setting timing w/ shaved head?

[88accordSF]

in my general paranoia of engine detonation, i noticed that with my new head installed, with the timing set exactly on the factory mark (15 degrees, at the red timing line, automatic, in D gear, with the handbrake engaged), i ~think~ i'm getting just a bit of ping when going up low-angle hills on the highway. i've been upshifting to counteract this detonation. i generally run 87 octane gas.

which would bring me to think...

possibly the new head, i got was shaved quite a bit? therefore raising the compression just a bit?

so in order NOT to have to buy 91 gas, i'm going to set the timing at 13 degrees instead... just to keep the engine from detonation... i'd rather run a bit on the safe side, considering i drive this car pretty slow anyways

anybody else encounter this?

or am i smoking too much of that pot that we're all discussing in the thread .... :bong:


...also, i'm assuming that the 2 timing marks on either side of my drive plate (auto tranny) for the timing light are 2 degree either way from 15, so that would be 13 and 17 degrees, respectively. is this correct? basing this off the service manual "15 +/- 2" text....

[2oodoor]

as your motor wears slowly, and with a few resurfacing of the head.. you no longer use factory ign timing specs anyway, it just gets you in the ballpark. You will have to drive it and set it two or so degrees at a time until you dont ping.
You should check other things too, are you leaning out cause the fuel filter or in tank strainer is restricted? is your egr functioning correctly? what plugs are you using? When you cut the head, you put the cam closer to the crank so,valve timing is affected after a certain point. You have to get it close and compensate the drivability with ign timing adjustments.
Also check your centrifigal advance wieghts in the bottom of the distributor, they could be stuck out, or in. affecting you timing curve.
This is a good excuse to get an adjustable cam gear, it can let you acheive the original spec even though the head is now too short.. lol

[88accordSF]

----are you leaning out cause the fuel filter or in tank strainer is restricted?----

both fuel filters replaced. should check the in-tank strainer, good idea.

---is your egr functioning correctly?----

i'll need to check the master manual and check that

----what plugs are you using?-----

NGK BRP6EIX-11 Iridium plugs


----check your centrifigal advance wieghts in the bottom of the distributor----

just threw in a Vapex Hitachi Distributor from Napa auto store a couple months ago. should be good, but i'll check on those.


----This is a good excuse to get an adjustable cam gear, it can let you acheive the original spec even though the head is now too short---

i was talking about this EXACT subject with Messy last night while hangin out downtown...

currently trying to visualize the difference between adjusting the distributor timing, and adjusting an adjustable cam gear would be..... the first one sets the spark timing, whereas the second one actually sets the timing of the valvetrain opening and closing in relation to the spinning of the crank (i think?)

i think your right Roodoo (and Messy).... may need to grab an adjustable cam gear to get that valvetrain perfectly synced up to the bottom end.

the next question would be, whats the best way to determine exactly how much my head is OFF factory spec by, in terms of the amount of aluminum milled off from the head work? i could set the engine to factory timing, and then adjust the cam gear as needed to avoid detonation (after confirming that fuel delivery & intake stuff is all on point)?

[cygnus x-1]

When you mill the head though the cam (and therefore the distributor) are slightly retarded with respect to the crank. And the change is pretty small so I don't think this is the cause of the detonation. Unless you have to seriously back off the ignition timing to correct it I wouldn't worry about it. If you use 91 octane fuel will the pinging stop?

C|

[2oodoor]

I agree with cygnus, I use premium in the Accord because the head is shaved quite a bit. It also helps me keep it in tune with enviornmental and weather changes.. the Webers are just a little particular sometimes with the air mix.
They are mixing so much garbage in the general fuel stock nowdays, regular fuel is a crap shoot but if you have a modern FI car those are usually engineered with knock sensors that retard the timing.

[cygnus x-1]

To elaborate some more:

Ignition timing is not an exact science because there are so many factors that affect how an engine runs. Fuel quality, environmental conditions (temp, humidity, atmospheric pressure), engine mechanical geometry (displacement, combustion chamber volume, exhaust setup, intake setup, valve timing, etc.), driver expectations (fuel economy, power, etc.), the list is huge. The manufacturers numbers are generally just a guideline to get the best compromise between economy, power, and reliability. You can deviate from the factory settings as long as you understand what effect your deviation will have. If you run under hot conditions and have pinging you may need to back off the timing and/or run higher octane fuel. If you want more power and are willing to run premium fuel you can bump the timing up. The old school way to adjust timing is to start at some known good value and then advance the timing by 1 or 2 degrees and do a test drive. If it pings back off 1 or 2 degrees until the pinging stops. Then it's good. If it doesn't ping advance it a little more and test drive again. Keep doing this until you get to a point where it just barely DOESN'T ping.

So if it doesn't ping with better fuel then it's probably pretty close and just needs to be backed off a touch to work with that-stuff-that-passes-for-fuel these days.

C|

[88accordSF]

i'll back it down to 13 degrees and see what happens

[g.frost]

Ok, I can't be any help and glad that others could, but no one else mentioned it: I can't help thinking of you with a timing light and a real close cut, fresh polished head haircut. It should work but maybe wear a hat if it's sunny.

[2oodoor]

Ok, I can't be any help and glad that others could, but no one else mentioned it: I can't help thinking of you with a timing light and a real close cut, fresh polished head haircut. It should work but maybe wear a hat if it's sunny.
timing marks on these cars is on the flywheel so there are no moving parts, hair grabbers.. lol

[AZmike]

Leaving the timing advanced and running premium doesn't necessarily cost extra. I've found that I consistently get slightly better fuel economy running with somewhat advanced timing and high enough octane to prevent detonation. I pay 5-10% more for the fuel and get 5-10% more miles out of it.

Why not give it a try? Given what fuel costs now another $0.20/gal isn't really much more money.

[88Accord-DX]

There are a lot of variables in timing with a shaved head. The most part of it, is how much the head is shaved. Most OHC design engines have a 1 degree advance cam timing to .012" milled off the head. Adjustable cam gear can restore it. Or drill out the bolt holes on the dizzy for more room to work with.
With most interference OHC design engines, if you milled the head more than specifications, a shim should be used to restore it back to specs. Ping is what will kill you. Watch out for piston to valve contact on interference design OHC blocks. Replaced a few bent valves from a tooth off the cam sprocket.

[88accordSF]

There are a lot of variables in timing with a shaved head. The most part of it, is how much the head is shaved. Most OHC design engines have a 1 degree advance cam timing to .012" milled off the head. Adjustable cam gear can restore it. Or drill out the bolt holes on the dizzy for more room to work with.
With most interference OHC design engines, if you milled the head more than specifications, a shim should be used to restore it back to specs. Ping is what will kill you. Watch out for piston to valve contact on interference design OHC blocks. Replaced a few bent valves from a tooth off the cam sprocket.

i used a graphite head gasket that was included with the head that i ordered... not sure if that was a stock spec or slightly thinner.

do you happen to have a source on that shim?

bought the head from engine shop on the east coast, not sure exactly how much was shaved off....

[88Accord-DX]

I haven't shimmed an A20A1 or A20A3 block before, but I can find out through Napa if they have one though. Post a result Monday.

[2oodoor]

if if you just reset redo the t belt then reset dist its easier than redoing head gskt
pull all plugs out to spin motor by hand & look in hole to see piston & also feel if vlve contacts
they wouldnt sell a head cut too much id hope
mine is cut appx .028 prob more , no clearance issues just cam timing ....not 4 long heeheee