Thread: 305 build questions

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Well it would appear that you’ve got yourself a project here. The 305 is a good little motor, but not typically associated with a lot of builders for horsepower. You can achieve 250 however, but first things first.

1. Your oil plug should be removed and replaced. At this point, you’d be best off to take the block to a reputable machine shop for several reasons, not least of which is to have them drill and re-tap this hole. You’ll also want the machine shop to hot tank the block, remove all the other plugs and replace the soft plugs. Have them check the alignment on the main bearings as well. This is critical, especially if you did not mark the original positions.

2. The ring you’re referring to is a “ridge” that is caused by the rings wearing into the cylinder. Again, this is a machine shop consideration and in all likelihood, your engine will require boring. A machine shop will bore (as required) and hone the cylinder walls to facilitate the seating of new rings.

3. The wrist pins are pressed in. Removal requires a press. I hope the heat has not harmed your rods. Take the assembled pistons and rods to the machine shop and have them check the rods. If they’re good, they can be reused. If not – well, a new set is in order. At the same time, have the machine shop install your new pistons. I also hope that you marked each rod as you disassembled them to allow for placement back in their original spot. This is important, especially in a “well used” engine as there is a wear pattern on the entire reciprocating assembly.

Now with all that said, you may want to just purchase a complete rotating assembly kit from Summit, Jegs, PAW, etc. like the one shown here. It will run you $600 or more, depending on options like forged crank and what compression ration you’re opting for. It would certainly be worth considering before spending a ton of money on your current crank and rods – especially if the rods need to be re-worked. This way you also get main and rod bearings matched to your crankshaft. I’m assuming that you’ll need new pistons in any case. You’ll want to have the machine work done first so you’ll know what size pistons (i.e., +.10, .20, .30) to buy.

4. As to cam – stay with a mild “aftermarket” from Summit like their K1102 which includes new hydraulic lifters with the cam for about $90. Have new cam bearings installed by your machine shop. Also buy a “true” double roller timing set from Summit (Comp Camp 2100 – about $30) and stick with basic (stock) timing settings. If you have questions, call the folks at Summit. Heads are a bit limited on the 305 but the GM Performance 12558060 is an exceptional cast iron head with 64cc combustion chambers, 170cc intake runners, and 1.94/1.50 valves. They’re about $600 a set and use the newer (Vortec-style) intake manifold and self-aligning rocker arms.

5. Intake manifold choice is a matter of preference. Many on this site like the Edelbrock Performer RPM with a 600-650 CFM carburetor. This is a winning combination and will run you about $600.

After reading all of this – I would recommend that you construct a spread sheet to list all of the components discussed, i.e., machine shop work, rotating assembly, heads, camshaft, intake and carburetor and then add in the following:
Distributer
Oil pump
Gasket set
New spark plugs and wires (don’t forget wire looms)
And don’t forget any “bling” (chrome stuff) that you may want to put on this engine.

Add it all up before you start and you may find an assembled engine will be more practical. I certainly do not want to discourage you from building a motor – but weigh the total cost (especially of a 305).

Remember too that you will need an engine stand and lots of time and patience as well as some specialized tools (piston ring compressor, torque wrench at a minimum). Above all, make sure if you do decide to do this yourself that when you get the block back from the machine shop you scrub it to death with hot soapy water (I like Dawn detergent) and dry it good with soft rags and compressed air. Paint the outside with a good grade engine enamel (rattle cans are fine) and lightly oil every nook and cranny that you don’t paint.

Buy a good Chevy engine book from Amazon or your local book store and study it like there’s no tomorrow. Keep it handy for all of the fine points during assembly, especially sequence of how things go back together and the appropriate torque values. Use the book to reference places for and types of assembly lube as you put things together. Go slow and above all, have fun.

Regards,
Glenn

thanks so much. great info.

apologies if this reply duplicates my previous reply - first one went to moderator for review for some reason.

bought this engine for 100 bucks complete, and my intention w it is just to learn. i want to build a 350, and thats one i'd sink more $ into.... so with this one, i was thinking i wanted to get it running and maximize reusing existing parts where feasible. but soudns like I'd probably have to spend quite a bit. so probably the best thing is to get my "100 buck's worth" reassembling and learning on it without trying to really get it running. And then take the thing to an engine shop and 'trade it in' for a few bucks (literally) toward the puchase of a 350 block that i really want to spend money building up.