Ferrari Life Forum banner

1 - 7 of 7 Posts

·
Registered
Joined
·
83 Posts
Discussion Starter #1
Hi all,

After a few months of ownership and the first proper long drive, I dug through the paperwork that came with the car and rang the workshop that had rebuilt the engine about 18 months ago and two owners ago.

I ended up talking to the guy who had done the work, which was very reassuring. He remembered the job in great detail and expanded on the sketchy details on the invoices for work done.

In summary, the car had come in with a broken engine as some of the original sodium filled valves had failed, which had chewed up piston tops, heads and also caused some lower down damage.

Engine was rebuilt with stainless steel valves, and higher spec, h/c pistons along with new belts, bearings, idlers and so on. Carbys were rebuilt after being found to be full of what looked like little barnacles!

He remembered being very happy about how the car came together and how it went when back on the road.

So in summary - very happy that the documentation that came with the car has been substaniated, and that the work done was at the higher end of possibilities. For the record, the work cost around $26k australian, which included clutch and gearbox rebuild also.

Cheers

Kon
 

·
Registered
Joined
·
575 Posts
This is a problem with these engines.

It's not so much the exhaust valve's fault, but rather the soft guides they travel in. As the guides wear, the valve wobbles side-to-side and when it finally lands on the valve seat when closing, it does so at a very slight angle. There's an incredible amount of force that is concentrated on that small point on the valve head and because the valve stem doesn't have much "meat" (the stem is hollow and wall thickness is about 1mm), it doesn't take a lot for it to bend. The valve material is quite hard and not very forgiving. It doesn't take much longer after that point for the valve to eventually break.

I was very lucky with my car. After buying it, I promptly took the engine out and did a top-end rebuild. I had three bent exhaust valves. A ticking time-bomb!
 

Attachments

·
Registered
Joined
·
3,627 Posts
Peter

Is that a wood frame you have around the forward portion of the engine compartment?

Neat idea.

It interest me as I am looking for a 308 GT4 to rebuild and redo.
 

·
Registered
Joined
·
83 Posts
Discussion Starter #4
This is a problem with these engines.

It's not so much the exhaust valve's fault, but rather the soft guides they travel in. As the guides wear, the valve wobbles side-to-side and when it finally lands on the valve seat when closing, it does so at a very slight angle. There's an incredible amount of force that is concentrated on that small point on the valve head and because the valve stem doesn't have much "meat" (the stem is hollow and wall thickness is about 1mm), it doesn't take a lot for it to bend. The valve material is quite hard and not very forgiving. It doesn't take much longer after that point for the valve to eventually break.

I was very lucky with my car. After buying it, I promptly took the engine out and did a top-end rebuild. I had three bent exhaust valves. A ticking time-bomb!

Hi Peter

Thanks for the extra info - I hadn't heard the full explanation for sodium filled valves apparent weakness before. I like the photo's - looks like you love doing a 100% job.

Cheers

Kon
 

·
Registered
Joined
·
575 Posts
Peter

Is that a wood frame you have around the forward portion of the engine compartment?

Neat idea.

It interest me as I am looking for a 308 GT4 to rebuild and redo.
Yes, in fact, it's a type of particle board ("MDF - Medium Density Fiberboard". Easy to cut and leaves soft edges - less likely to splinter) cut to match the angles and profile of the opening. Adequately protected on the opposite side to protect the paintwork.

Absolutely necessary to have. You have to lift the engine at awkward angles and move it around a bit to wriggle it out. I gently hit the boards a few times while moving the engine around so it kept the paint from being scratched! I was worried more about the rear window as they are almost impossible to find!
 

·
Registered
Joined
·
575 Posts
Hi Peter

Thanks for the extra info - I hadn't heard the full explanation for sodium filled valves apparent weakness before. I like the photo's - looks like you love doing a 100% job.

Cheers

Kon
Like I said, there's nothing wrong with the valves themselves, in fact, many other manufacturers still use them today. They do a good job at withstanding high amounts of heat, especially in todays fuel-efficient (and hot-running) engines. Much cheaper than using titanium!

In the 308's case, they were necessary as in U.S. market applications, air injection was used to clean up the exhaust gases (the oxygen in the air turns CO into less-toxic carbon dioxide). But, the air was blown directly at the back of the valve head. The reaction causes an incredible amount of heat (on top of the heat generated by the combustion process)! The sodium in the valve stem draws the heat away from the valve head and disipates it through the valve guide and into the cylinder head.

As for my pics, well, it's alot of fun and challenging. Very satisfying when it works out in the end.
 
1 - 7 of 7 Posts
Top