Author Topic: What to do about a wrist pin  (Read 16212 times)

Offline Monkey Uncle

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What to do about a wrist pin
« on: February 28, 2017, 08:19:02 PM »
Sorry this post is probably going to be long, but I want to be sure I don't leave out anything important.

Bought my truck a couple of months ago from a guy who assembled it from various donor vehicles.

'85 C 10 body
'78 GMC chassis, axles, and engine; 350 V8, 4WD
turbo 350 automatic transmission of unknown year

Was told the engine had 124k and the transmission had 78k, but no documentation. 

Ran well upon test drive, though I noticed a not-too-loud ticking noise.  Rapid, regular, and correlated with RPMs.  Seller dismissed it as "probably a lifter," although it sounded like it was coming from down low and toward the rear of the engine.  The price was good and the truck otherwise appeared to be in great shape, so I took a chance.  I wasn't looking for a show truck, but rather an inexpensive old truck for local hauling, probably 1,000 mi/yr or less.  I figured even if I had to replace the entire drive train, I'd come out better than buying something newer.  The fact that it could pass for a "20-footer" was just a bonus.  Dickered down to 5 grand and drove it home.  The 75 mi trip home was uneventful.

Recently I decided I wasn't comfortable just ignoring the ticking noise, so I did a little googling.  Based on various old forum posts and youtube's best minds, I figured I had some sort of issue with the flex plate or torque converter (based on the apparent location of the noise).  Took it to my favorite mechanic for cheap old cars.  I trust him because he has a good reputation in a small town where everyone knows everyone, and because he's done work for me before for very reasonable prices.  His first instinct was collapsed lifter.  I was skeptical given where the sound seemed to be coming from, but I figured since he's worked on cars 6 days a week for 25 years, I'd defer to his opinion and let him have a crack at it.

It took him a while to finally get around to taking a serious look at it.  I called him today and asked him what was up.  He said, "bad news, it's a wrist pin."  Says he listened with a stethoscope and could tell that the sound is moving up and down.  He doesn't do internal engine work, but said he could quote me a price on a new crate engine if I wanted to go that route.  He mentioned another guy across town who might be willing to tackle fixing the old engine, but he noted that he doesn't really know of anyone else locally who does major internal work.

So, choices seem to be:

1.  See if I can find someone to confirm that it is indeed a wrist pin, and tackle the repair.  If I go this route, would it make sense to just go ahead and do a re-build?  Seems kind of silly to pull a 40 year old engine and tear it down just to replace one part.

2.  Take Mr. Mechanic up on the crate engine option.

3.  See if I can find a used engine and see if Mr. Mechanic would do the swap for me.  Not sure of my odds of finding a used small block V8 that isn't just as worn out as the current one.

4.  What if I just keep driving it?  I presume if it really is a wrist pin, it will break eventually and the engine will lock up.  Then I have to invoke option 2 or 3, plus a tow and the inconvenience of getting stranded somewhere (with my luck, probably in the middle of the woods somewhere with a full load of firewood).

As you can probably tell if you've stuck with me this long, I'm not really up to tackling the job myself.  Although I understand basic anatomy and function, I don't have the experience, tools, shop facility, or time to tear down or swap an engine.

But on the bright side, labor rates are relatively cheap in this area, with independent shops running about 50 bucks an hour.

Well, that's about all I can think of at this point.  Any help is greatly appreciated.


Offline fitz

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Re: What to do about a wrist pin
« Reply #1 on: March 01, 2017, 04:13:00 AM »
  If you were swapping the motors yourself, I would roll the dice on a $350-$500 used motor off Craigslist.  My opinion is that if you are paying for the labor (as you plan to) I would go with a crate/rebuilt motor.  You don't want to pay the mechanic twice if the cheap used motor doesn't work out.
  You can buy the GM Goodwrench 350/260 HP motor for around $1500.  A few guys on here run that motor and are happy with it.
« Last Edit: March 01, 2017, 04:23:19 AM by fitz »

Offline njschmidt

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Re: What to do about a wrist pin
« Reply #2 on: March 01, 2017, 08:26:10 AM »
I'm sure you probably looked into it already but I've heard a similar clicking sound from a cracked exhaust manifold. There are some YouTube videos where you can hear the sound and that demonstrate an easy fix with furnace cement. Good luck!
1978 Chevy Cheyenne, v8 350 4bbl 5.7L

Offline 82silverado

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Re: What to do about a wrist pin
« Reply #3 on: March 01, 2017, 09:04:43 AM »
Never heard of anyone making a positive diagnosis of a wrist pin with a stethoscope.
82 Silverado 454/700R4
86 Buick GN
02 WS6

