February
2
2012
HOW TO REPAIR COOLANT LEAKS AT THE CORE PLUGS ON INLET MANIFOLDS
December
22
2011
This is a picture of the drivers side of a Chevy 261 truck engine. We have added some text to identify different items of interest. (CLICK PICTURE FOR FULL VIEW)
November
26
2010
The most frequent complaint I hear is from people who complain that since they’ve installed their multiple carbs, the engine hesitates and stumbles at low speed on initial acceleration even after warm-up. The most blamed culprit is the darn Rochester Carburetor. Usually it is falsely accused!
Usually while installing dual exhaust manifolds or headers, the production exhaust heat supply to the inlet manifold is eliminated because (except Edmunds Inlet Manifolds and Clifford’s) there is no provision or instructions to provide heat…Why?? I don’t know and could only guess. In any event heat will be required to achieve good driving response and reasonable fuel economy. Here’s why;
As liquid fuel enters the manifold from the carburetor, the vacuum vaporizes the fuel and causes a chilling effect on the walls of the manifold much like the chilling effect of spraying an aerosol on your skin. Now you have a cold manifold. If you do not have a continuous supply of heat the manifold will remain cold and even build frost under some conditions. At this point, if an acceleration is attempted, the vacuum will drop, fuel will no longer vaporize, and will in fact condense on the cold manifold walls until they are fully saturated with wet fuel – this takes about three seconds, during which time no fuel is going into the engine (and thus no power or a “sag”). After the walls are fully saturated with fuel the air flow finally picks up this ultra rich mixture and floods some of the cylinders but not all of them because liquid fuel is notoriously bad for equal distribution.
More fuel (bigger jets) will only slightly help this problem and actually worsen the over rich condition and spark plug fouling and fuel economy.
The solution: Moderate, and continuous heat supply to keep the walls of the inlet manifold warm and the fuel in vapor form. Exhaust heat is fast but requires a butterfly valve in one manifold to force the exhaust flow. Water heat is slower but very clean and not corrosive to aluminum manifolds. This method utilizes the water pump to continuously supply warm water to a passage underneath the manifold. (See attached drawing.) It is sometimes necessary to weld a tube to the manifold, but be sure to obtain intimate contact between the coolant and the manifold wall or floor. Simply tack welding a closed wall pipe to the bottom of the manifold will not result in sufficient heat transfer.
October
1
2010
These pictures should help you find your Chevy 235 or 261 casting number and date.
More information can be found at http://www.inliners.org/ under the topic “CASTING #”
If you still can’t find out what engine you have, E-Mail us a picture of the passenger side of the block and we will look it up.
September
17
2010
Tom’s top ten list of things to check when diagnosing your engine
1. Check for vacuum leaks at the gasket between the manifold and head and also around the carb base.
2. Check idle vacuum at manifold– should be 15 – 20 inch Hg. and steady.
3. Check for carb flooding or dripping at idle by looking down the carb throat with a good flashlight. (air cleaners removed).
4. Check ignition initial timing – should be approximately 10o B.T.D.C. with vacuum advance unhooked.
5. Check vacuum advance function – will the diaphragm hold vacuum?
6. If you have a distributor with points, check upper bushing wear by pushing the rotor “north to south” and then “east to west”. If you have an HEI, check rotor-to-cap terminal alignment at cylinder #1 firing.
7. Check individual cylinder power at idle by pulling each spark plug wire and note RPM loss for each cylinder.
8. Check cranking compression (with throttle open).
9. Are all the rocker arms going up and down? Check lash.
10. Check for internal crack or hole in intake manifold heat chamber.
rev. 18-Sept-2010
September
17
2010
On any rebuild of the Chevy 235/261 engine, especially if hydraulic lifters are to be used, it is essential to pay particular attention to several areas of the oil pump (even if it is a NEW pump!). Very few pumps actually need replacement, so a complete disassembly, cleaning and re-assembly will usually suffice, but special attention must be paid to eliminate any air leaks on the inlet side of the pump. (Small leaks on the output side of the pump are not of concern).
Air leaks on the inlet side of the oil pump will allow air to mix with the incoming oil. Experience has shown that this air collects in the lifter galley and may cause hydraulic lifters to become “SPONGY” and result in lifter noise.
Air in the oil is not good for the bearings but it is disastrous in hydraulic lifters. It will cause them to become soft, “spongy” and very noisy especially at highway speeds. (Like brakes, with air in the lines).
Three areas have been identified and are suspect even on new pumps:
1- BOTTOM COVER: Assure flatness, freedom from nicks and burrs, and the oil pump must have a gasket or use loctite #515 or equivalent anaerobic sealer. (Do NOT use RTV!)
Assure .002” – .005” gear axial (end) clearance.
