Valve Clatter - Timing ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

TC70C10 · 04-30-2003, 01:00 PM

I hear some valve clatter when it hit 2nd and third gear on a slight incline on my 305 K5 Blazer. I've bumped the timing from 4 to 8 to 12 without major improvement although 12 does sound better than 8 degrees. Yesterday I filled up with 89 octane to give it a try. Again some improvement. This is a newly rebuilt motor with about 2500 miles on it.

Ideas.

rockman20 · 04-30-2003, 02:30 PM

Just to rule out the obvious, you have adjusted the valves correct?

TC70C10 · 04-30-2003, 03:31 PM

To be honest, the valve adjustment crossed my mind but I haven't done it yet. I really thought it was the timing. Thought I'd hear valve clatter all the time if they needed adjusted.

I can't remember adjusting the valves after installing the 350 in the 70 C-10.

Also, this was a motor swap not a motor I rebuilt.

**swervin ervin** · 04-30-2003, 05:24 PM

Is it valve clatter or spark knock you are hearing? By your description, sounds like spark knock to me. Try lowering your timing to 6 BTDC and check it. 305's are the worst engines ever built by GM for this. The 305 combustion chamber was the cause. This is the very reason GM used the ESC distributors with knock sensors in LE9 trucks.

04-30-2003, 01:00 PM	#1
TC70C10 Registered User Join Date: Nov 2001 Location: Harvest, AL 35749 Posts: 337	Valve Clatter - Timing ? I hear some valve clatter when it hit 2nd and third gear on a slight incline on my 305 K5 Blazer. I've bumped the timing from 4 to 8 to 12 without major improvement although 12 does sound better than 8 degrees. Yesterday I filled up with 89 octane to give it a try. Again some improvement. This is a newly rebuilt motor with about 2500 miles on it. Ideas. __________________ 1981 K5 Blazer 305, 4spd, 4x4, 4" Lift, custom bumpers, Warn 9.5 Ti Winch 1995 T10 Blazer 4.3L 4x4 (Son's) 2004 GMC Envoy 4.2L 2WD 2005 GMC Sierra Crew Cab Z71 4x4 5.3L 240 Fun Finder Travel Trailer Harvest, AL 35749

04-30-2003, 02:30 PM	#2
rockman20 "The dude abides" Join Date: Apr 2003 Location: North Dakota Posts: 472	Just to rule out the obvious, you have adjusted the valves correct? __________________ RockMan 1993 Chevy Silverado C3500 1 ton dually 1994 Honda Civic 1969 Oldsmobile Cutlass S 1953 IH Farmall Super M New to the fleet: 1992 Subaru Loyal

04-30-2003, 03:31 PM	#3
TC70C10 Registered User Join Date: Nov 2001 Location: Harvest, AL 35749 Posts: 337	To be honest, the valve adjustment crossed my mind but I haven't done it yet. I really thought it was the timing. Thought I'd hear valve clatter all the time if they needed adjusted. I can't remember adjusting the valves after installing the 350 in the 70 C-10. Also, this was a motor swap not a motor I rebuilt. __________________ 1981 K5 Blazer 305, 4spd, 4x4, 4" Lift, custom bumpers, Warn 9.5 Ti Winch 1995 T10 Blazer 4.3L 4x4 (Son's) 2004 GMC Envoy 4.2L 2WD 2005 GMC Sierra Crew Cab Z71 4x4 5.3L 240 Fun Finder Travel Trailer Harvest, AL 35749

04-30-2003, 05:24 PM	#4
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Is it valve clatter or spark knock you are hearing? By your description, sounds like spark knock to me. Try lowering your timing to 6 BTDC and check it. 305's are the worst engines ever built by GM for this. The 305 combustion chamber was the cause. This is the very reason GM used the ESC distributors with knock sensors in LE9 trucks. __________________ Mike 1985 Chevy C-10



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