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jbeary

Engine issue questions, honest opinions appreciated

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The 3.8 supercharged planned build has hit a major issue. I broke off a tap in a timing cover bolt hole so the block from the 93 pull a part engine is kaplewy. I spoke with the machinist who did the heads and crank and he agrees that I just as well get another block. In the mean time I diagonosed the 89 with bad compression rings in the #5 cylinder and since I already have most of the parts together to do a rebuild, I decided to start on rebuilding the 89 engine figuring I could do it on the cheap.

Well, as fate would have it, I broke two head bolts, one in each side. Sure enough, #5 cylinder does not look like it's had compression for a long time. Heads are in surprisingly good condition as are the internals. Guess the guy I bought it from wasn't lying when he said the engine and trannie were rebuilt about 50k miles ago. Probably not the original engine or transmission from what I can tell at this point.

Here's my quandry, what's the chances the compression rings in one cylinder weren't gapped correctly, or weren't clocked correctly? Like the idiot who probably did the rebuild work, I didn't write down the readings and I didn't do a leak down test on any cylinder but #5. From what I remember, all of them were close and #5 was obviously whacked. Top view of the piston looks okay. Bore isn't scored and measures round, seemingly so with a harbor freight mic. Yet oil rings do not leak. I don't know any other tests I can do without pulling the piston. I put a new compression ring in the bore and squared it with a different piston, ran a feeler around the circumference so I am assuming it's really round and does not require boring. Other than pouring oil in the cylinder are there any other tests suggested?

How impractical is it to think I can just hone the bores, slap in a new set of rings and bearings and be on my way with this? I already have a freshly turned crank, a full set of new rings, bearings and gaskets and from the looks of the valves, I'm sure I can save my fresh set of heads for the supercharged build. I would still replace the guide seals and lap the valves and seats but I don't want to use my new heads nor do I want to use my SC pistons/rods. I believe the 89 and the 93 cranks are the same.

Anyone think it's completely ridiculous to replace only the rings on #5 without honing? Lots of trouble, pulling the engine and risk tapping out two major bolts, to just pull one piston for a set of rings. I want to put a minimal amount of machine work into this. Meaning, I've been having thoughts of parting out this car only so I don't have to obtain yet another $300 block. Need a car and don't want to beat the 91 but that's what I'm doing the more I drive it with a busted front suspension. Really would rather the shop tap out the head bolts without having to drop the crank, but I can imagine that conversation already. Would lead to new cam and balance shaft bearings at least and I don't want to spend the dinero (I just don't have) at this juncture.

What can I do to just get by??? Need some good news folks. Please tell me I can just drop in new rod and main bearings, hone the bores, slap on new rings, lap the valves and have something that may last another 50k.

Thanks to all in advance.

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I rebuilt my sisters series 2 3800 in a monte carlo - at that time had the crank turned and fluxed then the machinist asked where the rods were . I am puzzled , so he begins to tell me that the 3800 rods were "out of round prone" with normal driving (to check them while out or the bearing will not fit when installing and have to take motor back apart ) . I had 2 of them out of round - they exchanged them out for 2 others . I also did just a hone to the block and installed new rings to original pistons .This motor has 4 years and over 20,000 miles on it now . good luck

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I will take a shot at this.

First of all, your block with the tap broken off in it is salvageable unless you really did a number on it. Get a high speed die grinder with a 1/8th collet. Go to Handy Dan or comparable place and find the Dremel bits. You need a carbide cutter with fluted straight sides and rounded on the end also with flutes. That bit will cut nearly anything and should be small enough to work on that tap. If you can get in the flute cavity and cut it into pieces you may get it out.

If you grind straight in and cut out some threads, it will not substantially weaken the bolts clamping ability. When you get the tap out you can helicoil the hole if you like. I recommend you buy at least 2 bits as you will break one if you are new to this operation. I have successfully salvaged many heads that had exhaust bolts broken off this way. If you used a carbide tap, that could be a problem. High speed steel is somewhat softer. Those dremel bits are around 8-$10 apiece.

