Would weak valve springs cause a backfire or sound like at misfire at higher RPM's? I hear this through the exhaust. My timing is on, as well as the distributor has been professionally rebuilt and dialed in with proper dwell. Rockers are all set at .030. The car runs strong but starts to break up at RPM's near 5000 plus. I have new wires, plugs, cap, coil, everything in the ignition circuit is new. I never checked the valve springs and the engine had less then 1000 miles on it over 17 years. I suspect tired springs, what do you think?
-
-
Re: 1965 327 Fuel Injected valve springs
Tired valve springs can certainly cause high rpm breakup and valve float, but you also should consider points if this is a non TI ign system (maybe fuelies always got K66). Duke Williams has had several posts recently on the different spring tensions on points between std and heavy duty, and the issues they cause....Craig -
Re: 1965 327 Fuel Injected valve springs
I forgot to mention that I have the NAPACS786P point set and the B28 vacuum can. When the distributo was tested I had no point float to 6700 RPM.Comment
-
Re: 1965 327 Fuel Injected valve springs
Thanks Craig, To answer your question this is a non TI car. If I replace the springs are they suppose to be the 80# type? What would be the GM part number and can I still order them from a GM dealer?Comment
-
Re: 1965 327 Fuel Injected valve springs
Jim - since you have addressed the points issue Duke raised, then the springs may be the culprit. I am no expert on the P/N's, but when Joe reads this, I know we will all find out!...CraigComment
-
Re: 1965 327 Fuel Injected valve springs
The valve springs are not high on my list. The 30-30 cam has very soft action and is not tough on springs. The springs used with SHP cams are the same as all other small blocks. Beginning in 1967 a new valve spring can into use, which is essentially the same as the earlier version, but has slightly different specs, and they are still available from GM though I don't have the part number handy.
The CS786P are standard 19-23 oz. breaker arm tension points. For engines with redlines over 5500 RPM I highly recommend the 28-32 oz. points, which would be CS7860 in the NAPA/Echlin line.
Connect a dwell meter to the car and obsever the reading while bringing the revs up to about 6000. If the dwell drops more than 2 degrees, the points are bouncing and this will cause your symptoms. The high breaker arm tension points will solve this problem if the distributor is otherwise in good condition.
Your valves are too loose! The clearance should be .026" to compensate for rocker ratio deviation from the theoretical 1.5:1. Also, the 30-30 cam requires a special adjusting procedure to ensure the cam is on the base circle while adjusting each valve. If you adjust the valves at TDC they will be WAAAY loose because the cam is on the ramp for both valves at TDC. Loose valves can bounce, and they will also pound into the seats much faster than if they are properly adjusted.
Send me and e-mail and I will return the valve adjusting procedure to you in an attached Word file.
DukeComment
-
Re: 1965 327 Fuel Injected valve springs
Jim------
There are many things that can cause the problem that your're describing. The most likely are ignition system or fuel system problems. For ignition, you might want to try a conversion to an electronic system using your existing distributor. There are several to choose from and the conversion is simple, easily reversible, and "unobtrusive".
As far as the valve springs go, if the springs are original, you wouldn't be wasting too much money replacing them. The current GM spring for your application is GM #3735381. This is the exact same spring as originally used on your engine and it's still available from GM for a list price of $7.30/each.
For high performance small block applications my favorite spring is the GM #10134358. This spring has an installed height (valve closed) pressure of 110 lbs and a rate of 358 pounds. Although it has a slightly larger-than-stock OD, it will fit in stock valve spring pockets with no machining necessary. It will solve any high rpm problems associated with valve springs. It currently GM lists for $4.36 and it's a real bargain.In Appreciation of John HinckleyComment
-
Re: 1965 327 Fuel Injected valve springs
joe, i have also used the 3927142 springs with good results on street driven small blocks with both solid and hyd lifter engines and they about 30# more seat pressureComment
-
Re: 1965 327 Fuel Injected valve springs
Clem----
The GM #3927142 have almost identical specs to the GM #10134358. However, the 10134358 are made of better material and are more durable than the 3927142.In Appreciation of John HinckleyComment
-
Re: 1965 327 Fuel Injected valve springs
Don't overlook the possibility of a short rotor in the dist, The length of the tip on the rotor was changed in the early 70's at Delco Remy (part had an "E" stamped on the flat metal side of the rotor contact) and on the high compresion engines that has been seen to cause missing above 5500 rpm. an Accel or Echlin high-performance line rotor generally will give good perfornamce.Bill Clupper #618Comment
-
Re: 1965 327 Fuel Injected valve springs
Bill, my rotor is a NAPA - RR167R. The spec sheet I received back with my rebuilt distributor is as follows: Bottom gear end play - .002/.007 Actual is .005
Centrifugal Advance/Engine RPM & Dist. Degrees
Start 920/0-2 Spec. Actual is 920/0
Maximum 2350/11-13 Spec. Actual 2350/12.5
Vacuum Advance
Inches of Hg to start 3-5 Spec. Actual 4.0
Inches of Hg. - Full Adv. 5.75-8.25 Spec. Actual 8.0
Max. degrees Advance 7.2-9.2 Spec. Actual 9.0
Dwell 30/ No point float to 6700 (Engine red line is 6200)Comment
Comment