Car currently has 71,100 Miles
All original, except I added flowtech headers and magnaflow mufflers(yes, I have the original manifolds)
Car runs strong, but if I lean into it it will puff blue and burn some oil
I want to keep the car as original as possible
I am having the engine pulled out, and will have the shop do a complete re-build
Anything to look out for?
Any suggstions to do/add to the engine?
Change cam,stroke it,etc..? > I dont think I want to do this, since I do want to keep it original and reliable
Most important, once I am spending the money I want complete reliability once all is completed
Also, I will put in a dewitt radiator to keep her cool
As always, I look forward to yor replies

 

I am currently rebuilding an LT-1 engine.

You are fine with the heads...those are actually pretty solid, high performing units.

The cylinder walls will be your downfall. If you need to do anything other than a minor hone, you will need to purchase new pistons. Larger TRW 11:1 mini-dome pistons to fit a bored engine will cost a pretty penny, I figure.

As far as originality, I don't see any harm in upgrading to a full-floating rod while you are in the engine. I understand if you want to use the same cam profile, but unless the car has had a zinc additive run in it for the past 20 years, I would suspect that you have cam wear. And you can't just replace the cam in a solid-lifter engine.

So. If it were my engine, I would:
-Polish and straighten the crank
-If the engine needs a bore, replace the pistons
-If replacing the pistons, replace the rods also
-Balance the rotating assembly
-Re-work the original heads with hardened seats and new springs, etc...this will be $700 or $800
-Replace the cam, lifters, pushrods, and rockers. Personally, I'd go roller the whole way through, but if you want to keep it "original", just get all new stuff.
-Replace plastic-gear timing gear with new double-roller gear and chain
-Replace oil pump

Having the car "original" doesn't include putting tired parts back in the engine. But I'd be faithful to the original parts...all forged...nice stuff

If replacing the pistons, I would seriously think about if you want to maintain the 11:1 compression ratio. One of the reasons you're having issues could be detonation you can't hear pushing the piston skirt around and 'egging' the lower portion of the cylinder bore...my engine had barely 10,000 miles on it and I had evidence of it. Fortunately (or unfortunately) I was forced into a rebuild for other reasons before my bore got ruined.

You can keep the pistons (or that piston style) and thicken the head gasket a bit. Or you can run premium fuel and an octane booster.

If you don't replace the cam/lifters, you run the high risk of wiping the cam later and having all that metal back in the engine, forcing you to rebuild the thing again just to save all the work you are doing now.

Them's my thoughts.

 

Personally, I would use flat top pistons. They'll drop the compression down to 10-1 or a little less which will run on premium gas with no problems.

 

Thank you Keithinspace
Great re-cap and I will review with the re-builder
My feeling is a rather spend the money once, so when everything is opened I want to replace All that is necessary
Good luck with your LT1, and Please keep me posted on any additional finds or recommendations

 

If I had an "all-original" '71 with the LT-1 engine, I'd want to keep everything I could see 'original'. If you want to freshen-up the engine, do the check-out and machining as suggested, clean up those LT-1 heads, and put some new [and better] pistons/rings/rods/bearings in it. Put the intake manifold back on and have at it.

If you are destined to put more money into it, put a nice performing roller cam and lifters in it.

If you want a 'monster engine', remove the LT-1 engine to rebuild it; then bag it for posterity and stick a crate engine [with the power you want] in the car. At least, you won't be tearing up a good, original LT-1 engine while you're playing around.

 

I just remembered that in 1971 the LT-1 had 9-1 compression, so it's fine the way it is.

 

Is the car overheating? Have your stock radiator tanked and checked.

 

MrSki,
I experienced a similar thing. I also have a '71 LT-1 that would puff some smoke regularly. My problem was worn valve guides. I have removed the heads and had them rebuilt. Many of my guides were out of tolerance. The valve seats were all beaten as well. I had the heads rebuilt, new guides, valves, springs, locks, and had hardened seats put in. Bill was just under $800.

With the heads off, I inspected the lifters and found they were all worn and three of them worn badly. I then decided to replace the cam and lifters. Crane Cams has an exact replacement for 330 horse LT-1's. They actually offer two different grinds. I contacted them directly and they were very helpful. They explained the difference and making the decision was easy.

