Changing cam timing?

[Guest 2slo4u]

Does anyone have any advice on cam gear timing on the l28et engines? I recently changed my tensioner and chain guides and I changed the cam positon from 1 to 2. I did this because the book said to if the notch on the cam gear was on the wrong side of the dash on the thrust plate.

Now the poer maxes out at a much lower rpm and it wont even rev past 5500-5800rpm in neutral. I can't even hit the redline if I want to. Before I changed the cam positon, the car would run 123 mph now it's hard to get above 100.

Does anyone think I should change the cam back to positon 1? I read on another site that it would even have more horsies with the chain a little stretched and at position 1. Is that true? If so, I will be putting it back to 1 today. If not, I'll try to figure out something else since I had to remove so many things to access the timing chain components.

 

 

P.S. Three speeds(automatics) suck for traveling to visit relatives, unless you like to see the rpms at 3500-4000 the whole trip. Still runs cool though.

[TimZ]

Now the poer maxes out at a much lower rpm and it wont even rev past 5500-5800rpm in neutral. I can't even hit the redline if I want to. Before I changed the cam positon' date=' the car would run 123 mph now it's hard to get above 100.

Does anyone think I should change the cam back to positon 1? I read on another site that it would even have more horsies with the chain a little stretched and at position 1. Is that true? If so, I will be putting it back to 1 today. If not, I'll try to figure out something else since I had to remove so many things to access the timing chain components.[/quote']

 

Put it back to "1". clearly there is no advange for you to leave it at "2" with your current setup.

 

There is no magic cam setting that will make everybody's car run better. This is highly dependent on the exact characteristics of your engine - here are just some of the things that effect your actual valve event timing:

 

block deck height (has it ever been milled?)

head thickness (ditto)

age of timing chain

installed height of valve in head (has the head ever been reworked?)

cam tower height (shims?)

lash pad thickness

cam grind (stock? regrind? other?)

valve lash

 

With the engine in the car, it's pretty difficult to properly degree your cam. The best you can do is to try a few different timing settings and see what works best. Nissan Motrosports sells a cam sprocket that allows adjustment for advance and retard in 3 degree increments - it's just like the stock sprocket, except it has eight timing marks/holes.

[Guest 2slo4u]

Thanks for the reply. I did get a valve job done at a local "machine shop" and he did shave the head just a hair. I asked him to shave just enough to make sure it was flat and smooth. I don't believe it was warped as I was just getting the valves and seats cut and replacing the seals. I don't think the guy put the cam followers back in the original positons, though. When I asked him if he did he said it wouldn't matter on this head. I've heard about wear patterns but it doesn't seem to show any abnormal wear so far and the clearances have stayed within spec since I reinstalled and adjusted all lash. I should have made sure to get the exact amount that was removed from the head but I'm sure he would have just made up some figure anyway.

The cam is still stock and I want to keep it that way if at all possible.

Will it cause problems if I don't shim the cam towers? I don't understand how that can cause a major effect. It would seem the valves would still open the same amount?

[TimZ]

Will it cause problems if I don't shim the cam towers? I don't understand how that can cause a major effect. It would seem the valves would still open the same amount?

It's not an issue of how much the valves open - rather it's an issue of when they open relative to the position of the piston in the bore.

 

Changing the distance between the cam centerline and the crank centerline (i.e., deck height, head thickness, cam tower shim) has basically the same effect as a stretched chain - as the distance from the cam to the crank becomes shorter, the cam timing becomes later than it would normally be (retarded). This type of error can be seen using the timing marks on the cam and thrust plate.

 

Changing the relationship between the cam and the valve (i.e., cam tower shim, cam base circle, lash pad thickness, valve installed height, etc) has the effect of changing the angle at which the rocker nominally contacts the cam lobe. This effects how early or late the cam lobe starts acting on the rocker, and can go either way (advanced or retarded). It's important to understand that this type of error cannot be detected with the timing marks on the cam and thrust plate, as these errors are introduced "after" the timing marks.

 

The timing marks are still very useful for knowing whether you are in the ballpark, but do not tell you the whole story.

 

Finally, valve lash generally has the effect of slightly changing the duration of the valve opening - as the lash gets looser the valve both opens later and closes earlier.

 

To answer your first question, unless the head/block were milled to the extent that the chain tensioner can no longer keep the chain tensioned, not having the cam towers shimmed should not hurt anything, so long as you can find a cam timing that works for you. At this point it's doubtful that you would know how much to shim the towers anyway.

[Guest 2slo4u]

Thanks for the advice again. It's good to chat with people who know what they're talking about. I learn more about my car almost every time I check out these posts. I figure the amount I donate can't even come close to the money I'll save by learning here. What an awesome site!

 

 

 

 

 

 

81turbo rusty butruns still idleshighAFTERwarmingup can'tfindvacummleaks?

[datfreak]

Ive played around with cam timing on various 4 and 6 cyl datsun motors and ive only ever made it as gutless as you are talking about by putting it a WHOLE link retarded.

There is appox 40 teeth on the top cam cog-so divide that by 360

360 divided by 40 = 9

then multiply by 2 to get crankshaft(real) measurement so you are looking at appox 18 degrees difference between teeth.. which is HUGE.

If i recall proper I think the difference between 1 , 2 and 3 is 4 degree each step .

 

Are you SURE that the cam/crank is on the correct link?

 

btw my 72 degree semi race cam is on "3" and it feels strong then when it was on "2"(or "1")

 

scott

[Clifton]

Retarding= more top end. Advancing, as you did= favors bottom end.

[Guest 2slo4u]

I like the power on the top end as I'd prefer gaining hp through rpm like the smaller newer fours do. I don't want to put undo stress on the lower internals. I did notice the lower rpm hp more when the cam was advanced, but the car is a three speed automatic and I don't like my top speed limited by the top rpm lacking.

And yes, I'm pretty sure the link positons are correct. It is back to postion 1 now and runs better.

 

 

 

Thanks for the responses. Headed to the junkyard tomorrow to get some 300zx parts to hopefully do the ecu swap. 8)