Offline VileZambonie

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Re: What to do about a wrist pin
« Reply #4 on: March 01, 2017, 10:34:34 AM »
If you've eliminated the flexplate as the culprit and in fact are hearing a sharp knock you can waste time trying to determine which cylinder it is or if it's mains but regardless the engine needs to be rebuilt or replaced. Where do you live that $50/hour is the labor charge? If it's that cheap a new engine won't cost you much to have installed.
,                           ___ 
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline Monkey Uncle

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Re: What to do about a wrist pin
« Reply #5 on: March 01, 2017, 01:57:28 PM »
I'm sure you probably looked into it already but I've heard a similar clicking sound from a cracked exhaust manifold. There are some YouTube videos where you can hear the sound and that demonstrate an easy fix with furnace cement. Good luck!

Yeah, I'm pretty sure it isn't an exhaust leak.  I've had those before with my previous truck and am familiar with what they sound like.  It's hard to describe in words, but the sound quality is different.  The current noise has a sharp, hard tapping quality to it.

Offline Monkey Uncle

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Re: What to do about a wrist pin
« Reply #6 on: March 01, 2017, 02:00:34 PM »
Never heard of anyone making a positive diagnosis of a wrist pin with a stethoscope.

I don't know that he was 100% certain, but that was his conclusion based on the fact that he said he could hear the sound moving up and down within the engine block.  I wasn't there when he listened with the scope, so I can't vouch for the validity of the conclusion.

Offline Monkey Uncle

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Re: What to do about a wrist pin
« Reply #7 on: March 01, 2017, 02:03:44 PM »
If you've eliminated the flexplate as the culprit and in fact are hearing a sharp knock you can waste time trying to determine which cylinder it is or if it's mains but regardless the engine needs to be rebuilt or replaced. Where do you live that $50/hour is the labor charge? If it's that cheap a new engine won't cost you much to have installed.

Rural WV.  You certainly won't get $50/hr at a dealership, but it's possible to find small independent shops that will work for that price.

Offline 82silverado

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Re: What to do about a wrist pin
« Reply #8 on: March 01, 2017, 02:34:51 PM »
Good luck with that.
82 Silverado 454/700R4
86 Buick GN
02 WS6

Offline Stewart G Griffin

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Re: What to do about a wrist pin
« Reply #9 on: March 01, 2017, 07:32:12 PM »
1)The engine is actually 39 years old, not 40.  :)

2) Is the engine otherwise smoking and/or using oil and/or using coolant?

Offline Monkey Uncle

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Re: What to do about a wrist pin
« Reply #10 on: March 01, 2017, 07:54:14 PM »
1)The engine is actually 39 years old, not 40.  :)

2) Is the engine otherwise smoking and/or using oil and/or using coolant?

It smokes just a little on startup, but not while running or idling.  No drop in the oil level, despite a small leak somewhere near the back of the engine.  But I haven't put many miles on it, couple hundred at most.

No drop in coolant level.

Offline Monkey Uncle

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Re: What to do about a wrist pin
« Reply #11 on: March 04, 2017, 12:55:46 PM »
Just tried the spark plug wire test.  Several random people on the internet say that a wrist pin will stop making noise if you cut the power to the affected cylinder.  So I pulled the spark plug wires one by one to see if the noise would go away.  I went through all 8 cylinders twice, but the noise never went away.  It varied a little in intensity over the course of the test, but it does that anyway as the engine warms up.  And the intensity never made an obvious, consistent change with any particular cylinder.

This makes me think the noise is not coming from the inside of a cylinder.  But I don't really know what I'm doing; what do you think?

And just as an aside, I could hear a clacking noise coming from the top end whenever I had a wire loose.  It would immediately go away as soon as I reconnected the wire.  I presume something is going on with the valves or lifters whenever a cylinder loses power?  Not that it has any bearing on the real problem; I just thought it was odd.



Offline 82silverado

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Re: What to do about a wrist pin
« Reply #12 on: March 04, 2017, 02:38:11 PM »
Tearing it down is the only way to know exactly what it is. Speculating is virtually a waste of time.
82 Silverado 454/700R4
86 Buick GN
02 WS6

Offline Stewart G Griffin

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Re: What to do about a wrist pin
« Reply #13 on: March 04, 2017, 08:28:25 PM »
Do you have AAA?

Offline Monkey Uncle

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Re: What to do about a wrist pin
« Reply #14 on: March 05, 2017, 05:36:31 AM »
Do you have AAA?

No.  Are you suggesting just continuing to drive it until it blows?