Like you stated, keeping original was very important to me. The solid lifter cam set up is a big part of what makes an LT-1 and LT-1. I was happy to find direct replacements. There is also new lifter technology that helps oiling. Comp Cam makes these, they are called DSM oiling holes. They are on the face of the lifter.

I did not pull my motor and I also left the bottom end alone. There are certainly lots of opinions to go both ways. My car has 49k miles. The cylinder walls did not have any edge or lip. I also had good compression on all cylinders.

I'm now in the process of putting it back together. I'm mostly painting, but assembly should start in a couple weekends.

Guess I'm sharing my experience because its similar. And also wanted to let you know that there's "stock-like" options for your rebuild

Dan

 

I had a whole response typed and the stupid thing got lost. This is a more abbreviated response:

I decided on full floating since I was $225 into rod reconditioning anyway. A new set of Eagle forged rods was $275. It is a simple matter of replacing an unknown (rods with 71k miles on them) with a known item of slightly higher quality material. The TRW pistons already have the snap ring slots for full floating, so why not go ahead and reduce a small bit of friction while you're there?

As far as the valvetrain, the parts are just too cheap to replace and the new parts are better. No reason to risk putting old parts back in there when $100 would get you higher quality replacements. And my engine guy has had catastrophic failure in the past when keeping used solid lifters on new cams. Just one of those things. Once you go through that surface hardening, they get chewed up in a jiffy. He just doesn't do it anymore.

And my limited understanding is the no-lead fuels are rougher on non-hardened seats. If you're redoing the heads anyway and need to grind (or replace) the valves, there isn't much of a reason not to get the hardened seats. Like Mr. Dan H, I would have been $700 or $800 to get my camel hump heads rebuilt. A good way to go if you want to keep the heads. And those really are fine heads. I'm just going a little more 'outside the box' with my build.

And yes, I was incorrect on the CR. That is when they dropped it down. So you are fine with your pistons if you can keep them.

In my post, it was from the perspective of replacing all the old parts you can to increase reliability. No reason to put a 71k old pushrod in there, perfect or not, when a new set is very inexpensive. Same with lifters and rockers.

 

I'm not as skeptical of the reliability of the original parts. If they check out OK and don't have any cracks (Magnaflux check), I would be fine with putting them back in the LT-1 engine...either to keep in the car or to store for 'later'. Today's aftermarket part quality is 'suspect', at best. Even new parts should be checked for critical tolerances and cracking, IMO.

As I've mentioned before, if you keep the original engine in the car, I would prefer to put new cam/lifters in it and get the original heads reworked. Other than that, a good cleaning, then bearings & gaskets should be all it needs. If you are going to store the engine and the cam/lifters don't show any abnormal condition or significant wear, I wouldn't even change them. I'd choose to put the money into the new crate engine.

But, that's just me...

 

You're not reducing any friction. Just distributing it to different surfaces. It won't make any difference.

Cheap replacement parts are not always better. I've seen new parts fail too.

I agree you shouldn't put used lifters on a new flat tappet cam, solid or hydraulic. If it sounded like I was suggesting this I'm sorry because I wasn't.

Like I said, hardened valve seats are not required for any motor unless it's going to be heavily loaded for long periods of time. Of course machine shops won't agree with this because they want to sell you the hardened seats.

 

Honestly, I don't want to split hairs. It's not like there is a tangible performance difference between pressed-in and full floating.

HOWEVER, by virtue of there being more surfaces capable of rotation, there is mathematically less rotation that needs to take place on any one surface. Since the skin of oil between the wrist pin and the piston naturally resists motion through viscosity, there is less energy placed in that particular skin of oil because it has to resist less motion. Less energy spent against the viscosity means less heat. Less heat means less friction.

I wouldn't suggest it if the TRW pistons did not readily accept full-floating wrist pins. But they do, so it is an option. I am not aware of a downside to full floating, and though I freely concede that the difference is negligible, it is an "upgrade" that makes later work on the engine that much easier.