Secondly, if that #5 cylinder had no compression but looks ok, have another look at the valves. Pour some thin liquid in each port and physically check them for leakage or warpage. As for pushing that piston out, why not? New rings will seat in a good cylinder but a light honing would be preferable. You will know if you have a problem with the rings when you push it out, but you still have an issue with 2 head bolts to get out. That is a drilling job and get dead center and sized for a big eazyout. You will still have to soak it to get it to turn. An alternate method would be to super heat it and it might loosen. If the top is exposed above deck level, you can weld a big nut to it for leverage.

I like the idea of salvaging the first block if possible. Remove head bolts from second block as a back up if the valves are bad in #5.

Good luck.

Edited by TexasJohn55 (see edit history)

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After further consideration of your broken tap issue, I have seen them broken up and dug out in pieces but that also is a hit or miss deal. I assume those are small bolts around 5/16" size, that makes it more difficult as well. I have seen bolts removed from holes with a small tipped cutting torch but I never was that proficient at it. The idea is to heat it very quickly to the melting point and then blow it out in a molten state. The trick is to heat it very quickly while the block is cold and acts as a heat sink and does little damage to the cast iron. Again, the small size makes that difficult unless you have a very small cutting head.

If you find a bit or cutter that will cut the tap material, bore dead center of the tap body and remove enough material that the flutes can be broken off. But oh yeah, you already said the block was "kaplewy" didn't you?

I am surprised someone else has not chimed in with ideas on the 2 engines.

Edited by TexasJohn55 (see edit history)

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A tap is made of some of the hardest tool steel you will find. You will have a hard time finding another tool that will cut it. If you can find a machine shop with an EDM machine large enough they can remove the tap without doing much damage to the block. Once the tap is removed you can install a Heli-coil to fix the threads if needed.

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I saw an article on the EDM removal of broken parts somewhere also, and would seem to be a good solution other than cost and shipping if required. It would be a shame to trash an otherwise good block for a couple of buggered holes, but the cost to repair may be prohibitive. I would think a good machine shop would know of a reasonable solution since they likely run into this often.

I saw the comment about rods being out of round, assuming the big end, but I haven't seen evidence of this on the few 3800's I have had apart. Maybe outside my ability to measure? This is a relatively low rpm engine so I would think stresses would be low?

Relative to the bad cylinder, a bottle brush hone and re-ring for a single cylinder for a quick fix, okay, but if the cylinder appears to be out of operation for an extended period, I would look elsewhere. It would have to be pretty bad ring seal to not run at all. Bad valve seating, maybe sticking, or possibly a rocker arm issue might lead to poor compression, or possible headgasket? Dead cylinder for other reasons would be injector or spark.

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Years ago, I rebuilt (a mistake) a '86 3800 that had a SEVERE rod knock. Guy ran it til it didn't run anymore, and junked the car ('86 Park Ave).

Upon disassembly

, it was known the crank was junk, but three rods were so out of round as to be egg shaped. You could SEE they were out of round.

Amazing it ran...

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The best way to measure the rod for out of round it to take it to an automotive machine shop. You can do it with a inside micrometer, that most people don't have, or a snap gauge and outside micrometer but it is too hard to consistently measure down to 0.0001 that way.

Sunnen rod honing machines that resize the rod has a fixture with a dial indicator for measuring the rod. That makes it a 15-20 minute job to accurately check all the rods for correct size and out of round. You can save the machine shop some time by having the rods cleaned and the bolts torqued to the proper spec ahead of time. When I use to do it the cost was $2 per rod to check and $8 per rod to resize if needed. You can probably double that cost now.

Resizing consists of grinding the cap and rod mating surface (with a special fixture) to make the rod undersize and slightly egg shaped. Then the rod is honed out to the proper size with a honing machine made for that purpose.

Having the rods checked is money well spent if you are rebuilding an engine. The same is true for having the crank checked and polished.

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Thanks guys. I feel a lot better after your input. The FSM is both clear and vague in section in 6A5E-28. And there's two schools of thought, the DIY or pro machinist will always tell you a definite bottom rebuild is required if a piston needs to come out. That includes a bore and hone and all new bearings as well as a freshly ground crank. Most also insist on new lifters and push rods and I honestly think that may be were these guys lose me. The second school of thought is from the dealer service perspective that says only fix what's broken. Which means leave the heads on, pull the piston from the bottom, and reuse all bearings, just replacing any broken rings with a light hone on the cylinder, measure clearance, and generally reassemble with all used parts but new gaskets. I haven't had much luck with dealer repairs and I always err on the side of caution so logically, a full bottom rebuild sounds more reasonable.

