Timing #3

[siteunseen]

Steve that's pretty much exactly what the mechanic said. Stock engine would benefit most from the cam advance. And won't cost a penny more than what I've got already. Also said if I didn't like the way it ran it would be no problem to go to #1 hole on cam sprocket since the chain is already in the right spot on the crank. But "Don't drop the chain!" I'm sorry to say that I will be doing the reverse of what you suggested, #3 first. Thank you for the reassurance and for reading all that Racer Brown article. It was confusing to me.

[madkaw]

Racer Brown is one of those readings that you have to do 4 or 5 times before it starts clicking. Take small doses, he really does a good job explaining things,but it's a ton of info

[Zed Head]

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.

[LeonV]

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.

Ok...

[Zed Head]

No offense Leon, I didn't even notice who posted the thread. I've read the article before and wondered then where this guy got his ideas from and decided at the time that it was mostly theorizing.

My point was to take it with a grain or two of salt. It's good for understanding what might happen, but short on showing what really does happen. Great seed material for more discussion.

[madkaw]

Mechanical engineer making his own cam designs - and pretty good too- writes based on conjecture

Really?

[Zed Head]

His words (Racer Brown's) imply that he knows what the Nissan engineers were thinking and why they had two adjustment holes. He doesn't offer any evidence for retarded cam timing, using a good condition chain and sprockets though. He just offers an idea of why they might be there. The FSM explains in clear times what they're for - adjustments for wear.

For the record, I have worked with many engineers and know that passing courses and getting an engineering degree is no guarantee of logical, clear thinking. To the contrary, I have met many engineers who assumed that because they were engineers, that their thoughts, on any and every thing, must be correct. "I have an engineering degree, I must be right." As I said, great for conversation, but don't spend your money on what's said until you see the evidence that it's true.

[LeonV]

No offense Leon, I didn't even notice who posted the thread. I've read the article before and wondered then where this guy got his ideas from and decided at the time that it was mostly theorizing.

My point was to take it with a grain or two of salt. It's good for understanding what might happen, but short on showing what really does happen. Great seed material for more discussion.

Any examples of aforementioned "conjecture" regarding the cam write up? Otherwise, your post comes off as conjecture. Honestly, show me what it is that you think is made up and we can discuss.

[Zed Head]

Here's one. His writing implies that the three holes are for power band adjustment, if you're going to run at high RPM. If you want to, they are there for your pleasure. Don't worrying about retarding the cam timing, it's self-adjusting!! Just rev it up higher until the cam timing is where you want it!

"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!"

Another obvious follow-through on this discussion is that retarding your cam by installing it off one tooth and using the holes to dial it in, still retarded, will give more high RPM power. Move the power band higher. Maybe the racers are already doing it, it's easy, and cheap. A little porting work to let the engine breathe, slip the cam chain a tooth, and you're making cheap, easy HP.

[LeonV]

Here's one. His writing implies that the three holes are for power band adjustment, if you're going to run at high RPM. If you want to, they are there for your pleasure. Don't worrying about retarding the cam timing, it's self-adjusting!! Just rev it up higher until the cam timing is where you want it!

"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!"

Another obvious follow-through on this discussion is that retarding your cam by installing it off one tooth and using the holes to dial it in, still retarded, will give more high RPM power. Move the power band higher. Maybe the racers are already doing it, it's easy, and cheap. A little porting work to let the engine breathe, slip the cam chain a tooth, and you're making cheap, easy HP.

Yeah, the 3 holes are for powerband adjustment... what else would they be for?

I don't think you're understanding that statement correctly. To paraphrase: cam timing inherently retards as you accelerate the engine. The cam sprocket has holes to advance the cam. If cam timing is too retarded, advance the cam. I don't see any issues with the statement.

There is no mention of how much it is retarded, but in order to know that you'd need to dyno your own engine to figure out how much advance is needed.

[Zed Head]

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!"

[madkaw]

No offense taken:)

It all makes for good argument. It seems to me Racer was just pointing out an inherent flaw with a large cam chain design. There is no way to eliminate this-even with a good chain and tensioner. I think a qualified engineer could work this out mathmatically.

Yes the holes are for adjusting out additional slack in a chain, but it's more than that. The effect of a loose chain retards cam timing, so you can counter that with advancing the cam timing.

Also, think about how times someone has come along and taken the original design from a manufacture and made it better by further R&D process. Nissan engineers developed something for mass production and it will have inherit flaws, but not a bad design.

I don't think Racer would have made such comments without seeing something on a dyno.

Overall, the article you are refering to is a great educational tutorial on how an engine works, and I am glad he liked to mess with Datsuns, but he also made a name for himself with Mopars too.

I actually came across a racer Brown cam on an e-88 head, I wish i had kept it, but I didn't know any better. It had the single valve springs and it was a mild cam. I would love to hear from the person who bought it to see if they are running it and how it performs.