jonbill

I think the curve goes flat because that's the best you can do reliably with springs and weights and centrifugal force. Electronic systems may reduce advance after the initial peak as the engine gets up to peak torque and then increase again afterwards.

Yep, if you only pay attention to the interest of having peak gas pressure at 22 ATDC, you would keep advancing the timing forever. But there are competing interests. First, although the combustion takes a reasonably constant time, that combustion doesn't proceed linearly. It starts slow with a small flame front and grows and gets faster. Second, keep this in mind: gas pressure when the piston is on the way down is good. gas pressure when the piston is on the way up is bad. At 1000rpm with 15 deg advance, the 1.3 ms of combustion takes 37 degrees of crank rotation. 15 BTDC and 22 ATDC (say). most of the burn and and nearly all the gas pressure happens when the piston has passed TDC (ATDC). At say 5000 rpm, the engine is going 5x faster but the combustion still takes 1.3ms. So you need 5x more degrees of rotation to give time for that 1.3ms burn. So we need 5x37=185 degrees for that 1.3ms. If it is to complete at 22 ATDC then it has to start at 163 degrees before TDC. So now nearly 90% of the combustion and a lot of the gas pressure happens before TDC, while the piston is still on the way up. So although peak pressure will still come at 22 ATDC, very significant pressure has happened while the piston is rising, which slows it and will cause some of the fuel mixture to explode. (detonation) so the negative impact of so much gas pressure before TDC outweighs the value of having peak pressure at 22 ATDC. Caveat: I am guessing at the causes and science here (although the article zedhead posted seems to agree with me) . But.. I am sure it is impirical fact that there is no more power to find by having more advance than that approx 35 number, and actually you get a broken engine instead through detonation.

The combustion is happening both sides of TDC. With low engine rpm, most of the combustion and gas expansion happens on the downside after TDC. As engine speed goes up, in order to keep peak pressure at 22 ATDC, more and more of the gas expansion has to happen on the upside, before TDC. Somewhere around 2500 to 3000 rpm the benefits of increasing advance and the downside of increasing combustion before TDC cross over and so Nissan (and everyone else) decided to limit the mechanical advance at that engine speed. Imagine the ignition has been advanced to 80 deg BTDC at 6000 rpm. (I'm just guessing at numbers!) combustion had to complete between 80 BTDC and 22 ATDC. That means approx 80% of combustion has happened before TDC, and that's a lot of gas pressure trying to stop the piston from coming up, and the gas is under very high pressure and any remaining fuel mixture is going to detonate. So you get serious knock and lots of heat but no more power. Something like that anyway :)

The Internet has come on quite a lot since 2002.

The purpose of firing the spark before TDC is to get max cylinder pressure at the optimum point - I believe I read that the maths works out at about 22 deg ATDC is the optimum point. If combustion was instant, then 22 ATDC would be the spark timing, but combustion takes time and so the ignition is started at the appropriate time before hand. Since the speed of combustion is reasonably constant, as engine speed goes up, you have to start ignition earlier. I.e as the engine goes faster, you need more degrees of rotation for the time it take for combustion to reach its peak at 22 ATDC. So that's why the advance curve is set to give about 15-20 advance at idle and 30-35 at 3000 rpm. The question then is, why not keep advancing the ignition timing after that? The speed of combustion is still pretty constant and the engine is getting faster.... And I think the answer is something to do with by the time you're igniting at much more than 35 BTDC, the amount of cylinder pressure you've developed while the piston is still rising becomes significant and a problem (detonation) , so you have to compromise and accept that peak pressure must come increasingly after 22 ATDC as the engine speeds go up beyond that.

Thanks, I think that's the same pic I saw above - honestly, I can't see anything unusual. It looks like my distributor cap to me.

Can you highlight where in the pics it shows the grinding? I can't see it. Also a sound recording might be good. One man's grinding is another man's whirring!

No. The valves that seal compression are in the head, not in the manifolds.

Yep, big step up from changing a manifold gasket to changing the head gasket. Not the sort of thing to do as a "while I'm there" if there's no problem and you're not so confident.

I'd go colourtune too. I'd guess you have an air leak at #6.

I'd take a long nose 4.11 R200 at that price, if that's what it is.

Yes it should be at about 14v if the alternator is working. If the alternator is related to the low idle it might be that the alternator is putting a lot of load on the engine. Try disconnecting the belt and see how hard it is to turn the alternator by hand.

Well done. I think you've dodged a bullet.

https://www.eurodns.com/whois-search/deals-domain-name I put the domain name in there and it gives you some details of who registered it. There are other similar services around.

And forumtrike-talk.com and aussies-deals.net are both registered to the same person in Yuma AZ.

Eautosmart.com is registered to an individual (not a company) in Moscow, Russia.

I'd runaway. Look at this. Apparently a review of eautosmart on an Australian review site. http://www.aussie-deals.net/aussies-deals/motor-vehicle-america-review/eAutoSmart%20Traders-index-thread-FFgret555.html But theres nothing else on the site at all. The root redirects to the eautosmart review. If they're not scam outfit, they're not averse to dodgy marketing practices. Same here. https://forumtrike-talk.com/trike-talk/forum/threads/are-safe-to-use-eAutoSmart%20Traders-thread-VV5464WZZ.html Run.

If you get piston #1 at the top, and both cylinder 1 cam lobes are symmetrically up, then you're at tdc between compression and power strokes and you can time the distributor spindle.

The dizzy and the cam sprocket can never tell you where TDC is. You can buy or make a tool like this to find tdc, https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F192244689624 then make a pointer to record it. You don't need to worry about cam position etc. Tdc is tdc, twice a cycle.

Looks spot-on to me.

I'm pretty sure that will depend on the ecu. I'm confident my Speeduino would be happy with a cam sensor signal at the same time as the crank sensor getting the missing tooth.

I have a Speeduino with a crank damper trigger wheel, wasted spark and GM 6 cylinder coil pack, but it could work with COP. Cheap and effective.

Just checking : you know cam timing is completely independent of ignition timing, right? It's just you mentioned adjusting cam timing after talking about ignition timing problems.

I used a zx distributor with my stock 74 tachometer. Lots and lots of people have zx distributor with stock tachometers and no problems I think. I'm inclined to suggest try a different stock tacho before a different distributor. Maybe there's a problem with your tacho.

Nice camera work! Some of the nicks look like casting flaws, some look like impact damage. Agree nothing to worry about.