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1991 TA LB9 is worn out... now what?

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Old 08-07-2018, 05:26 PM
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1991 TA LB9 is worn out... now what?

Hi there,
I did do a search on this but I didn't find what I was looking for. I have a 1991 Trans Am with LB9 305, automatic, 228K miles on it, and it is worn out. Low compression, smokes, idles rough, etc. So I need to rip it out. I am trying tp decide how to proceed with a replacement:
1. I could rebuild the original (this would be the most work, possibly the most expensive, and not sure of my engine-building skills)
2. I could pick up a free short block 305, there are 2 on CL right now (could be similar problems as option 1)
3. I could buy a 1990 caddy 350 TBI engine and trans for $650 running in car (might be cheapest and easiest)

I am leaning toward option 3, but I have several questions:
Is the 1990 Cadillac engine a roller-cam engine? Would it be compatible with my top end?
If it is a roller, are the TBI 350 heads any good, or would I be better off with my 305 TPI heads?
To swap from 305 to 350, I need a 350 knock sensor, 350 memcal chip, 22# fuel injectors. Anything else I missed?
Assuming it is a roller motor, I was planning on taking the pan off, taking the bearing caps off, and doing a plastigage test to check the bearing wear. If they are okay, I was going to button up the bottom end and leave it alone. Any suggestions?
I am assuming the TBI cam is not the best choice for this build. Any better ones?
Any recommendations on parts to replace? If I take the cam out, should I replace the timing chain set?
If the engine truly does not smoke, should I use the TBI heads? Are the 305 TPI heads better? Should I get them rebuilt?

That's all I can think of for now, but please let me know if there are any gaping holes in my plan.
Thanks
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Old 08-07-2018, 05:48 PM
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Re: 1991 TA LB9 is worn out... now what?

Just ring slap the old motor, and do a top-end rebuild. If it doesn't knock it probably just needs new rings and a valve/head job. Pull the pistons, check bearing condition, and replace the rings with a new cast-iron set. DO NOT hone the cylinders. Just new rings, head work, and run it.

The devil you know, is always better than the devil you don't.

Either that or do it right and get a 350 crate engine and be done with it.

GD
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Old 08-07-2018, 05:51 PM
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Re: 1991 TA LB9 is worn out... now what?

Unless you're really strapped for cash, I'd skip the classifieds used engines. For $2,000 give or take, you can pick up an L05 crate engine (12568758) new from GM. For about the same money, or maybe even a hair less, you can pick up a L31 Vortec 350 crate engine, add a TPI Vortec base and you're miles ahead of the L05. Or for a few hundred less Jegs offers a 350 TBI crate that should bolt right up to the stock TPI. https://www.jegs.com/i/JEGS/059/8758/10002/-1

As you can see there are lots of options for nearly bolt in engines that you don't have to worry about spinning a rod bearing two days after you drop it in, or low oil pressure after a couple weeks... Don't even put yourself in that position. A $650 engine that may need a $1500 rebuild isn't worth the trouble. Buy something good to start with, and you won't have to worry about doing the job twice.
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Old 08-07-2018, 06:25 PM
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Re: 1991 TA LB9 is worn out... now what?

Originally Posted by Drew View Post
Unless you're really strapped for cash, I'd skip the classifieds used engines. For $2,000 give or take, you can pick up an L05 crate engine (12568758) new from GM. For about the same money, or maybe even a hair less, you can pick up a L31 Vortec 350 crate engine, add a TPI Vortec base and you're miles ahead of the L05. Or for a few hundred less Jegs offers a 350 TBI crate that should bolt right up to the stock TPI. https://www.jegs.com/i/JEGS/059/8758/10002/-1

As you can see there are lots of options for nearly bolt in engines that you don't have to worry about spinning a rod bearing two days after you drop it in, or low oil pressure after a couple weeks... Don't even put yourself in that position. A $650 engine that may need a $1500 rebuild isn't worth the trouble. Buy something good to start with, and you won't have to worry about doing the job twice.
Agree - and if you do want to rebuild something get an L31 Vortec from a truck. They are super cheap - I got one with a bad intake gasket (oil/coolant mix) for $200. I tore it down to find nothing at all wrong with it.

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Old 08-07-2018, 06:28 PM
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Re: 1991 TA LB9 is worn out... now what?

The caddy 350 is a roller engine but with the swirl port heads. Re-use your Lb9 cam or get one a bit warmer,rebuild that L05 and buy some reman vortecs or find some 083s cheap and throw on it.
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Old 08-07-2018, 06:55 PM
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Re: 1991 TA LB9 is worn out... now what?

I have I have a complete 1991 5.0 TPI engine from my 1 owner 91z. The car only has 71K miles. Only reason I pulled the engine is to replace it with a built 383 Super Ram. Let me know if you are interested.
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Old 08-07-2018, 07:33 PM
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Re: 1991 TA LB9 is worn out... now what?

Originally Posted by Chiknhawk View Post
I have I have a complete 1991 5.0 TPI engine from my 1 owner 91z. The car only has 71K miles. Only reason I pulled the engine is to replace it with a built 383 Super Ram. Let me know if you are interested.
Thanks. PM sent
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Old 08-10-2018, 03:15 PM
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Re: 1991 TA LB9 is worn out... now what?

Hi there,
I thought I would include some pics of the process. Here is the victim, and the temporary storage, and the car in it's hole, not to move again on its own.
Attached Thumbnails 1991 TA LB9 is worn out... now what?-dscf0412-1-.jpg   1991 TA LB9 is worn out... now what?-dscf0413-1-.jpg   1991 TA LB9 is worn out... now what?-dscf0414-1-.jpg  
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Old 08-10-2018, 03:21 PM
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Re: 1991 TA LB9 is worn out... now what?

My plan right now is to take the motor out and inspect it to see how bad it is. Hopefully the bottom end is saveable with rings and bearings. I have read on here that the 91 should have the better cam, if so, and it is not worn out, I will leave it in there.Also while I have the block out, I plan to replace the oil pump, because, why not? And the timing chain set also, since it has to come off anyway, and is probably a little stretched.

I am pretty sure the heads will need a rebuild, unless someone recommends against the stock heads.
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Old 08-10-2018, 04:36 PM
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Re: 1991 TA LB9 is worn out... now what?

Spend your money on a cam, not an oil pump.

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Old 08-11-2018, 12:46 AM
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Re: 1991 TA LB9 is worn out... now what?

Hi GD, thanks for the reply, but I can't agree on not replacing the oil pump. Maybe a cam AND an oil pump, but the oil pump for sure. At $20, it's just cheap insurance.

Is the stock cam really that bad? Keep in mind this car has 2.73 gears, so it is never going to be a real fire-breather. I am on a really tight budget, I just want to build this engine with a little more power (if possible), at a reasonable price. If you think the cam is really lame, do you know of a good deal on a replacement cam? What do you recommend?
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Old 08-11-2018, 02:00 AM
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Transmission: 700R4 3000 stall.
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Re: 1991 TA LB9 is worn out... now what?

The oil pumps are very durable and rarely fail. But sure if i looks like it could use one....

As for the cam. Just go with the GM ZZ4 Cam:

https://www.summitracing.com/parts/nal-10185071

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Old 08-12-2018, 12:05 PM
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Re: 1991 TA LB9 is worn out... now what?

beginning the teardown.
Here's the punchbowl, and ... OH NO!!! the turd
Attached Thumbnails 1991 TA LB9 is worn out... now what?-dscf0415-1-.jpg  
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Old 08-12-2018, 12:06 PM
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Re: 1991 TA LB9 is worn out... now what?

first up will be labelling all the connections
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