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New engine rebuild timing Q
https://slantsix.org/forum/viewtopic.php?t=62485		 Page 1 of 5
Author:  wjajr [ Sat Jun 16, 2018 8:14 am ]
Post subject:  New engine rebuild timing Q
New thread same engine just rebuilt & installed

The particulars:

225ci
bore 3.440
Cam; Oregon grind 346
lobe separation 108*, tappet @.050" I=.234" E=.228"
Intake open 13* BTDC close 41* ABDC
Exhaust open 46*, close 2*

Lift at valve INT= .476 Exh = .479

Harmonic balance timing mark at 1000 rpm idle is 1.5" past 10*BTDC This is where engine reaches fastest idle and highest vacuum ~13Hg.

When engine is shut down there is no longer back peddling run-on, it just stops. Happy, happy, happy.

Went for some fresh gas this morning after about a half house of tuning idle air (holley 390) screws out 1.5 turns and very sensitive to 1/8 turn in or out, and no rich exhaust stink. Best that thing has worked in ten years I have had it. Trip to station about a mile and a half, 40 mph limit, and umped in some Sunoco 93.

On the trip to station short WOT I thought I heard some serious knocking, was burning 7 month old Sunoco 89.

After fill up engine had a hard time turning over very tight. After five minutes of cooling (hood still is off), it was able to turn over fast enough to start, and ran well. Would this be due to fresh tight engine getting hot? I think battery was fully charged. This same occurrence happen yesterday after brake-in, and some rough tuning and transmission top-off.

After driving into garage from gas station, it idled down to 850 rpm in gear and died; (I have set idle at 1000 rpm in park).

When I was trying to fire engine for first time after rebuild, timing mark aligned to between 0 & 10*BTDC when #1 was top of compression stroke checked by feeling piston top with small screwdriver. It would not start at that setting. Distributor need to be rotated counter clock-ways so vacuum can was pointing to 3 o'clock before engine would start; that was after I dumped some varnish smelling fuel from carb, and primed with fresh.

Distributor has been recurved so no mechanical advance is added until 1500 rpm is reached, and is all in at 2800 rpm.

Do I have the wrong harmonic balance, or is cam installed incorrectly, or is my addled atrophied brain messing with me again?

After sitting here thinking about spark knock or whatever I thought I heard, it may have been sound of flopping hood hinges knocking around in open position. On way back from station less knocking was to be heard.
Author:  DadTruck [ Sat Jun 16, 2018 10:37 am ]
Post subject:  Re: New engine rebuild timing Q
With #1 piston at TDC and on the firing stroke, both the intake and exhaust valves should be on the heel of the cam and have play between the rocker arm tip and valve stem,,,the timing mark on the damper should align with the 0 on the timing tab.
It is always best to verify the damper-timing tab relationship before installing the head, then you can use a top dead center tool or depth micrometer to set #1 exactly at TDC.
You can also use a Piston Stop with the head installed, it is more involved.
Author:  wjajr [ Sat Jun 16, 2018 5:59 pm ]
Post subject:  Re: New engine rebuild timing Q
I had the engine builder assemble engine. He said he degreed it and was off, I think he said, 4*, and didn't take the time to install eccentric or whatever is used to fine tune cam position to dial it in. I wasn't pleased when he told me that as it was loaded onto the truck to bring home. Engine is gutless in low rpm, comes to life past 3000 rpm.

Yes, when piston is TDC both rockers are free to move, and mark on harmonic balancer alignes with 0* mark or very close. I haven't stuck a piston stop in plug hole and rotate engine back & forth to locate true TDC, to timing markings.

The point is, mark on balancer is 30+* by eye BTDC for engine to start idle and run. With old cam & balancer I had initial timing set at 15*. None of this is making any sense to me
Author:  DusterIdiot [ Sat Jun 16, 2018 6:45 pm ]
Post subject:  Re: New engine rebuild timing Q
Quote:
Engine is gutless in low rpm, comes to life past 3000 rpm.
That's a sure sign that the cam is retarded...(it can also be a sign that the cam is really big for the compression ratio... which it is not, in this case).

If your static or initial is 30 (a tooth off or better on the dizzy), that's also a sign that the fire needs to be lit realllllly early to make up for the valve events being late....

About now, I would be getting a piston stop and draining the radiator, so I could get a degree wheel on the crank
and see how far off it is.... If it is off, it will be very involved to drain the block and pull the timing cover to make
things right and put it all back together again (done that a few times and loathe to do it again...)...

Not sure if your engine assembler will do things right and credit you back for the time and material to fix his obvious
goof up... or fix it himself as it shows he's not professional enough to do a good job especially when installing a cam
in a performance application no matter what the make... (even though I have a couple of very good machinists
that would do this correctly and know cam theory and why it's done that way, it's still a reason that I like to assemble
my own builds and degree my own cam)...

Sad to hear you have to deal with this...
Author:  wjajr [ Sun Jun 17, 2018 1:14 pm ]
Post subject:  Re: New engine rebuild timing Q
Between Father's day, visiting my 96 year old Dad at Veteran's home, and getting ready for a cook out, the piston stop was employed. Luck was on my side as first stop landed on 0* mark,center of tab, second stop landed on what would be 12* ATDC, so center line between the two, or actual TDC is at 6* ATDC mark on timing tab.

Piston at TDC places rotor pointing between 4 & 5 o'clock looking down at distributor.

