timing mark keeps moving on race car

mike22l · 05-30-2009, 05:58 PM

I have a 3/8 dirt track race car with a 350 chev using a stock GM HEI distributor. I'm trying to set the timing and the timing mark keeps moving.
I'm trying to set total timing at 35 deg and when I rev the car up to 3000 rpm my 35 degree mark keeps moving plus and minus 5 degrees. very erratic. it has the vacuum advance disconnected but does use centrifical advance.
I am using no 1 cyl and using a 400$ snap on timing light. Could it be that the bushings are worn in the distributor? bad coil? bad module?plug wire that i'm connected to? Would a worn upper bushing cause this problem? All your thoughts please.

**wrench97** · 05-30-2009, 06:51 PM

check or tie the vacuum advance plate off to ensure it's not moving normally when in use there is vacuum to the plate which holds it steady with the vacuum line disconnected it may be vibrating at high revs and causing the erratic readings. Or to do a quick check apply some vacuum to(hand held vacuum pump or have someone suck one the line will you check) it the timing will change but if it stays steady then you'll know for sure.

mike22l · 05-30-2009, 06:55 PM

I checked the vacuum advance and it is tight. I thought that one also. Any other thoughts?

**wrench97** · 05-31-2009, 02:03 AM

The fly weights should not cause it at that rpm they would fully spun out, see it the top of the distributor shaft (where the rotor is) has play forward and backward that would be an indication of bad bushings at the top of the distributor for the rest of the bushings you'll have to pull the dist, out and check the bottom.

**pat mcgroin** · 05-31-2009, 07:54 AM

I dont know how many miles are on it but In my expierience a roving timing mark is usually a sloppy timing chain.
As stated above use a T fitting in the vacumn advance line and a vacumn guage to be certain that the vacomn is steady and check the bushings in the distributer especially the gear at the bottom.

mike22l · 05-31-2009, 07:54 AM

would worn bushings cause an erratic timing mark like i'm seeing?

mike22l · 05-31-2009, 07:56 AM

we run a gear drive so no timing chain

**wrench97** · 05-31-2009, 08:53 AM

Cam bearings would not usually do that at least not without also seeing a loss of oil pressure and maybe a knock.

**pat mcgroin** · 05-31-2009, 06:09 PM

Yes bushings in the dist. could cause some fluctuation but Im not sure how much.
Try to twist the shaft in the dist. with the flyweights off if possible but with the rotor off and the weights stationary.
See if you can tell if the gear at the bottom of the distributer has play in it.
There will be some gear backlash but see if it seems excessive.
I know it is subjective, but it is a good first test.

Without knowing the timing gear set used did it possibly include a setting for backlash
Maybe a loose gear on the front of the engine?
I'm just trying to cover the bases.

Sorry about my first post I didnt see that the vacumn advane was disconnected.

NTeyeball · 06-06-2009, 03:19 AM

No-one mentioned a worn Harmonic Balancer?
Unless you use a "solid" harmonic?

I have only ever experienced this problem via Harmonic balancer.

NT

mike22l · 07-14-2009, 08:17 PM

I found that when I advance my snap on light 2 degrees it cleans up the erratic timing mark problem. weird. I run 36 deg advance but I advanced the light 2 degrees and set the pointer on the 34 deg mark. I guess it must be my light then?

**wrench97** · 07-15-2009, 01:31 AM

Sounds like it's the light.

05-30-2009, 05:58 PM	#1 (permalink)
mike22l Registered User Join Date: May 2009 Posts: 5 OS: vista	timing mark keeps moving on race car I have a 3/8 dirt track race car with a 350 chev using a stock GM HEI distributor. I'm trying to set the timing and the timing mark keeps moving. I'm trying to set total timing at 35 deg and when I rev the car up to 3000 rpm my 35 degree mark keeps moving plus and minus 5 degrees. very erratic. it has the vacuum advance disconnected but does use centrifical advance. I am using no 1 cyl and using a 400$ snap on timing light. Could it be that the bushings are worn in the distributor? bad coil? bad module?plug wire that i'm connected to? Would a worn upper bushing cause this problem? All your thoughts please.

