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Old 02-20-2012, 11:20 PM   #1
dailo
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Default 1991 Stock L98 Rebuild Advice

I am about to replace the transmission on my 91, and thinking while its out it would be a good time to freshen up the engine, I currently have around 70,000 miles. There is a lot of oil mist coming from the breathers, making everything filthy around the engine. Not to mention a few small leaks here and there probably from some gaskets or the oil pressure senders.

Is there a simple rebuild kit for these engines, or would I need to go and get parts piece by piece?

Also, are there any other "upgrades" one would recommend if I am going through this, such as a cam or a rocker change?

Im not a mechanic in this sense, but I am I just looking at changing out rings, or would I need to order both rings and pistons along with the bearings?

Thanks
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Old 02-21-2012, 01:34 AM   #2
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Unless you need to bore the cylinders to remove any taper from wear, you shouldn't need to replace your pistons. But in saying that, if you ever plan to use nitrous, get a set of forged pistons, and ALWAYS have your connecting rods reconditioned or replaced. I'm certain kits are available to supply any level of rebuild you want. My thoughts would be to have the block and crank serviced, then order the kit according to what was required to be done to bring the block and crank to a reconditioned state.


I don't know what your ultimate performance goals are, but for a stock rebuild, try this:
Keep the stock cam, but upgrade the heads with a bit of gasket matching from the intake base to the heads. Also, some work to do a bit of "bowl blending" where you clean up and smooth out the ports under the valves can offer some nice rewards, topped off with a good three angle valve job. As for the rockers, roller rockers are a good option. They free up a bit of horsepower and reduce friction. Unless someone with more experience chimes in, I'd say use rockers with the 1.5:1 ratio. The '91's use the speed density system rather than the Mass Air system and to my limited knowledge, the speed-density is more sensitive/less forgiving to the changes in things that affect the tuning parameters.

Of course port the plenum if you haven't already, don't overlook some smoothing and removal of restrictions, if any in the base manifold, or get an aftermarket base, and maybe some larger aftermarket runners. Top this off with a good free flowing exhaust starting with a set of headers then into a low restriction catalytic convertor, and a good cat-back exhaust system.
I don't know what the laws are regarding aftermarket headers are where you're at, but if needed there options to help open up the exhaust at the heads without alerting the inspectors. And when you get the transmission done, I'd suggest a mild shift kit that will help both the performance and the fun factor.
I know there will be others that will say one thing or another, but this is a simple approach that builds upon what is already there without having to change alot of things around. I say this as I notice your location is in China and it might not be too convenient or practical to go to the extremes some of us have here in the 'States.

Last edited by corvette_bob; 02-21-2012 at 01:52 AM. Reason: just being a know-it-all
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Old 02-21-2012, 01:43 AM   #3
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roller rockers are worth doing. minor clean up to the heads i suppose, thing is, the tpi will choke before the heads do. the tpi base is worth real hp if you port it. the rockers, ported tpi and a set of real headers and exhaust will really wake that car up

absolutely do not change the cam. the 90-91 cars are quite particular to vacuum changes. the stock cam needs to stay unless you retune
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Old 02-21-2012, 01:58 AM   #4
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Thanks, think it will be easier to leave the cam in place.

I have already a B&B cat back system with a high flow catalytic converter along with deleted pre cats.

Would I need new valves and guides as well?
What kind of roller rockers should I put in?

Will search the forum on how to port the TPI.

So essentially, there is no "rebuild kit" or are there people out there that would be able to put one together?

Cheers
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Old 02-21-2012, 03:48 AM   #5
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Originally Posted by dailo View Post
Thanks, think it will be easier to leave the cam in place.

I have already a B&B cat back system with a high flow catalytic converter along with deleted pre cats.

Would I need new valves and guides as well?
What kind of roller rockers should I put in?

Will search the forum on how to port the TPI.

So essentially, there is no "rebuild kit" or are there people out there that would be able to put one together?

