My 390 HiPo was fully rebuilt several years ago but after the rebuild it smoked excessively (Oil smoke). After 100 miles or so, it was so bad that it fouled the plugs. The engine was disassembled and discovered that the valve guides & valves were excessively worn. Pistons, cylinders, and rings were checked also. After reassembly the same thing occured. The heads were redone again at another machine shop with hardened valve guides and another set of rocker arms, and oil supply to the heads was double checked. - It did it again! It has been sitting since then. Any ideas to solve this problem?

 

my friend is haveing the same problem with a freshly rebuilt thunderbird 390, right at start-up it smoked pretty bad out of the left side and none on the right, tomorrow were tearing it down to take a look at the problem, his heads were fully rebuilt also, so i guess we'll see what happens, good luck with yours

 

Don't pull the heads until you look and see if the heads are flooding with oil, I have the same issue(smoke on the left side) but it's only due to the oil flooding. I am getting new rocker setup and restricting oil passages.

Might save some work..

 

The heads may be getting oil flooded but that doesn't explain why the valve guides continue to become excessively worn. That should help prevent that problem, but would cause it to smoke.

 

ill take a look at that first, because the motor runs great it doesnt miss or anything, it just smokes bad out of that side.

 

My next thought would be the orientation of the ring gaps is not right.

--Mike

 

Rings are fine. Ring gap orientation is fine.The real problem is Excessively worn valve guides.

 

Daoz, I'm not sure what was meant by 'hardened valve guides' but I'll throw out an idea. Some shops knurl the inside of a valveguide to bring it back up to size. Some line them with a sleeve of bronze, some press in a new guide made of cast iron ( hard ? ) Are the shops at which you have had these heads done using the correct valvestem seals ? That might account for the oil burning. Are the valvestems straight and do they spec out okay for diameter and concentricity ? Were the valvestems polished before they went back together ? How does the intake fit ? And what does the intake have to do with it anyway, you ask ? If the heads have ever been remachined, and they, or just one of them, was cut out of square, it might put a strange side load on all of the valveguides in that head. And they wouldn't last long at all. It would be tough to see this problem just looking at the heads, and your cylinderhead guy might well not notice it. But it would make the intake manifold fit a little weird, and you MIGHT be to see that on reassembly. Have you considered trying a differant pair of heads ? In my locale, you can buy used heads in the yard for 50$ a pair ( D2TE-AAs ). That and a gasket set might tell you if the problem is the machining of the heads that was done previously. If that fixes the guide wear, then I think you may want to have a discussion with the first shop. DF

 

Did you check push rod length after the machine work ? If valve train geometry is wrong the rocker arm will not sweep the valve stem correctly, putting hard side loads on the stems will wear guides quickly.

 

Adjustable rockers were installed the last time the heads were reworked to compensate for push rod length. Same problem!

 

Hey Dino... I believe you have the answer to the problem. The heads were milled during the rebuild and there is a slight problem aligning the intake. During the last assembly I installed adjustable rockers which have a 1.76 ratio compared to the stock 1.73 and also compensate for the push rod length. (By the way.. I meant hardened valve seats not valve guides. It has the bronze guides).
I also believe that I am getting to much oil to the heads do to a modification during the rebuild (which would of course contribute to excessive oil consumption).
Thanks

 

Adjustible rockers will not compensate for the wrong length pushrods. while now you can get them adjusted right, this will not solve goemetry problems. if there the wrong length, they'll not sweep the stem tips correctly. leading to hard side loading of the stem. wearing them & the guides quickly.

 

How would I know what length to use to correct the geometry? I know they are made .060 over and undersize.

 

Corrected statement!

 

I would start by taking the rocker stands off and laying a straight edge across the valve tips to make sure they are all the same heigth. Put checking springs on #1 valves .you'll need to get a adjustable push rod, or make one out of a old one. put it in and put the rocker stand on. Adjust it so the rocker tip starts sweeping the valve tip at the top and stops before the bottom. Once you start doing it you'll see how simple it is to dial it right in. Once you get the push rod set,remove it & measure it and add your recomended preload to the measurement. Any cam company will make you any length push rods you need.