My wife and I have our 1958 Apache 3100 with a rebuilt 235 single barrel carburetor. Nothing fancy. Break-in oil has been changed out by the restoration shop after several hundred miles. The restoration shop did not do the engine rebuild, a reputable machine shop did.
Now that we have several more hundred miles on the truck and engine there is a sudden power loss. Any ideas as to what is going on?
Check the ignition timing. If the clamp around the distributor housing gets a little loose, the distributor can turn in the direction of rotation and retard the timing. A late-timed engine won't get out of its own way. A worn rubbing block at the points can also result in late timing and loss of power by letting the point gap close up. If a little dab of grease isn't applied to the distributor cam as the points are installed, the rubbing block can wear out pretty quickly. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
For all you 235 re-builders out there, I thought I would share the solution to the mystery of why my motor had such a reduction in power all of a sudden. Jerry, you had some good possibilities and I passed those along to the shop.
Just got a call from the restoration shop regarding my drastic loss of power. There is a 'special' drilled head bolt that is required in some of the 235 engines that allows oil to travel up to the rocker arm assembly. When my engine was rebuilt, years ago and not started until recently, the machine shop apparently lost that bolt and just 'stuck' one of the same size back in when they reassembled the engine. Yes, my guy today checked all the head bolts to see if it had been installed in the wrong place when reinstalling the head. He said he did not find it and consequently said he had to make this 'special' bolt.
My guy says the engine runs quiet and has way much more power. Can't wait to see how much rubber I can lay down in second gear!
Hmmmmm- - - - - -just misplacing that bolt is not the cause of your power loss- - - - -the consequences of doing that are far more serious. The oil that lubricates the rocker arms passes through a metered hole in the bolt, which means your rocker arms, and the shafts they run on have been running without lubrication the whole time since the rebuild. They have obviously tightened up, and were trying to stall the engine down. Unless the shop has completely dismantled the rocker arm assembly, inspected all the parts, and repaired/replaced anything that's been damaged by running dry, they haven't corrected their mistake completely. DO NOT accept anything less than a full teardown, inspection, and repair of the top end.
Then there's the issue of where all the displaced metal from running the valve train dry went- - - - - - -Good Luck! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I am not so sure about this drilled bolt business. The drilled bolt is one part of a two part assembly. Its actually a drilled bolt and a plug or cap plug that came with fitted block assemblies post 58. So if you had a shot lower end on a 55-58 motor, you could purchase a fitted block that was service replacement for 59 and up, but in order to use the 55-58 head and rocker assembly on that later block, you had to use the drilled bolt and plug. The reason was that in 59 GM changed the oiling system and made it a more pressurized system that permitted more flow. The 59 and up motors metered this flow different then the earlier blocks and the 59 and up rockers had an offset grove in the rocker to further limit oil flow (55-58 had the grove directly intersecting the dribble hole). The plug stopped the stock oil flow to the rockers, and redirected it to the special drilled bolt that metered the oil to the rockers consistent with oil flow and pressure to the 55-58 motors as opposed to the 59 and up motors. Otherwise, without using the bolt and plug, you would flood the valve train with oil, and possibly have the rockers spit oil over the rocker arms and springs instead of dribbling resulting in a lack of lubrication.
Conversely, using the drilled bolt and plug on a 59 and up motor, with 59 and up rockers, you run the risk of not having enough oil flow to the rockers. This is vitally important because new rocker assemblies are miserably difficult to find these days and a proper rebuilding by Rocker Arm Unlimited in California is not exactly on the inexpensive side.
So what year is your block and what year is your head, and what style rockers are you using?
