Valve spring upgrade advice

[Kronoss]

Hello,

Bent 6 intake valves at the track last weekend, and assumed a timing issue was the cause.

After removing timing gear and related components, all appears to be in order (no missing teeth on gears, tensioner in good shape). Also, the oil pump/distributor drive gear is fine.

Now I'm thinking the valve springs were at fault. I didn't build the engine that's currently in the car, but it certainly appears that the head ( an N47) is equipped with stock springs. I'd like to just upgrade the springs and run this engine as-is with current cam (after repairing the valves)...any suggestions on valve spring upgrades?

I had the engine at 6000-6500 RPM frequently, so I need a setup that will live in that range.

Thanks for any feedback

-Mark A

[preith]

Mark,

You're new, so not to harp on you too much, but this post probably could have been continued with your last thread stating the initial problem, which I'm sorry to hear about by the way. My luck hasn't been too good either, particularly at that track.

What are your cam specs? What manufacture, or is it stock? If it's stock or even slightly larger, IMHO I'd say stick with the stock springs, even at those rpms. I'm just going off my somewhat sketchy memory, but something like 460 or less in lift and I think you're ok with stock springs.

One of my beefs with Scheider for example, and probably most others, is they stock one spring to ecompass their entire line of cams and the end result is a spring which is overkill almost all but the most aggressive cams.

Also, I left you a private message back when you first posted pics. I'd be happy to help you off line as well. From the track and date you have listed you were at a Midwest Council member. I'm also Council member who runs in vintage, but the car is still down at the moment, maybe I'll see ya soon at the track, hope to make it to the June 24th weekend at Blackhawk.

[jmortensen]

When I built up my last head I used the Schneider springs and my machinst and I were talking about acceptable seat pressures and the Schneiders were actually pretty reasonable. There is another cam manufacturer that uses some SERIOUSLY heavy springs. I think it's ISKY, but not positive, might have been Crane, but anyway we were looking at different specs and the Schneiders were the much better choice for seat pressures. I'm not a big fan of their cams, but the Schneider springs seemed like a pretty good option at the time.

I think something else happened though. I've never seen anyone with bent valves blame the springs. I think because you'd have to keep accelerating through the valve float to get them to start crashing into pistons, which is fairly impossible. I'd suggest you have your machinist figure out what happened and don't let us tell you what it was via the internet.

If I had to take a swag for fun, I'd guess that the dowel in the cam sheared or came out, but that is a guess only.

[Kronoss]

Thanks, prieth...I'll contact you privately. I'm new to this forum posting deal, so I'll combine posts in the future.

Yes, this valve destruction happened at Blackhawk last weekend. I'll be there on the 25th if I can diagnose my engine problem.

[preith]

That's a good tidbit about the springs Jon. I was getting a little off subject with that anyways, I think you're right, it probably wasn't valve float which caused it, but my first guess would be the cam dowel as well.

[Kronoss]

I did notice the cam dowel was missing, although I thought it came adrift whan I removed the timing gear from the cam. I looked under the car, etc but haven't found it yet...so perhaps that was the cause of the problem last weekend.

[Zedrally]

If the pins gone missing then It's a fair bet it will be floating around in the oil sump.

Looks like you've got a big job ahead of you, I've been there and cursed the floating dowel. I keep it on top of my monitor to remind me to keep checking it for thightness!

Luckily, heads are generally re-buildable, good luck..

MOM

[jjones-lg]

Don't worry about the dowel in the crancase. Unless you've changed the stock pickup the screen will keep it out of the pump. If you bent valves and the dowel is missing it sounds like the cam bolt might not have been tight. I saw that happen a couple of times and it was when the tech left the cam bolt loose.

I've used the Schnieder Springs and Isky. I've Schneiders on everything from 480 lift to 620 lift and they work fine. Not sure there is such thing as overkill.

jj

[panchovisa]

If your still looking to upgrade your springs I have an option. Try the valve springs from an 810 DIESEL. They are the same static length and the same stack height as stock springs ,but they are 80# stiffer.

The first time I autox'ed my car I threw a rocker arm completely out. A good friend who was an early(1600 Roadsters through first 300Zx) factory Datsun tech (now an engine mechanic for Nortwest) gave me that info. Made the change and engine runs great at higher revs (7 to 7.5 K) with no concerns about top of engine.

[Kronoss]

Thanks for the valve spring tip, Ponchovisa. By the way, you must be right in my general vacinity, since I live in Prior Lake. Beautiful car you have there, be great to see it sometime.

Regarding the cam bolt/dowel combo, I don't know off the top of my head what the tourqe specs on the cam bolt are, but it certainly couldn't have been close to spec as the thing was not real tight. As for the dowel, other than constantly checking the thing, is there anything else I can do to better secure it in the future?

–Mark A