valve stem clearance

Any decent valve job these days involves replacing the guides with a good quality guide - typically this is a silicon bronze guide - and reaming the guide to the proper clearance for the valve stem. The proper clearance depends upon the type of valve (more specifically, the type of metal) and a few other design factors. Trying to put new valves in worn/old guides and hoping the clearances are OK is a recipe for failure. Incidentally, the guide clearance is also an oil control factor - it's not just the seal that controls the amount of oil passing through the guide and into the combustion chamber. And, any decent valve job involves a three angle grind on the seat and the valve lip. Five seems like overkill to me, especially because many builders do a poor job (or none at all) of lapping the valves in properly.

It's worth spending some money on good valve work - your car will run better with more even compression over the long haul, and, it'll be a while before you see a bunch of blue smoke on start up.

 

"Five seems like overkill to me, especially because many builders do a poor job (or none at all) of lapping the valves in properly."

But if they do a poor job of lapping in valves, they have no business taking your money. Can't imagine a reputable engine shop not doing an excellent job with head work. It's all done with machines anyway nowadays, and they provide a far more accurate and positive sealing surface than what we used to do years ago - I don't know any performance shop worthy of the name that doesn't use the latest machinery for that. And you'd be hard-pressed to find anybody hand-lapping a valve nowadays.

A 5 angle valve job can improve performance over a 3 angle (which is the minimum that should ever be considered) in many applications. Ideally there would be no "angles" at all and the more angles, the more expensive the valve job. Most eom engines come with a single or dual angle valve job due to manufacturing costs. The standard way "better" breathing was achieved from the factory was for them to simply install larger (1 or 2-angle) valves. But a top quality multi-angle valve job can actually flow better than a factory 1 or two angle valve job using the larger valve.

A good valve job is one of the best places to spend some money and it will get you at least 50% of what a fully ported/polished head will do at a small fraction of the cost. Bigger valves, though common, are not necessarily the best way to get the performance you want because they will compromise low/mid performance to gain top end. With a good valve job and oem valves you can get most of that top end and lose none of the low/mid.

 

I didn't realize your car was that late........a 1982 still had sodium valves?

That's interesting...maybe David can refresh my memory, on the years used.

While I agree on the valve guide issue, if the OEMs look good it'd be a lot of added expense to put in newer ones, which coincidentally don't have such a great reputation, in certain 355s....given that this engine has only gone 27K miles.....

 

Mike, you're absolutely right "they have no business taking your money" - but they do. The stories of exactly that are common and frequent. The problem isn't with reputable engine shops and good work, the problem is with poor work - that's the very point.

Not sure what you mean by "Ideally there would be no "angles" at all" - quite the reverse, one of the main purposes of multi-angle valves is to more positive locate the valve against the seat by way of it fitting precisely across the X- and Y- axis into a shaped mating surface.

The best shops still do hand lapping if asked (for a price), and, no machine can better a trained hand lapping.

 

I will state, as I have before, that virtually all my engine work has been with US v8's. It may be that the 4 valve pentroof Ferrari heads are, from the factory, far superior in every way (I hope so) to US factory heads. Therefore, it may be that some of this valve work is unnecessary/redundant...I frankly don't know. Re hand lapping..every shop I worked with/know of quit hand lapping some years ago because the machined valves/seats were more accurate and flowed better. Hand lapping means each valve can end up with a slightly different "sink" into the valve seat, changing the flow characteristics for each cylinder. It just doesn't work as well as machining the surface to a precise fit. Not saying hand lapping doesn't work - it does but it's not as precise and repeatable.

The ideal valve shape would be a radius around the edge of the valve - no edges, with a minimal seating area. I have been doing some "current" research on this and find that a "radius" valve job is now available, though very expensive. We had fooled with it conceptually "back in the day" (2006 - all those years ago! ) but now it is apparently "commonly" done.

AGAIN, all my experience and work is with US v8s. Engines are engines but it is distinctly possible that the oem Ferrari engines already come with heads/valves set up as per what we would call a performance valve job. But I don't know. It would be interesting for me to tear down my 328 motor and take a look but frankly, I'm not interested enough in doing so since it's running quit well!

