Complete Valve job or replace engine?

[atcvette]

I have a broken valve spring on my 84. I am looking to either do a complete valve job or replace it with an engine out of an 87. My current engine has 118K, the replacement has 80K. Not sure as to what all I will need to make the switch. Any direction will be much appreciatted.

 

[aboatguy]

If those were my two choices; I'd repair the engine thats in the car. The 87 is a L98 TPI you have a Cross Fire, so there will be some wiring and computer issues to work out. If your going to put up with the swap hassles you may as well find an engine with more oats than a L98 for the swap.

JMHO
MIke

 

[wishuwerehere82]

Pulling the heads on an L83 is a piece of cake once you get the exhaust manifolds and the air conditioning off.
Are you doing the work yourself or paying someone to do it?
I did my heads in about 7 hours not counting the machine shop time.
Do the valve job.

 

[Greg Gore]

What To Do?

Without knowing the car's condition and history I will make some generalizations here. In addition I will assume you are looking for opinions ranging from a quick cheap fix to a more involved rebuild. I wouldn't substitute a different engine with 80K miles. I would see if I could fix the old one. I also wouldn't just pull the heads off an engine with 112K. If you are that far into it why not go with the additional work and freshen the engine? You need to find out if the valve hit the piston (probably did). If so, along with a bent valve it could also have piston damage. In the rare event it did not hit the piston I would be tempted to replace only the springs. The springs can be changed without pulling the heads but you will need an air compressor and a hose with a sparkplug thread type fitting on the end in order to put air in the cylinders to keep the valves up with the retainers removed.

Regards, Greg

 

[atcvette]

Thanks for all the advise. I am probably leaning towards just buying a crate engine and being done with it. I realize there will be issues there to, but it has been a history with this engine and it is about tim it was sent out to pasture. not sure wichich engine I should replace it with, any suggestions there?

 

[markone]

Allow me to throw my two cents in here. By retaining the original engine you keep an important aspect of your vette in tact. You can go crate but you miss an opportunity to do some very neat things to your original engine that you could also do to the crate but would increase the cost of the crate engine.
You could have the the pistons knurled, engine balanced, crank micro polished and cross drilled, heads redone to maximize flow and exhaust, high volume oil pump and some mild cam work. You would be amazed what balancing and blueprinting does to your HP. If your car is not stock then it doesn't matter, if it is, I would keep the original engine. Do not just do the heads, with 118K on the block you will end up burning oil (if you don't now). Unless of course Mobil 1 was always used in the engine.

 

[atcvette]

If I am to keep the engine orginal. Where should I start at in repairing it? Should I get the big things out of the way first, i.e. the internal workings fixed or go with the lesser ones and then move on to the bigger ones. I am looking for a place to begin and a goal to reach.

 

[wishuwerehere82]

If a new valve spring is all that is broken, that's a good starting point. If that doesn't get you going again, then a full rebuild is probably the best way to insure that you don't have to touch anything for a long time.
More speed depends on how deep your wallet is.

 

[I_R_DA_ONE]

The way I go about looking into this problem is as follows;; first see what kind of oil pressure you have and if it is normal (around50#),,, the bearings are probably in good shape.....Next check the compression in each of the cylinders...It should be around 165# (the higher the better)and not have more then 10% differance between cylinders.... if the compresson and oil pressure are good ,, I would just replace the broken spring and drive it... but do check for that bent valve that was mentioned earler...
Mike R

 

[Rogier]

If I were you I would exchange the engine's and all it's computers. The newer engine is always the better choice in my opinion.
Is the newer engine the one with the iron heads? or with the newer aluminium heads?

 

[Greg Gore]

What To Do?

Checking compression is a good recommendation but you will have to replace the broken spring first. If the valve is bent in that cylinder compression will test zero or near zero. As far as whether to repair only the damage, rebuild or replace the entire engine it depends on the condition of the rest of the car and your personal preference. A Corvette will always retain it highest value if it has its original engine and the engine has not been modified; the engine block (and transmission case too) have the vehicle serial number stamped on it. If your desire is to build a hot engine it may be to your advantage to start with a good crate engine. If you decide to rebuild yours back to stock then it will be important to find a good well established and experienced automotive machine shop to freshen the parts, help with assembly or otherwise get everything ready to go back together again. If you decide to exchange the engine with one from a different year it will be necessary to make sure all of the sensors and transducers are compatible with your on board computer or that you can install all the associated computer equipment along with the engine as a complete package.

Regards, Greg

 

[vette747]

I would just replace the spring. My 84 has 300,000 miles and still goes at track. I replace the rod bearing and oil pump twice. I replaced timing chain last summer. The compression is at 150 on all cylinders. Well, if you want a new engine and look to spend some money this is ok, but technically this is not requied. These engines are durable.

 

[AdvancedAutoCC]

Allow me to throw my two cents in here. By retaining the original engine you keep an important aspect of your vette in tact. You can go crate but you miss an opportunity to do some very neat things to your original engine that you could also do to the crate but would increase the cost of the crate engine.
You could have the the pistons knurled, engine balanced, crank micro polished and cross drilled, heads redone to maximize flow and exhaust, high volume oil pump and some mild cam work. You would be amazed what balancing and blueprinting does to your HP. If your car is not stock then it doesn't matter, if it is, I would keep the original engine. Do not just do the heads, with 118K on the block you will end up burning oil (if you don't now). Unless of course Mobil 1 was always used in the engine.

Knurling pistons? That's a great idea for a pig-fighter (car to be dumped at the auto auction), or to patch it for selling, but a monumentally BAD idea for a daily driver streeter and/or performance type engine. Also, working the existing heads is like throwing good money after bad, unless it's just to freshen them to stock specs. You're better to spring for some good aftermarket heads, as they are much more affordable these days.
Doing the aformentioned work to the crank is a good idea for any rebuild (don't forget to chamfer the oil holes), but the OP is likely better off swinging in a crate longblock once all is said and done. "Blueprinting" is one of those romantic racing terms that actually describes building an engine to a close set of tolerances (which is standard prep for any performance engine). Balancing is actually beneficial, but can be cost prohibitive to the "budget minded".