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-   1987-1991 (https://www.gmforum.com/1987-1991-93/)
-   -   3.8L Rod Knock (https://www.gmforum.com/1987-1991-93/3-8l-rod-knock-281962/)

mics89 06-10-2009 12:21 AM

3.8L Rod Knock
 
I recently purchased an 89 LE from my friend's 83 year old Mother. She owned it for many years and always had it serviced and kept up. The interior is immaculate. She only drove it about 5 miles a day for years. One day she let her young grandson borrow the car and when he brought it back. It was making a motor noise.
My friend brought it down to my shop and we determined that it had a light rod knock. A week later the noise got a little louder and she did not want to trust the car anymore or put the money into it to fix it, so that's when I bought it.

My plans were to just run it until it seized up or until my truck restoration was finished. As time went by and I drove the car more. I began to fall in love with it. Now I want to fix the car and replace or rebuild the 3.8L. I have the crank case filled with products such as Lucas,STP and Slick50 to slow down the destruction as much as possible until I figure out which way to fix it.

The car has 151,000 miles. The motor runs great except for the knock.

Should I ......
just do a crank kit replacement?
Or rebuild the whole motor?

I would also appreciate very much any information on the cheapest parts for the work I need to do. I found a crank kit on Ebay for $99, so that's not to bad. Engine Master rebuild kits I found for around $850.

Thank you for your time for reading about my sick car:)

Purplehazeir 06-10-2009 01:06 AM

How did you determine it was a piston rod and not a push rod/lifter noise?

BillBoost37 06-10-2009 07:39 AM

I would have started out the same way. As you know the only down side to seizing is fighting for the TC bolts if a swap is planned.

I'd look around for a replacement motor, which is probably getting tough to find. After that..I'd slap that crank kit in. The rings etc on these motors are not a high wear item. You would probably have the least amount of work if you pulled, rolled it over, crank slapped it and dropped it back in. IIRC a crank kit comes with crank and all the bearings. As long as none of yours are seriously trashed...it would be crank slap time for $100

mics89 06-12-2009 03:06 PM

Quote:

Originally Posted by Purplehazeir (Post 1380285)
How did you determine it was a piston rod and not a push rod/lifter noise?

I did some research on the 3.8 motor because, actually I work on old classic cars,mostly Fords and I don't know the 3.8 all that well. I searched out the most common failures for the motor that are listed on google.
Push rods, lifters as you have spoken of. Crank shaft and piston wrist pins. Harmonic balancers and belt tensioners.

I ran down the list.
Check the Harmonic and belt tensioner. I'm glad I did because the harmonic was making a very small noise,but it was not the main "Knock" noise. So I replaced the Harmonic before it got worse. The belt tensioner was already replaced about 30,000 miles ago and still work perfectly. Alt, water pump,steering,etc were fine as well

Next I started toward the harder things..

Took off valve covers,with motor running and inspected the upstairs(push rods,rockers,lifters) then I shut it down and disassembled each to get a closer look for wear. Push rods rolled straight when put on a level/flat surface. Rockers all had the same amount of wear. I used a small light/telescope to peek down on the lifters and everything was clean,no dirt/gunk. No unusual markings.

Then I put everything back together(in order), and started to think about the bottom end more,now that I inspected all the other common suspects.

If it's a wrist pin,then a crank kit won't do much good, I would need to get a Master rebuild kit instead,because I would want to replace everything. Timing chain,cam,lifters,etc along with the new pistons and wrist pins.

Crank or wrist pin,now to determine that. I must get inside,so I've done more research for used motors in my area and have found 6 of them ranging from $350 to $1200.
But I'm Always weary on junk yard motors. I havent found any engines that are still in the car so I can hear it, I just have to go by the Junk Man's word.

That maybe the road I will have go, just buy a cheap motor,than I can have time to tear down the original. This may seem like lots of work to most people and especially for a car that is only worth $1400 book value. But I'm a certified motorhead and this is Fun to me:) I love all automobiles and it keeps my mind fresh to learn new things.

In the near future I'm also hoping to add a "Smacks" Hydro booster to it. I got the plans from smacks boosters site and built it myself. I love to tinker.

Thank you for your responses. I'm on allot of forums for many different types of automobiles and this is one of my favorites. There are so many "Good" catergories.


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