I have a 94 chevy 1500 Z71 truck with 350 engine. Its smokes like crazzy seems to be the heads. I have not checked compresion yet but I am prety sure it is not the rings.  I also have a fairly new crate 305 engine that I put into a 92 GMC 1500 2 wheel drive. The 92 is wrecked I would like to know if I put the 305 heads on the 350 block will there be any complications. Or would i have to mess with the timeing. I did this once to a 84 350 with 305 heads but it had other extras added to it. The 94 will not be used hard or probly ever go over 4500 to 5000 rpm unless passing. Is it workable  

with the cost of mechine work i have found if your going to rebuild the 350 it is cheeoer to contact a place like alabama cylender heads and buy a set of new heads. they come with heaver bases and higher lips whare the valve cover sets on which helps eliminate valve cover leaks. i just baught a set complete with everything but rockers for 380.00 delivered  

If this truck smokes like crazy it's highly doubtful it's the heads. Valve seal leakage will cause some smoke at startup but it's common for performance engine to leave off the valve seals, there just isn't that much oil to burn from there. More than likely this engine is a little tired and there is significant wear on the cylinder walls to cause this.

Some later model 305 heads had 53cc chambers, even though most are 58. Almost in either case you're building a lot of compression. Why make an engine that will ping or have serious detonation with pump fuel? You will need to change the timing, you will need to set it back a lot to not ping on pump fuel, that will make an in-efficient engine.  

Don't even bother with the 305 heads on your 350. Even though the heads will bolt on, the combustion chamber doesn't match up witht he bore properly because of the much smaller bore of the 305 versus the 350. (The 305 uses the same bore as the old 265 V-8, 3.75", while the 350 uses a 4.00" bore)

If you're sure the oil smoke is not the rings, your problem has to be your valve stem seals. I have a '92 Silverado with a 350, I'm getting oil fouling on my plugs because my valve stem seals have gone tits up. I'd recommend you first change all of your valve stem seals (including the o-rings at the top of the valve stem. Don't let anyone tell you they're not needed. I learned this one the hard way myself!)

To make this job easier on yoruself, contact Crane Cams and get their valve spring compression tool, part no. 99473-1. This tool is hte best spring comrpessor out there, and helps to keep you from dropping valve locks down into the motor. While you're there, I'd highly recommend getting a fresh set of valvesprings for your engine.

After changing the valve stem seals if your motor still smokes like crazy, then you either do have a ring problem, or some severely worn valve guides.  

What about Taking the whole 305 and swaping it out and geting rid of the 350. The 92 with he 305 was wrecked and the pully that conects to the harmonic balancer was bent prety bad just worried if it might have hurt the crank and bearings.Wont know till i take it out flip it over and take the pan off Also put a nice dent in the timing chain cover but wont know till i take the cover off to see.  And if the 305 is ok will it match up to the 350 tranny that it being 4wheel drive. Or should i just get rebuilt 350 heads and a gasket set and is it possiable to see if my rings are bad just by looking at the cylender walls. It has 230,000 miles on it It has awsome power no knocks or noise just smokes a little upon start up and vry lightly when driving. Hate cuting corners just donet have much to spend  

I just had a thought. Couldnt I tell if the rings are bad just by a compresion test. If it holds proper compresion and does not drop shouldnt that say the rings are good . What is the proper comprecion for a 94 350 in a 1500 truck. Forgot I have a compresion tester  

I just had a thought. Couldnt I tell if the rings are bad just by a compresion test. If it holds proper compresion and does not drop shouldnt that say the rings are good . What is the proper comprecion for a 94 350 in a 1500 truck. Forgot I have a compresion tester And if this is corect the block should be ok and new heads should make it run great any thoughts  

Cranking compression can give you an idea about the condition of the rings but if there is only some minor smoke then the valve seals probably are the culprit. That is a lot of miles but 305's are a dog of an engine, are you sure you want to have one in a 4WD? It won't be able to get out of it's own way...  

the 305 is a new crate engine with less the 5,000 miles on it . It is the 350 with the high miles. Even before I replaced the old 305 in the other truck it had over 340,000 thousand miles. But if the compresion test is good a new set of heads should make the 350 last about another 100,000 miles > better compresion with platnum plugs and rebuild the throttle body all should be good. If anyone knows of anything else let me know Not everyone knows it all