Cheers
As far as a "kit", you might not really need one. When you get the block and crank serviced, your machinist will be able to reccomend any appropriate Cam, main and rod bearings you need to use with your application. The same goes for pistons. If you can get away with a honing on the cylinders, you can get a new set of rings and be ok, unless you add nitrous. If your block needs to be bored out, then you'll definately need new pistons to match the new bore diameter. Again, get forged pistons. As a matter of fact, since you're getting the rods reconditioned anyway, my personal approach would be to get the forged pistons and skip reusing the originals. Alot of guys run hypereutectic pistons and have good luck. I'm old school. Go forged with pistons. A good quality gasket set such as a FelPro rebuild set will take care of the gaskets you need.
I highly urge you to invest in a set of high quality, name brand head bolts, main bearing bolts, and connecting rod bolts. Please don't re-use the old ones. That's just asking for failure and heartache.
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Old 02-21-2012, 08:01 AM   #6
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I agree with forged way even if a 2 bolts block isn't the best way to start with for forged stuff...btw my 85 comes from the factory with forged pistons...
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Old 02-21-2012, 08:35 AM   #7
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If youre leaving it pretty much stock you can run a simple 1.6 stock style rocker arm or rocker tip arm. No need at that point for spending more for full body roller rockers. Just get a good brand. With low spring pressure of stockish stuff they will last just fine.
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Old 02-21-2012, 08:41 AM   #8
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Hey guys, dailo lives in Hong Kong. I haven't been there recently but doubt there are many machine shops that would be experienced in the SBC but there would be some. dailo, there are a multitude of parts suppliers that can provide a rebuild kit. Northern Auto Parts comes to mind since I have used two of their kits. But back to basics, you need to find a machine shop who has some experience with the SBC and the necessary equipment to do what needs to be done. Follow their lead based on your goals. Take care in throwing neat parts at your engine since anything added must work in concert with whatever is already there.
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Old 02-21-2012, 11:38 AM   #9
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Thanks again for all the responses.

Yes I'm leaning towards more stock than anything fancy. Would it be possible to not even bother honing the cylinders and just replace rings and use the original pistons?

In other words, could I get away with the following:
FelPro Rebuild Gasket set for my engine
Piston Rings (original size)
Roller rockers 1.6 ratio
Main and connecting bearings
Valve Guides
Head, main, rod bolts
Timing chain?
Water pump was changed 5 years ago
Oil pump?
Rear main seal?
Do I need to replace valve springs?
Replaced the valve seals a year ago
02 Sensor

Anything else I am missing?

Also, I dont seem to be consuming oil, as the level on the dipstick shows the same level between oil changes.

Cheers
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Old 02-21-2012, 11:57 AM   #10
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You can do a backyard type rebuild for a stocker if you want.
Hope for the best

Def at least go get a hone that you can do yourself before putting fresh rings in it. Would recommend a fresh oil pump and timing chain also.
No need for a HV pump either stock is adequate. You can stick one of those hones on the end of a drill get the right grit. Northern auto parts sells them along with rebuild kits. They come with bearings rings etc all you need.

At 70k Id leave the cam bearings alone unless they look real bad (probably be fine). They really dont wear much and only turn half the speed of the crank anyway. Figure half the mileage wear in your head. Those are a pain to replace unless you got the tool....if youve never done it youll botch it up at least once or twice lol.

Id reuse stock fasteners too.

Because of your situation and needs it should be just fine.

Now if was much higher mileage or you were expecting great things performance wise then this isnt the route to take.
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Old 02-21-2012, 01:11 PM   #11
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Quote:
Originally Posted by dailo View Post
Thanks again for all the responses.

Yes I'm leaning towards more stock than anything fancy. Would it be possible to not even bother honing the cylinders and just replace rings and use the original pistons?
I think it's more likely your oil "misting" problem is an issue with top end and/or PVC. Typically, I think of a short block as being much more stable that valves and valve seal. As such, with ONLY 70k miles, I'd be inclinded to leave the bottom alone, freshen the heads, and call it a day. Keep in mind the weakest link with these engines is the head gaskets.

That's because you aren't planning extensive mods, probably don't want to deal with an SD tune, and don't need to perform unnecesary work.

If it took 20yrs to get 70k miles on it, wait until 2032 and 140k mile mark to redo the block!




(Of course, replace all gaskets while it's out...)
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Old 02-21-2012, 01:56 PM   #12
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If you change the rings, you're going to need to hone the cylinders, otherwise the new rings will have a hard time sealing and oil consumption can become a real issue. Since this is a stock rebuild, it might not hurt to replace the valve springs with stock replacements. My '68 Vette busted some valve springs and I'm lucky it didn't swallow a valve. For the cost of quality replacement springs, it might be good insurance. just another .02 .
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Old 02-21-2012, 02:05 PM   #13
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Quote:
Originally Posted by corvette_bob View Post
If you change the rings, you're going to need to hone the cylinders, otherwise the new rings will have a hard time sealing and oil consumption can become a real issue. Since this is a stock rebuild, it might not hurt to replace the valve springs with stock replacements. My '68 Vette busted some valve springs and I'm lucky it didn't swallow a valve. For the cost of quality replacement springs, it might be good insurance. just another .02 .



Honing the cylinders is the only way to break new rings in (w/o boring it).

Last edited by GREGGPENN; 02-21-2012 at 02:07 PM.
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Old 02-21-2012, 10:14 PM   #14
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Quote:
Originally Posted by GREGGPENN View Post
I think it's more likely your oil "misting" problem is an issue with top end and/or PVC. Typically, I think of a short block as being much more stable that valves and valve seal. As such, with ONLY 70k miles, I'd be inclinded to leave the bottom alone, freshen the heads, and call it a day. Keep in mind the weakest link with these engines is the head gaskets.

