Should I rebuild my engine

[Peter B.]

Hey everyone - Here is another area I need guidance on. I will be checking the compression of my 71 small block today. It is original and has never been rebuilt. It idles a little rough but I think this is partially caused by a vac leak I have. However, there is a small valve noise on one cylinder.

What should my compression be on the Cylinders (+ or - how much)?

My thought is that if the rings are OK (i.e. pretty good compression), I can have a valve job done and not rebuild the engine. I figure a non-rebuilt original engine is worth more.

What do you think and what compression should I look for?

[Duke W.]

Re: Should I rebuild my engine

Is it the base 350 or the LT-1 option? What is the mileage and rate of oil consumption?

Compression pressure and tolerance along with the proper procedure for checking, such as blocking the throttle open, should be listed in your Chassis Service manual and may vary depending on the engine option. Since gages are not necessarily absolutely accurate you should focus on the maximum range of readings rather than being overly concerned with absolute values.

Assuming it's not a mechanical lifter LT-1, valve ticking is often caused by varnish/deposit build up in hydraulic lifters, usually referred to as "sticky lifters". Using HD diesel engine oil will sometimes clear them up due to it's higher dose of detergent/disperant additives, and I recommend HD diesel engine oil for ALL vintage engines that do not have catalytists.

Duke

[Al C.]

Re: Should I rebuild my engine

Peter -
I just performed a quick-check of compression uniformity on my '58 by observing the starter current waveform (with feed to coil disconnected), using my laptop-as engine analyzer technique. Here's what the result looked like:
You might want to try this simple technique.
... Al '58 245hp

[Patrick H.]

Re: Should I rebuild my engine

Peter,

If I recall, you have the base motor.

How many miles at present?

Patrick

[Peter B.]

Re: Should I rebuild my engine

Yes, I have the base motor and to my guess, it has about 80K on it. I say this because the Spedo cable, when I bought the car was broken. My estimates are based on general wear signs.

[Patrick H.]

Re: Should I rebuild my engine

Part of the reason for asking about mileage is to guess what stage the engine is at.

With 80k, you can likely get away with just doing the top half of the engine.

Have a leakdown test done on the engine as this can help you figure out what's going on. It will help you decide if the rings are still OK or the valves are the problem. Assuming they are, I'd do the heads, and consider the camshaft. If nothing else your valve stems seals likely need to be replaced. On my 71, when I rebuilt it at 108,000 miles the bottom end was in excellent shape and could have gone another 108,000 miles. The valves, however, had receded into the heads and the camshaft was very worn. While replacing a camshaft with the motor in the car is not easy it can be done, and would be cheaper than rebuilding the entire engine. If you especially find that you need to replace lifters, you might as well do the camshaft too.

Patrick

[Peter B.]

Re: Should I rebuild my engine

Thanks Patrick