 

Guys, I really appreciate hearing all facets of the thought process. I am amazed at the posts about 5 angle valve jobs and blowers and turbos and Tubis! I love it all and still stand on the platform of leaving well enough alone. I have driven and or owned most marks and all things considered I have the most love for driving the Fcar. It was magical to me as a youngster and I have always had an ear for the high reving motor with the top of the pyramid residing in F1. That out of the way let me say I want to drive the 308 the way it was meant to be and maintain it with the same directives----------------if I wanted a muscle car I would buy a ZR1. Long before I purchased this 308 I had talked to an owner of a new F and was disapointed to hear he preferred driving his old 308 because the new paddle shifter felt very automated. That statement sold me on a classic F.
No clothes, just the car,
tom & joni, hiding
PS had to engage my girlfriend, she is of the same school!

 

Cliff,

I have been professionally building performance and competition engines since the late 60's, and quit doing it in 2006. Certainly I did plenty of head work but that was not my primary area of expertise and I did not personally do most of the machine work on cyl heads. I left that to the experts who ONLY did headwork. BUT did all the engine assy/clearancing/blueprinting/dyno testing, etc. I have thousands of hours on dynos and the track and personally dragraced in the Super Stock class in SS/A, SS/B, SS/J. I worked with Competition Cams, Racing Head Service, Cam Dynamics, Ed Hamburger, Ron Mancini and several other companies doing engine work.

I guess we will have to agree to disagree on this. MY personal experience is that no current competition engine would have hand-lapped valves and none of the companies listed above would suggest hand lapped valves. It would be the same as suggesting that you can hand bore a cylinder and end up with a better sealing surface than the machines. It simply cannot be done, regardless of how much I would like to believe in the old "hand-made" methods.

But, as I said, we can agree to disagree!

 

Fair enough Mike. You obviously have a strong technical background and understand the processes we're talking about here. No doubt you're a smart guy on the subject!

Here's how I hand lap, just for some add'l info:

1. After the seats have been ground and matched to the valve lips (typically using a 3-angle grind I use), I use some medium-course lapping paste and just lap them in using a rotating motion by hand, with a simple suction cup and handle lapping tool. Most valve jobs stop prior to hand lapping for cost reasons. I'll then move to increasingly fine paste until I end up with a polished mating face across all three angles.
2. Here's how I know hand lapping produces a superior result - I have a jig which accepts the head and seals individual cylinders against a face. I can pressurize the cylinder with compressed air with the valves closed and seated, up to 300psi - roughly twice that of the regular compression for most engines. After hand lapping, the cylinders will hold 300psi for over 10 minutes before showing any appreciable drop in pressure. After the very best machine job, I'd be lucky for a cylinder to hold 300psi for even a few seconds. Within 5 minutes this same cylinder is down to atmospheric.

The (few) F1 engine builders that I have had some exposure with all hand lap the valves in. I can't speak to all the teams or overall of course, but the builders I'm familiar with have been doing this since day one. I guess everyone has their own secret sauce when it comes to performance engine building, the above is just my $.02 but I totally understand there's a thousand ways to skin a cat and put together a heck of an engine!

Thanks for sharing your thoughts!

 

Glad to hear someone validate my old school hand-lapping method. When I raced FF we found that when the valves were given a radial grind the flow was the best and after a light lapping you could see a very thin line where the seal was created. I try and not loose sight of the fact that these are street cars and not race cars. Drive'em don't re-design'em!! $.02 from the UP

 

Cliff - interesting re F1. I have no hands-on experience (as I've said before) outside US engines re serious engine work and I'm surprised to hear that an F1 engine would utilize hand-lapping of valves. So I have to admit that if they do it, it is obvious that it cannot be losing them any power since that wouldn't be acceptable at all. Now makes me wonder about the whole process. I have seen flow bench results showing slightly increased flow with machined valve surfaces over hand-lapped surfaces. BUT now, based on your info, I'm wondering if the issue is more related to repeatability and consistency. In other words, the machines can do a better job than the "average" back yard valve lapper with a can of valve grinding compound and the suction cup stick but maybe NOT better than someone who is really good and takes the time necessary. After the machines did the valve/seat surfacing, we checked the sealing surfaces with Prussian blue - they weren't just assumed to be ok after the work.

Maybe that's why "we" went to machined valve surfaces - because the time/care needed to do it by hand and do it well was not cost-effective. I don't know this, but I guess it is entirely possible. A machine will do it the same way every time if routinely cared for and adjusted. But the person could not be so good OR not so good that day. Hmmm...

I know a guy even older than me(!) who was very involved at Racing Head Service in Memphis when they moved to machining valves. I haven't talked to him in years but now I'm interested in seeing if I can get hold of him and get his take on the reason it was done at the time.

Always fun to learn new stuff or, sometimes, to find out the REAL reason things are done...