That's because you aren't planning extensive mods, probably don't want to deal with an SD tune, and don't need to perform unnecesary work.

If it took 20yrs to get 70k miles on it, wait until 2032 and 140k mile mark to redo the block!




(Of course, replace all gaskets while it's out...)
Well we have a saying in HK, you have to double the miles on your car for a realistic reading, haha.
We have such steep mountain roads here, super high temps most of the year, super high humidity all of the time, and loads of traffic.

I'm not in the need for extensive mods, just as long as the car will run fine after the rebuild.

So you guys honestly think I can leave the bottom end alone?
Should I just do a top end rebuild? leave all the pistons and rings in place, or should I look at doing a compression test first?

Cheers
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Old 02-21-2012, 10:54 PM   #15
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you can check cranking compression, a leakdown test tells you lots also.

Should tell you more about the health of your engine beats tearing it down only to find out you didnt have to.
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Old 02-22-2012, 12:42 AM   #16
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Originally Posted by cuisinartvette View Post
you can check cranking compression, a leakdown test tells you lots also.
But how do ya know if any compression issue is bottom or top? More often top-end issues are what causes smoking, etc...

Age of valve seals is the first suspect on my (oil problem) list. Valve guides too.

I think most engines in the 90's can go 200k. Starting with the LSx era, 250-300k and higher.

If you've been diligent about oil changes (and maintenance) and if you haven't had (or see evidence of) head gasket leak (antifreeze), I'd leave a 70k more alone -- thats being returned to stock.

Any increase in compression would change my mind very quickly.
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Old 02-22-2012, 12:45 AM   #17
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Quote:
ut how do ya know if any compression issue is bottom or top? More often top-end issues are what causes smoking, etc...
Top Secret information sir.

Youd be even more dangerous with it.
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Old 02-22-2012, 12:59 AM   #18
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If the work involved in changing the rings and the bearings is not to much more difficult, and since the engine has to be out anyway for a full cleaning and transmission install, think I should just go ahead and get it done?

Or is it a PITA to really remove everything and reinstall?

Thanks!
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Old 02-22-2012, 01:46 AM   #19
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Top Secret information sir.

Youd be even more dangerous with it.
If you tell him, we'll have to kill him!

Wait.... go ahead and tell him!

Sorry GGreg, couldn't resist

Getting back on topic, troubleshooting to diagnose the source of oil is probably the best idea that's been offered so far. If there is indeed a problem, you would be money ahead by finding out the exact nature of the problem. Just don't tell Gregg how you found the problem

Ultimately you need to determine how far you need/want to go into the engine. Should it come to an overhaul, with as many trucks and other Chevy powered vehicles around the world, there's gotta be someone in HK that knows something about machining/rebuilding small block Chevys. OR, what if a suitable short block could be found? I don't know how well supplied the Chevy parts network is in HK, but Australia is within shipping distance, relatively speaking, and there's more than likely a source for short blocks or other components there. You might be able to get a short block with a warranty and be able to skip the lower end rebuild, leaving only the heads to be freshened up, and then the reassembly. I hope this helps.

Last edited by corvette_bob; 02-22-2012 at 02:21 AM.
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Old 02-22-2012, 06:52 AM   #20
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Quote:
Originally Posted by corvette_bob View Post
If you tell him, we'll have to kill him!

Wait.... go ahead and tell him!

Sorry GGreg, couldn't resist

Getting back on topic, troubleshooting to diagnose the source of oil is probably the best idea that's been offered so far. If there is indeed a problem, you would be money ahead by finding out the exact nature of the problem. Just don't tell Gregg how you found the problem

Ultimately you need to determine how far you need/want to go into the engine. Should it come to an overhaul, with as many trucks and other Chevy powered vehicles around the world, there's gotta be someone in HK that knows something about machining/rebuilding small block Chevys. OR, what if a suitable short block could be found? I don't know how well supplied the Chevy parts network is in HK, but Australia is within shipping distance, relatively speaking, and there's more than likely a source for short blocks or other components there. You might be able to get a short block with a warranty and be able to skip the lower end rebuild, leaving only the heads to be freshened up, and then the reassembly. I hope this helps.
No Chevys in HK at all unfortunately, they sold about 30 RHD Cadillac STS's for a period of time before the company went bankrupt.

We have competent mechanics here, although their english skills are pretty poor, so will be me with the FSM explaining what they need to.

The last time I had them replace the valve seals, after opening the covers up, the mechanic said "Oh chopstick engine" "same engine as rolls royce, I know!"

Of course, to him all valve lifter "chopstick" type engines are the same...
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Old 02-22-2012, 06:52 AM
 
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