05-30-2009, 06:51 PM	#2 (permalink)
wrench97 Moderator, Hardware Team Join Date: May 2008 Location: S.E. Pennsylvania Posts: 18,348 OS: Win7	Re: timing mark keeps moving on race car check or tie the vacuum advance plate off to ensure it's not moving normally when in use there is vacuum to the plate which holds it steady with the vacuum line disconnected it may be vibrating at high revs and causing the erratic readings. Or to do a quick check apply some vacuum to(hand held vacuum pump or have someone suck one the line will you check) it the timing will change but if it stays steady then you'll know for sure. __________________ Power Supply and Selection

05-30-2009, 06:55 PM	#3 (permalink)
mike22l Registered User Join Date: May 2009 Posts: 5 OS: vista	Re: timing mark keeps moving on race car I checked the vacuum advance and it is tight. I thought that one also. Any other thoughts?

05-31-2009, 02:03 AM	#4 (permalink)
wrench97 Moderator, Hardware Team Join Date: May 2008 Location: S.E. Pennsylvania Posts: 18,348 OS: Win7	Re: timing mark keeps moving on race car The fly weights should not cause it at that rpm they would fully spun out, see it the top of the distributor shaft (where the rotor is) has play forward and backward that would be an indication of bad bushings at the top of the distributor for the rest of the bushings you'll have to pull the dist, out and check the bottom. __________________ Power Supply and Selection

05-31-2009, 07:54 AM	#5 (permalink)
pat mcgroin TSF Enthusiast Join Date: May 2009 Location: Toledo Oh. Posts: 550 OS: XP Professional SP2 Vista Ultimate SP2	Re: timing mark keeps moving on race car I dont know how many miles are on it but In my expierience a roving timing mark is usually a sloppy timing chain. As stated above use a T fitting in the vacumn advance line and a vacumn guage to be certain that the vacomn is steady and check the bushings in the distributer especially the gear at the bottom.

05-31-2009, 07:54 AM	#6 (permalink)
mike22l Registered User Join Date: May 2009 Posts: 5 OS: vista	Re: timing mark keeps moving on race car would worn bushings cause an erratic timing mark like i'm seeing?

05-31-2009, 07:56 AM	#7 (permalink)
mike22l Registered User Join Date: May 2009 Posts: 5 OS: vista	Re: timing mark keeps moving on race car we run a gear drive so no timing chain

05-31-2009, 08:53 AM	#8 (permalink)
wrench97 Moderator, Hardware Team Join Date: May 2008 Location: S.E. Pennsylvania Posts: 18,348 OS: Win7	Re: timing mark keeps moving on race car Cam bearings would not usually do that at least not without also seeing a loss of oil pressure and maybe a knock. __________________ Power Supply and Selection

05-31-2009, 06:09 PM	#9 (permalink)
pat mcgroin TSF Enthusiast Join Date: May 2009 Location: Toledo Oh. Posts: 550 OS: XP Professional SP2 Vista Ultimate SP2	Re: timing mark keeps moving on race car Yes bushings in the dist. could cause some fluctuation but Im not sure how much. Try to twist the shaft in the dist. with the flyweights off if possible but with the rotor off and the weights stationary. See if you can tell if the gear at the bottom of the distributer has play in it. There will be some gear backlash but see if it seems excessive. I know it is subjective, but it is a good first test. Without knowing the timing gear set used did it possibly include a setting for backlash Maybe a loose gear on the front of the engine? I'm just trying to cover the bases. Sorry about my first post I didnt see that the vacumn advane was disconnected.

06-06-2009, 03:19 AM	#10 (permalink)
NTeyeball Registered User Join Date: Feb 2008 Location: NT.Australia Posts: 49 OS: Vista Basic, XP Home SP3, Win98se	Re: timing mark keeps moving on race car No-one mentioned a worn Harmonic Balancer? Unless you use a "solid" harmonic? I have only ever experienced this problem via Harmonic balancer. NT

07-14-2009, 08:17 PM	#11 (permalink)
mike22l Registered User Join Date: May 2009 Posts: 5 OS: vista	Re: timing mark keeps moving on race car I found that when I advance my snap on light 2 degrees it cleans up the erratic timing mark problem. weird. I run 36 deg advance but I advanced the light 2 degrees and set the pointer on the 34 deg mark. I guess it must be my light then?

07-15-2009, 01:31 AM	#12 (permalink)
wrench97 Moderator, Hardware Team Join Date: May 2008 Location: S.E. Pennsylvania Posts: 18,348 OS: Win7	Re: timing mark keeps moving on race car Sounds like it's the light. __________________ Power Supply and Selection