305 V6 Engine question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Alaska_Ryan · 03-15-2010, 03:28 AM

Driving home with my 69 GMC which has a 305 V6 (yes, it is a 305 V6). The truck starts to shake, shudder and backfire horribly. I felt as though I was on an unbroken horse. I got it home and parked, but now I can't get it started again.

The engine turns over fine, but it will not catch. I have spark and gas going into the carb. I even sprayed starter fluid into the carb and nothing.

The only thing I can think is the timing chain jumped some teeth. Anyone else have any ideas or suggestions?

slorio · 03-15-2010, 09:45 AM

Alaska:
There is a good chance it is the timing chain. My two quick checks on the chain are:
First, compression test. My compression dropped from 125 lbs/cylinder to about 75 lbs./cylinder when my chain jumped. The jumping of the chain retards cam timing which hurts compression on all of the cylinders.
Second, rotate the engine at the crank back and forth with the distributor cap removed. If you have a chain loose enough to jump, you will have a lot of movement at the crank (quarter turn) before you see corresponding movement at the distributor.

These aren't definitive, but they give you a good indication of what kind of shape the chain is in. One other way if you have the equipment is to put a bore scope in where the fuel pump bolts on and have a peak at the chain. I didn't have such equipment. You can find my discussion on this in the archives at the 6066gmcguy.org website's discussion group.

I hope this is helpful. Changing out the chain is a fairly easy job on these V6's and greatly improves performance if the chain is tired.
Regards,
Steve
New Orleans

**Matt's k5** · 03-15-2010, 10:39 AM

you can check yyour firing order put number one cyl on tdc and see were your rotor points too on dist, could be your dist gear, i had this similar happen to me on my blazer but i could get it to restart but barley, found my dist came apart where the points screw on too would only go 10mph and backfiring, i know of 3 305 v6's and a 351 i never had had heard of timing chain problems these motors are ussaly bullet proof but it is possible just check all the basics , matt

68GMCCustom · 05-16-2010, 11:01 PM

...you should probably start your own... rather then derail this guys thread for your trucks issues.

...just my opinion.

dbaillargeon · 05-17-2010, 08:34 AM

Sorry to step on toes, new
to
this thought that was how it worked I
will use the thread I start. Once again I apologize to
all here

03-15-2010, 03:28 AM	#1
Alaska_Ryan Registered User Join Date: Jul 2008 Location: Delta Junction, Alaska Posts: 7	305 V6 Engine question Driving home with my 69 GMC which has a 305 V6 (yes, it is a 305 V6). The truck starts to shake, shudder and backfire horribly. I felt as though I was on an unbroken horse. I got it home and parked, but now I can't get it started again. The engine turns over fine, but it will not catch. I have spark and gas going into the carb. I even sprayed starter fluid into the carb and nothing. The only thing I can think is the timing chain jumped some teeth. Anyone else have any ideas or suggestions?

03-15-2010, 09:45 AM	#2
slorio Registered User Join Date: Sep 2006 Location: Louisiana Posts: 374	Re: 305 V6 Engine question Alaska: There is a good chance it is the timing chain. My two quick checks on the chain are: First, compression test. My compression dropped from 125 lbs/cylinder to about 75 lbs./cylinder when my chain jumped. The jumping of the chain retards cam timing which hurts compression on all of the cylinders. Second, rotate the engine at the crank back and forth with the distributor cap removed. If you have a chain loose enough to jump, you will have a lot of movement at the crank (quarter turn) before you see corresponding movement at the distributor. These aren't definitive, but they give you a good indication of what kind of shape the chain is in. One other way if you have the equipment is to put a bore scope in where the fuel pump bolts on and have a peak at the chain. I didn't have such equipment. You can find my discussion on this in the archives at the 6066gmcguy.org website's discussion group. I hope this is helpful. Changing out the chain is a fairly easy job on these V6's and greatly improves performance if the chain is tired. Regards, Steve New Orleans

03-15-2010, 10:39 AM	#3
Matt's k5 BLAZER THIRTY!! Join Date: May 2007 Location: Utah Posts: 324	Re: 305 V6 Engine question you can check yyour firing order put number one cyl on tdc and see were your rotor points too on dist, could be your dist gear, i had this similar happen to me on my blazer but i could get it to restart but barley, found my dist came apart where the points screw on too would only go 10mph and backfiring, i know of 3 305 v6's and a 351 i never had had heard of timing chain problems these motors are ussaly bullet proof but it is possible just check all the basics , matt __________________ 49 chevy 5 window 20 year project (sold)😟 57 ford fairlane (dad's car never got to it before he passed away R.I.P I LOVE YOU DAD.) 62 GMC 305 V6 custom L/B 72 HIGHLANDER K5 BLAZER 2nd owner 71 K5 MAMMA'S RIDE! 63 GMC 4X4 305 V6 62 GMC SHORT BED SERVICE BODY V6 (STUMPY) 74 GMC CUSTOM 1500 L/B

05-16-2010, 11:01 PM	#4
68GMCCustom Truck and auto performance nut Join Date: Feb 2007 Location: McKinney,Texas Posts: 3,848	Re: 305 V6 Engine question ...you should probably start your own... rather then derail this guys thread for your trucks issues. ...just my opinion. __________________ Kurt - '68 GMC short step - NIB '09 LY6 6.0L crate motor w/mods, NIB '12 crate 4L85e w/billet 3k stall Circle D, 3.73 posi 12 bolt, DynaTech f-swap headers, 3/4 drop, handling mods, etc. - my toy '72 Chevy LWB C-10 Highlander - 350/350 ps/pb/tilt/ac - not original but close '06 Chevy TrailBlazerSS - LS2/4L70e - little black hot rod SUV - my DD '18 Kia Sorento - wife's econo-driver '95 Chevy S10 - reg cab shortbed, LS, 4.3, auto... my '68's powertrain and chassis build -links broken A surprise phase - carb to efi -links broken Last edited by 68GMCCustom; 05-16-2010 at 11:02 PM.

05-17-2010, 08:34 AM	#5
dbaillargeon Registered User Join Date: May 2010 Location: massena NY Posts: 33	Re: 305 V6 Engine question Sorry to step on toes, new to this thought that was how it worked I will use the thread I start. Once again I apologize to all here __________________ A lot to think about, not much to worry about...



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