I just did't want to get that far into the 89 engine, thinking all along I would eventually junk the car after getting the 91 where I want it. Still swapping parts and using the 89 as a daily driver. Had a couple of days to myself before gall bladder surgery, so I got the 89 stripped down. My dad came over the Sunday before my surgery and we looked at the broken head bolts and agreed the engine probably needed to come out. Wasn't much work to get it there so I can now just pull it. IMHO dropping the starter and unbolting the AC compressor is easier than laying under the car with crap fallin in my eyes. Torque converter bolts were nothing to remove and it's easier to break the balancer bolt using the starter method while it's still in the car. Not a big deal at all.

Pulling the the engine makes me want to visit the machine shop, but I ain't got the dough to "make this right" like my machinist always tells me. Want to do a quick and dirty on this engine but those head bolts messed up that idea. I have a junker head in case the one on #5 was cracked or warped. That does not seem to be the case on the original heads. Valves are not burnt, and I did the petrol test on each to verify they were not leaking. The heads from the 93 Bonneville were trashed by comparison. That and when I did the compression test, I had good results from all cylinders except for #5. Wet test indicated bad rings, and I garauntee you there was a strong indication of blow by when air was applied to that cylinder. I didn't do that test on any other cylinder but didn't think about it until I had the heads off. The others had good compression anyway. Pretty sure I did a good diagnosis before the tear down, just wish I would have written down the numbers.

Didn't have any issues with a knock on the 89 so I'm assuming the bearings, rods and crank are okay. I was going to get an auto zone loan a tool hone and leave in the crank and do a light hone. All cylinders are well within tolerance according to the HF mic I have. Some Harbor Freight stuff is junk, I know, but this thing seems okay. I did get a better torque wrench and Impact wrench from Lowes. Some of Lowes Kobalt brand stuff is very good and while I spung for a very nice cordless Craftsman impact, angle grinder, and reciprocating saw kit, the Sears branded tools just aren't that great any more.

Heres es some pics showing the engine in the 89. 2&3 are compression and exhaust stroke. 4&5 are TDC on #5 and #2 showing full travel, #7 shows lifter position so the cam is probably just fine.

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These are pics of the buggered up timing cover hole. You can clearly see the tap (HF JUNK) and where I tried to drill around the flutes. I stopped because I was afraid of breaking off a "good" carbine bit, but the thing is actually kind of loose. Machine shop estimated $150 to remove, weld and retap which is why my machinist said to just get another block. I still would rather not plunk down yet another $300, then the labor of tear down etc. Its a timing cover bolt for Christ sakes. I could probably leave it and still be okay. Time needs to go into getting the 89 back on the road and I thank you all again for the input. I think I'm going to pull the block from the 89, weld on some nuts to those broken head bolts, and if they come out, I'll just pull #5 hone the cylinder with the crank in as planned and hope for the best after reassembly.

Will also try Texas John's advice on the carbine dremel bit. If I can get something past one of the flutes, I think this will turn enough to lift out. No way this will drill, like Ronnie said, it's harder than the carbine bits I have. You can see how scored the edge of the hole is from me trying to drill at it sideways. Moral of this story is to avoid cheap ass HF taps. Get a good set of taps and never ever put sideways pressure on a tap even if it's not that deep or tight. That's exactly what got me into trouble with this one. Tap has to be dead straight. They don't flex like drill bits.

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J,

They make a tap extractor tool which may or may not work in your case. The tool comes in three and four flue for different diameter/thread taps.

Here's a link to Amazon showing what these tools look like.

They work if the tap is just broken off in the hole, not so much if the tap's threads are jammed in the metal.

The worst that could happen if you choose this route is that you'll break off the tines in the hole with the tap but, you may get lucky and you'll get it out and save yourself a few hundred bux. If you do it, flood the hole with PB Blaster or similar, insert the tool an work it back and forth before trying to unscrew the tap. It will either come out or break the tines off. Good Luck.

John F.

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