C3 71 LT1 engine woes

[Peter M.]

71 LT1 - recently purchased 71 LT1 with 411 rear. Car not going like it
should. I am not mechanically inclined. Compression test revealed 90psi across ALL cylinders. Leakdown on cyclinder revealed 105-106.

Do these numbers indicate the probable source of the problem(my 71 service manual states compression should be 150?).

Is there any other possiblities to these results?
Is the only outcome a complete rebuild?
Can one get all the parts for this motor today?
Are thereany know LT1 motor experts out there who specialize in getting the best out of this motor or can any competent engine builder do it?

Any suggested vendors? ALso, Holley Carb is wrong-any vendors out there carrying 71 LT1?

Any help would be appreciated.

Thanks

[Joe L.]

Re: C3 71 LT1 engine woes

Peter-----

The cranking compression readings which you indicated, if they are accurate, are WAY low. This could VERY well be the cause of your problem with poor performance. It's unusual, though, for the readings to be this low and, yet, all about the same. So, it makes me suspect some sort of a testing problem. On the other hand, it could just be a high mileage, well worn engine or a lower mileage, WELL-BEATEN engine.

If you confirm these readings, I would say that a complete engine rebuild is in order. Yes, the problem could be simply the result of worn/"burnt" valves and you could tell this by squiting a little oil in the cylinders before doing the compression test (if you do this and the readings come up, it means that the problem is with the bottom end; if they don't come up, it means that the valves are the likely culprit). However, with this low of readings, I think I'd go for a complete rebuild. To me, doing a "valve job" on an engine which has seen considerable service is for "low budget" driver-type cars in which the owner is trying to get another 25-50K miles out of the car before junking/selling it.

All of the pieces needed to rebuild the engine remain available. In fact, for your 71 LT-1 engine most of the pieces that you will need for a rebuild remain available from GM (if you wish to pay GM prices). The exception is the pistons. These you will need to get from TRW/Federal Mogul or Keith Black-Silvolite.

You can also get high quality, aftermarket items like bearings, piston rings, and valves (if required) from Federal Mogul.

Holley used to make a reproduction of the 4801 carb used on your 71 LT-1. However, I think that they've dropped it now. Check with Holley or Chicago Corvette. They used to have a considerable inventory of the Holley re-release carbs.

[Clem Z.]

Re: C3 71 LT1 engine woes

the leak down is strange because you can only have 100% leak down. was the air leak into the oil pan,exhaust or intake?

[Peter M.]

Re: C3 71 LT1 engine woes

Joe - Thanks for your answers

[ROB DAME MEM# 36211]

Re: C3 71 LT1 engine woes

Have you checked the #s to be sure it's an LT1 engine?
or perhaps the timming chain is off a tooth

[John H.]

Re: C3 71 LT1 engine woes

Or perhaps someone adjusted the valves as if it was a hydraulic cam instead of a solid-lifter cam, and the valves are all being held open a few thousandths, which would result in a consistent major compression loss across all cylinders.