ahead and ordered the solid cam and teflon coated SBC bearings. I'm all moved out into my new apartment now, but I'll be heading back to my friends garage to work on the car some today. Some more parts have arrived, so I should have everything I need now. I ordered a ring grinder yesterday for the assembly when I get the block and pistons back. I already have a set of gauges for checking the ring gap. All I'm waiting for now is the money to pay the machine shop to start the block work.

Only thing I'm wondering about now is the bearing clearances on the crank. My dad said since I'm not getting anything done to the crank or bearing bores or the connecting rods, and I'm using stock size replacement bearings (clevite tri-metal), that I should able to just put the bearings in with assembly lube and torque everything down. Do you guys think I should still check it with plasti-guage though? I've never used it before and don't know what size to get, but I know it's pretty cheap.