2- PICK UP TUBE: Use loctite sealer on the threaded joint where the tube screws into the pump. Make sure the threads are in good shape and the tube has not been squashed oval in this area. An oval tube may feel tight in the pump, but it will allow air to enter the oil stream.
3- OIL PRESSURE RELIEF PISTON: Too much clearance between the piston and its bore can cause an air leak into the pump because this area is open to air in the crankcase and could allow air into the inlet side of the oil pump. I suggest plugging the end of the bore and drilling a .060” vent across into the inlet hole of the pump. Be careful not to cover the vent hole when installing the plug.
These three areas are often overlooked by many engine rebuilders who are mostly familiar with the Chevy V8 and other modern engines which employ an oil pump which is submerged in oil. All three of the previously mentioned potential inlet side air leaks are inherently not possible on the Chevy V8.
The GMC 228, 248, 270 and 302 engines use a loose fitting pick-up tube into the pump body which, I’m sure leaks air but this engine cannot use hydraulic lifters due to lack of a feed gallery. Racing experience on this engine indicates that the bearings apparently do okay with some leakage so I wouldn’t disassemble your entire engine to revise the pump unless, of course, you’re having bearing problems or the engine is apart for other reasons.
On any rebuild of the Chevy 235/261 engine, especially if hydraulic lifters are to be used, it is essential to pay particular attention to several areas of the oil pump (even if it is a NEW pump!). Very few pumps actually need replacement, so a complete disassembly, cleaning and re-assembly will usually suffice, but special attention must be paid to eliminate any air leaks on the inlet side of the pump. (Small leaks on the output side of the pump are not of concern).
Air leaks on the inlet side of the oil pump will allow air to mix with the incoming oil. Experience has shown that this air collects in the lifter galley.
Air in the oil is not good for the bearings but it is disastrous in hydraulic lifters. It will cause them to become soft, “spongy” and very noisy especially at highway speeds. (Like brakes, with air in the lines).
Three areas have been identified and are suspect even on new pumps:
1-BOTTOM COVER: Assure flatness, freedom from nicks and burrs, and the oil pump must have a gasket or use loctite #515 or equivalent anaerobic sealer. (Do NOT use RTV!)
Assure .002” – .005” gear axial (end) clearance.
2-PICK UP TUBE: Use loctite sealer on the threaded joint where the tube screws into the pump. Make sure the threads are in good shape and the tube has not been squashed oval in this area. An oval tube may feel tight in the pump, but it will allow air to enter the oil stream.
3-OIL PRESSURE RELIEF PISTON: Too much clearance between the piston and its bore can cause an air leak into the pump because this area is open to air in the crankcase and could allow air into the inlet side of the oil pump. I suggest plugging the end of the bore and drilling a .060” vent across into the inlet hole of the pump. Be careful not to cover the vent hole when installing the plug.
These three areas are often overlooked by many engine rebuilders who are mostly familiar with the Chevy V8 and other modern engines which employ an oil pump which is submerged in oil. All three of the previously mentioned potential inlet side air leaks are inherently not possible on the Chevy V8.
The GMC 228, 248, 270 and 302 engines use a loose fitting pick-up tube into the pump body which, I’m sure leaks air but this engine cannot use hydraulic lifters due to lack of a feed gallery. Racing experience on this engine indicates that the bearings apparently do okay with some leakage so I wouldn’t disassemble your entire engine to revise the pump unless, of course, you’re having bearing problems or the engine is apart for other reasons.
Tom Langdon
September
12
2010
Welcome Back! Please enjoy our site. If you cannot find something call us. Be respectful, we will not post spam. We invite any feedback about the new look and the new functions.
January
1
2010
CAST IRON MANIFOLDS FOR ALL CHEVY 194, 230, 250, 292 CAR AND TRUCK APPLICATIONS AND INCLUDING “NO WELD DESIGN” FLANGE AND SEAL KIT $275.00!!!
Provides clearance to all inlet manifolds, motor mounts, and clutch linkage.
April
1
2002
NOISY HYDRAULIC LIFTERS ON CHEVY 235, 261 Rev. 20 Sep 2010 bas
Much has been written and experimented with to resolve this recurring problem. Apparently air is entering the lifter from the inlet side of the oil pump or other source. Different lifters, sealed pumps, sealed pick-up tubes & sealed by pass circuits have had much success but not 100%.
After trying many of the above fixes, Grant Galbraith found 100% success by providing a small vent on each of the offending locations. Locate the noisy position and remove the lifter. Wipe with lacquer thinner and tape off the hole on the side and the entire top. Using a bench grinder, grind a “flat” on the outside of the lifter between the annulus and the top of the lifter. Grind about .005″ to .007″ deep. This will provide a “vent” for any air collecting in the lifter galley so that this air does not enter the lifter and cause it to be “spongy” and noisy.
Oil pressure will only be reduced by approximately 1 PSI at IDLE (If all 12 lifters are modified)
Tom Langdon
