I've got this little knock/ping problem with my a14 datto motor. I only noticed i had a problem after i bought myself a timing light. After checking my timing I got quite a shock cause my timing was set to 5 degrees ATDC I though to myself well this explains allot and set it to 5 deg BTDC. Only to discover that if my timing is set to where it is suppose to be I experience some major knock under the slightest throttle.

So i set my timing to TDC in the hoped that it'll be drivable, and it is, up until the point where the engine heats up properly then the lovely sound of destruction returns

At this point I was pretty sure that it was carbon on the sparkplugs(cleaned them and no change) or in the combustion chamber but another factor came into play. I bought a pressure tester just to make sure that its not the compression that's to high. The results are scary, I got an average pressure of 1425kPa on each cylinder and its suppose to be 1245kPa .

So, if my compression is too high won't it knock when the engine is cold as well?
If I need to drop the compression using a copper gasket, how do i work out how thick it must be?

its not very common for compression to just jump up like that.

anyway. try fiddling with your timing a bit more. try it at like 10deg btdc and then at 15 and see if that helps.

dropping the compression is most easily done by using a thicker head gasket (as you suggested).
anywhere above 1mm thicker than the 1 you have now should drop it down a factor of 1, from 10:1 to 9:1 say (9:1 is standard).
but id recommend advancing the timing more first.

also try it without the vacuum advace disconnected. it may be faulty and causing your timing to retard or something...

Hi Losadel

Happy to see another South African on this site, but sad to hear about your problem.

I personally would do the following:
1. Check to see if your distributor is not in the wrong place. Meaning, one tooth out.
2. Talk to a Nissan mechanic about your comp on the comp gauge.
3. Can't you talk to the previous owner of the bakkie to find out if he fiddled with the cylinder head?

If your comp is too high, you can let Payon make a custom thicker head gasket.
A mechanic I normally talk to and use specialize in BMW's. Because the cylinder heads of these cars are so expensive he use thicker head gaskets when needed.
He showed me a BMW in his shop that he used a 3mm thicker than standard head gasket without blowing head gasket problems.
Or you can buy a second hand cylinder head from a scrapyard that is still in good condition.
First play with your distributor and timing to make sure before going through all the trouble.

check what fuel you are running, should be 96 octane or above, and double check to make sure the TDC mark on the crank pulley is correct.

LOL, Ronald, maybe its something like variable valve timing but only with compression . I'll fiddle some more with the timing tonight. It'll be nice not to have to pull the cylinder head.

Hey 1200GXman. I've checked the distributor and its in the right place. Unfortunetely the previous owner is M.I.A. but I do know the head has been skimmed atleast twice ( was rebuilt before I bought it and I blew the topgasket ).

dattodevil: I'm running 95LRP, i've added some octane booster to the mix but that seemed to do very little if anything at all.

Hi Losadel.
That octane boosters are Bull$hit.
I have tried them in the past on my other ride that also has a ping when it becomes very hot and I drive it hard.
(Volkswagen citi golf CTI)
It did'nt help at all.

I may be wrong but I think your cylinder head is skimmed past max.
If you decide to replace head gasket with a thicker one, cc each chamber on your cylinder head to see if they are all more or less same cc's.

Quote: So with the timing set at an 'indicated' 5 degrees retarded, it didn't ping. At TDC, it pings when it's hot. At 5 degrees advance, it pings a lot, so it looks like we have a pattern here & I would recomend against setting it at 10 & 15 degrees advance as it doesn't take Einstein to figure out the probable result.

Dattodevil is correct, so lets get back to basics. How do you know that the piston is actually at TDC when the timing mark lines up. Best to pull the plugs & slip a cane chopstick down number 1 plug hole & turn the crank very slowly with a long bar & socket while holding the chopstick gently in your fingers.
You will soon get to figure out when the piston is at TDC. This is not 100% accurate of course, but do your best, & if the mark is way off, then that could be a problem & a small dab of white paint to make a new TDC mark would be a good idea.
If the existing mark is accurate, then it's time to look for other causes, but make sure that this is right first.

The default position for the vacuum canister is in the non-advance position & it only advances when you are at light throttle, so at worst, it will remain in the 'at-rest' position & not provide any vacuum advance at all, even when faulty.

That octane boosters are Bull$hit. *phew* I didn't want to say it out loud but i figured as much

I've checked my TDC marker and it was difinitly accurate or very close to accurate. I actually used the same method as you Dodgeman, only I thought I was really clever at the time when I thought of it

I think my distributors advance spring mightof stretched a bit causing it to advance to much. If its not that i'm going to throw in some warmer sparkplugs and see if that doesn't help aswell.

TA

Losadel

Let us know what solved your problem if you get a solution. I am very curious.
Did you check your air/fuel ratio?
Maybe your carb is set too lean.

But I still think your cylinder head is skimmed too much.

Quote:

Einstein is dead. I'm pretty sure he wouldn't feel up to playing "find out whats wrong with the engine" today.

plus i only SUGGESTED he try the timing at different advances. and if he did discover what you suggested and that it would knock more, at least we know for sure. can't be sure until you've tried it....