Pushrods, for example, cost $120 for the really nice Chromoly heat treat Trick Flow jobs that are considerably stronger than stock. I just don't see re-using wearable parts in a new engine build. What if the rings looked great? Just leave those in, too? The bearings? They're all wear items and intended for replacement.

Yet again with the valve seats. If you're getting a valve grind (or new valves) anyway, what does it cost extra to get hardened seats? $100? Seems like a no-brainer to a no-downside change that would cost you another $800 to fix later (not including removing the heads again) if you decide to go the other way.

The OP stated "complete reliability" in his goal list. If $100 gets him arguably closer to that goal, then why not do it?

 

Thank You Everyone
I am printing this out and going to discuss with the re-builder
I have had no real overheating problems, but I will put in a dewitt rad to be safe(I will keep the original)
Anyone put a Dewitt in a LT1??

 

The total amount of rotation is still the same. Hence, no change in the amount of friction.

Like I said, if the engine is going in a dump truck, by all means have the hardened seats installed.

 

Ummmmm, no.

Honestly...the difference is so miniscule it isn't worth discussing. But for some reason, I don't like the "ROFL" smily thingy being used on me when I know I am right.

Fact: By having a wrist pin floating in the connecting rod instead of press/interference fitted into the connecting rod, the average rubbing speed (velocity) of each of the three bearings is halved.

The energy transferred into a viscous fluid is LOGORITHMICALLY related to the relative velocity of the shear boundary layer. Not LINEARLY or DIRECTLY related. Therefore, half of the shared shear velocity does NOT tranfer into half of the energy transfer. On a logorighmic scale, it could be dramatically less energy, depending on the viscosity of the fluid.

Without getting into the comparisons of Reynolds Numbers of newtonian fluids, suffice it to say that engine oil is in that 'high viscosity' range where a halving of the relative velocity between the shear planes (the piston and the wrist pin) will have a significant difference to the energy transfer to the viscous fluid. If we were talking about water, the discussion would be VERY different because the Coefficient of Viscosity is about 300 times lower, such that the relative velocity would NOT be in that range where there is an appreciable difference in resistance. But we're talking about engine oil with a high Coefficient of Viscosity (0.29 vs. 0.001 for water).

Mathematically, there is less energy transfer into the viscous fluid (resistance to motion...friction) at the connection. Period. There is no debating it. And in this PARTICULAR connection, less friction means less resistance to motion. Less resistance to motion means less "moment" tranfer to the piston. Which means it is not rotated against the cylinder bores with quite as much force.

It doesn't sound like a lot, but my engine runs at 2,500 RPM when cruising at 60 MPH. That means the piston goes up and down 41.67 times each SECOND. That means that in my single 20 minute cruise into town, the piston goes up and down 50,000 times. And I have yet to drive home.

A miniscule difference in the velocities between shear planes relative to the media viscosity really starts to add up after millions upon millions upon millions upon millions of goings-up-and-downings.

Therefore, I politely offer that there IS a difference, but not enough of a difference to count in horsepower. It is measured after 50,000 miles.

Pressed in is just fine. Fine as wine.

Full floating is slightly better. And if he is replacing the rods, the OP should know that the option is available.

That's all I was trying to say, for Pete's sake.

 

So what you're saying is the difference is so small it would be extremely difficult to even measure, therefore not worth paying to have done?

 

anybody who would use a used flat tappet lifter on a new cam would NOT be working on ANYTHING i own. the only thing i would add to the list of things already mentioned would be do some bowl work on the heads a 3 angle valve job and back cut the valves.

 

do a compression check or a leak down test.you mite only need new valve guides and seals.maybe only rebuild the heads if the short block is ok.consider a 383 rotating assembly starting at $900 and up .comp cams ex268 seem to be a good upgrade cam ,not to radical but good power gains.

 

I had hardened valve seats installed in my 300-hp '70, because those heads were not [originally] intended for use with unleaded gas and therefore did not have hardened seats. I have read numerous places that Chevrolet began using induction-hardened valve seats beginning in 1971...true or not?

 

The need for harden seats was explained to me as follows:

If you had a station wagon pulling a trailer across the desert in the middle of the summer.

Bob