Timing #3

[LeonV]

I guess we all get something different out of the same words. I actually left out the words that got me going, they are below. Racer Brown is suggesting that the original design is wrong, or that the Nissan engineers missed something. Statements like that just get me wondering how the writer came to conclusion, and in this specific case, it looks like a guess.

Cam timing is one of those things that's hard to mess with, without risking damage, and hard to measure results without a dynamometer. Even measured, you have to know what you want before you can say it's better or worse. Do you want oomph or high RPM HP?

It's all good conversation, didn't mean to offend with my engineer comments. Scientists are even worse.

Here are the statements that offended me -

"Datsun chains are quite long, about 42 inches in circumference, with 110 links, which means that keeping the valve timing exactly right at all times, is nearly impossible. It is therefore better to start out with a slightly advance camshaft - say by 3 or 4 crankshaft degrees - because there is no way in the world that it can be kept from retarding itself as the engine is run, particularly at high engine speeds. This is also the reason for the three different timing marks and three different dowel pin holes in the Datsun camshaft sprocket; they make provision for advancing the camshaft in 4-crankshaft degree increments, but they make no provision for retarding the camshaft. It does that by itself with no outside help required!"

I see where you're going with this, but why get "offended". I could care less what the guy does, he can be a ballerina for all I care. That's not what makes his statements right or wrong.

I don't know how much timing is retarded at high rpm, but it sure does not stay constant. Nowhere did Brown say that the design is "wrong" but that it has certain flaws, just like any design. Unfortunately, in the case of the stock chain setup in a high-performance L-gata, the flaw does affect performance. Kameari didn't create their custom chain tensioner for no reason...

In Brown's case, it was "better" to slightly advance the cam, but it is up to the end user to determine how much this matters to them. Will the stock chain limit your 7000rpm, 200hp L28? Probably not. Will it limit a 9000rpm, 350hp L-series? Most definitely! Brown is right (don't know about the numbers, but as far as the physics of it are concerned) but it's up to you to decide how applicable it is to your case using whatever method you like.

[Zed Head]

We're in to the minutiae now. My main point was the old adage "don't believe everything you read." You could also add "make sure you understand what you're reading." Racer Brown's article can be interpreted in many different ways. I don't see anything in it that can be used to decide if the #3, #2 or #1 hole is "better" for a new chain and sprockets, on a stock engine. Cam timing retardation happens, but retardation from what starting point - "optimum" (subjective, and maybe Nissan missed the retardation effect) or already advanced (because Nissan engineers are no dummies)?

After siteunseen has it done and reports back, we can discuss the relevance of "butt-dyno" results,and what oomph means.

Site, maybe you could do some 0-60 runs to give some measurable results? And thanks for the opportunity to hash out some new topics on your thread. Good luck with it.

By the way, it seems that Nissan gave up on the three adjustment hole idea in the later ZX L28s. It's not mentioned in the FSMs anymore. Probably caused too much time-wasting internal discussion among the engineers.

[LeonV]

We're in to the minutiae now. My main point was the old adage "don't believe everything you read." You could also add "make sure you understand what you're reading." Racer Brown's article can be interpreted in many different ways. I don't see anything in it that can be used to decide if the #3, #2 or #1 hole is "better" for a new chain and sprockets, on a stock engine. Cam timing retardation happens, but retardation from what starting point - "optimum" (subjective, and maybe Nissan missed the retardation effect) or already advanced (because Nissan engineers are no dummies)?

Ok... Cam retardation/timing variance happens, but I'll repeat that what's better for him is not necessarily for you. The article's purpose is not solely to tell you which hole to put your cam into. :tapemouth

The Racer Brown article is full of conjecture and guesses. A great place to start for experiments and good ideas to be aware of, but there's no facts to back up the claims. It looks like someone just writing down their ideas of what "must be" happening.

The two extra holes are most likely there for chain wear as the FSM describes.

Well then, it appears as though you made quite the exaggeration in your original criticism of the text then, yes? You were annoyed by his thoughts on what the cam holes are "supposed" to be for and felt like ranting?

Yes, in order to be proficient at reading comprehension you must have some critical thinking skills and be able to "read between the lines" a bit.

[LeonV]

FWIW, I would set the cam "straight up" and go from there. Technically, you can start from anywhere, but straight up is as good a place as any. Steve had it right in post #9, set it to #1 and drive. You can then go by seat of the pants, but that's a crapshoot, so the dyno is your best bet for learning and improving anything in this case.

OP isn't building a race engine. If you're not willing to dyno the car, then it doesn't really matter. Set it to 1 and go, it'll drive just fine.

[siteunseen]

Conjecture and guesses are what put men in space. I've set it at #3 and used red loctite, torqued to 100lbs.

[madkaw]

Well, how did it run?

[siteunseen]

I promise that'll be one of my first post after it is running. Just got the clutch in and re-attached the tranny today so the motor's ready to be dropped in. I still need to solder the new connections for the injectors and cold start before i can crank it. Almost put the header on before mounting the transmission. In my crazy way of re-assembling that would have been a huge mistake because I'm doing it on the floor instead of hanging from a hoist. The bellhouse and transmission is a lot heavier than I thought, so glad I learned from you guys to pull both instead of bench pressing that b***h. Not really the floor but a crate Zedyone showed in his thread. It's taking longer than I thought because it's hotter than I thought it would be in HELL!

Edited July 18, 2012 by siteunseen