I have a 69 302 that I plan to rebuild this winter. Currently I have a 74 302 in my van. I figure if I rebuild the 69 I can still drive my van, then when the rebuild is done spend a weekend and swap out the engines. Since the 69 does not have hardened seats I'm thinking of replacing them myself. Have any of you done this before. It doesn't seem to be that difficult, just a lot of measuring to check for intererence fits etc. I might end up taking the heads to a machine shop but I was quoted $300.00 from one shop just to replace the seats.. seems quite ridiculous to me!

Randy B

You need the correct equipment. If you do not have the special equipment for doing this job, it will be a pain in the butt. If you have a mill and a cutter that will work, your good. You will have to cut the old seat out (make a cut so the new seat fits) and then press in the new seat. It has to be an interference fit, if not the seat will fall out and slam the valve and head, and the head is done. Make sure your interference measurements are correct. The seat manufacturer will give you this number. My suggestion if you want to do it your self, is to take an engine rebuilding class at your local community college. Here it's only around $50 and you have access to their shop equipment. Also, you will have to give it a valve job, resurface the valve heads, put in new guides, and they have the equipment for doing this.

Vic

I have done it to damaged valve seats. Most often the new seat job will not be good for air flow. A performance shop would do a superior job. I would not do it unless I had to. If the seats are good, grind them. Also, once you cut into a hardened seat on most engines it is no longer hardened. You will do fine with it without new seats. If you were running propane I would possibly do the seats but there is additives in the gas today that prevents valve wear. Not as good as lead but close enough...

I was going to buy a New Way (I think that's how its spelled) seat cutter, 2 of them actually and the pilot guides etc, but all that will run me about 200-250, so maybe the machine shop price isn't too bad after all. In all reality, Ill probably rebuild the 69 block, then pull the heads off the74 engine and rebuild them. the 74 has hardened seats. It'll just mean I'll have about a week of downtime as oppossed to 2 days.

Once you grind the seats on the 1974 heads, the hardened material will be gone. They don't have incerts they just hardened the surface. I would keep the original heads. Changing heads you will be changing compression ratio also.

Clayton

Clayton, Please explain about the "changing heads changes the compression ratio." The heads I was thinking of putting on my 69 engine are from a 74 engine, both are a 302, so shouldn't the compression ratio be the same? Since I think I'll use the 74 heads on the 69 block the only "grinding" I'll do will be lapping the valves! Interesting though, I assumed they all had valve seat inserts!

confused.. Randy B

It depends on the pistons, deck hight, and chamber cc. The 1969 engine should have a higher compression ratio. The heads will interchange but there may be differnt chamber cc. You can check this though. Do a search on cc cylinder heads and you should find an how to.

If your just lapping you should be fine. Just check your valve margin and check for play in the guides. Use new valve seals though.

Randy, unless the valve seats are in bad condition on the 69 heads leave them alone. Yes they are not hardened but unless you are going to work the motor really hard chances are they will last a lot longer than you think or what the manufacture tells you. Seats need to be done by a shop and is not something a backyard mechanic should try simple because done wrong or poorly the seat will come undone and destroy the inside of the motor. I have been told more than once from engine shops if the factory seat is good leave it alone until you have to deal with it. Also the 69 head will have a smaller chamber size and will raise the compression ratio slightly in your case. 74 motor you would put them on still has a dished piston to lower the compression ratio but with the chamber size on the 69 head being smaller it will rasie the ratio slightly and may not be the way you want to go. John