Does the cam need to be advanced 6* using bushings or eccentric devices?
Author:  DusterIdiot [ Sun Jun 17, 2018 3:16 pm ]
Post subject:  Re: New engine rebuild timing Q
Quote:
Does the cam need to be advanced 6* using bushings or eccentric devices?
You will need to look at the cam lobe to crank reference using a degree wheel... we now know the damper mark is 6 ATDC when the piston is at TDC...
so when you set your timing you will want to mark the tab in that location with some whiteout/paint so you know which mark to use to set proper timing..
The degree wheel with help of a dial gauge and stand will see where the cam really is at...

Depending on what you find you may need to drill the cam gear and install a bushing, or you may get lucky and the cam gear may just need a nudge one tooth
advanced to be "good enough" (divide 360 by the gear teeth and you may only need to advance the cam gear a tooth to get a 7 or so degree advance on
the intake lobe centerline).
Author:  Charrlie_S [ Sun Jun 17, 2018 3:56 pm ]
Post subject:  Re: New engine rebuild timing Q
Quote:
Piston at TDC places rotor pointing between 4 & 5 o'clock looking down at distributor.
Has nothing to do with where the cam center line is located.
Author:  wjajr [ Sun Jun 17, 2018 5:06 pm ]
Post subject:  Re: New engine rebuild timing Q
Ok Thanks

I can't get back to this until Monday afternoon.
Author:  wjajr [ Tue Jun 19, 2018 2:01 pm ]
Post subject:  Re: New engine rebuild timing Q
As of yet I have not put the degree wheel on.

Now that I know TDC is indicated on timing tab as 12 ATDC, static timing is now set at 16* BTDC, Idle in park is 1000 rpm at this setting, vacuum is 7 Hg. I have to feather the throttle when in gear at idle, rpm drops to 700 and to lower rpm headed for a stall. The idle mixture screws now out 1 3/4 turns. Engine wants and likes more advance at idle, rpm goes up quickly past 16 BTDC as I think mechanical advance kicks in. I thinking a heaver spring to hold back mechanical advance to 1600 rpm may help. In the past often engine would not idle down after a long trip, and suspect that light spring not fully pulling in governor weights.

My notes from last recurve list mechanical advance kicking in at 1400 rpm with short black spring which may now start advance closer to 1200 rpm, the other spring is long slot stiff black mechanical all in at 2800.

After idling engine for 20 to 30 minutes temperature needle was pointing just right of the "P" on gauge; thermostat is still removed. Would this be from engine being tight.

I'm still have a valve hanging up causing an occasional fuph that is coming from one of the back three. Will some road time help fix that?

Wouldn't slacking off the lash help idle, it is still at cam grinder's .012" both I & EXH? Where I can't get engine to idle down and stay running, I haven't attempted a hot lash. Any rpm over 500 during a lash sprays oil all over the windshield, freshly detailed engine, inner fender, and floor.

02 sensor shows rich while idling, but exhaust dosen't make that rich stink like it did before rebuild, makes me think idle mix is close enough for now.
Author:  DusterIdiot [ Tue Jun 19, 2018 5:17 pm ]
Post subject:  Re: New engine rebuild timing Q
Quote:
As of yet I have not put the degree wheel on.
This is the single most important item... your valve timing is late and you are losing your low end power as the intake valve is closing during the compression stroke
not before, and now you've tuned everything to try and band-aid the critical issue. Get this done first, you can't make up for a retarded cam no matter how much tuning
is done to the ignition timing or valve lash, or carb settings...

7" of vacuum is horrid for this cam it should be double that... the good news is that the engine will work great above 3000 rpm, and you won't
have to worry about NOx emissions as much...and a stock 1 barrel engine will have more torque at idle than your current build up to 2000 rpm...

:?
Author:  Dart270 [ Wed Jun 20, 2018 3:28 am ]
Post subject:  Re: New engine rebuild timing Q
I thought you said 13" Hg at idle earlier? That is about right for this cam. Although, I agree that getting the cam timing right will make it better down low. This combo will really like 15 deg or a bit more timing at idle. 10-12 is not enough. Narrowing up the slots in the dist is likely needed.

Lou
Author:  wjajr [ Wed Jun 20, 2018 4:55 am ]
Post subject:  Re: New engine rebuild timing Q
That higher idle vacuum was with timing +25*, but it would fart back up through carb and stall then not turn over fast enough to start until it cooled down a bit.

This is why I had an engine guy do the assembly, because I didn't feel confident doing the job on my own. No mentors handy nearby to guide me using the wheel.

I'm going to call shop that did the engine this morning, and discuss making the job right.
Author:  Dart270 [ Wed Jun 20, 2018 7:13 am ]
Post subject:  Re: New engine rebuild timing Q
OK, 25 deg is too much. Cam timing correction should help. Best to drill the cam gear locator pin hole to 3/8" and get the std Chevy cam bushings (summitracing, cheap) to do advancing.

Again, you should be setting the cam at 100 deg installed intake valve centerline. Do not let anyone tell you different or try to talk you out of this. 98-101 should be the acceptable range. Many, many Slant 6ers who know what is going on have used this setting successfully. Screw the Chevy/V8 guys "wisdom".

Lou
Author:  wjajr [ Wed Jun 20, 2018 10:13 am ]
Post subject:  Re: New engine rebuild timing Q
I have to get my head wrapped around which way intake lobe center line advance is from cam card's list of 104*. By setting lobe center line at 100* that would be advancing 4 degrees, right?

It's time to view a few You tubes, and do some reading.
Author:  Dart270 [ Wed Jun 20, 2018 11:57 am ]
Post subject:  Re: New engine rebuild timing Q
If the cam was ground with 104 as the intake centerline, then yes you should advance 4 deg. Lobe separation angle and installed centerline are completely different cam spec numbers, BTW. That cam should have LSA of 106, if it is the standard Oregon grind.

Lou
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