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Why could there be instant and extended power loss after running perfectly fine in a 1969 VW Beetle?

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2008-03-09 14:14:06
2008-03-09 14:14:06

Sounds like you lost torque on your head bolts. They get loose because you've got three metals in your engine with vastly different thermal characteristics. Eventually, the Bug Gods just shake them loose. This is actually a fairly common problem--and Loctite doesn't fix it. And there are no head gaskets--torque and torque alone keeps the seal in place. Lose the torque, lose the seal, lose power. Unfortunately, to retorque the heads you almost need to drop the engine and pull off all the tin. They tell me you can take the tin off the cylinders without pulling the engine, but I've never been able to do it. Fortunately, these engines come out extremely easily: before you start, make a little engine stand out of three 12-inch-long pieces of 2x6. Stand two of them up on end and nail the third one across the other two. If it looks like a squared-off U when you're done, it's right. Now... drain the oil remove the back piece of tin--the one behind the pulleys. Also unhook the accelerator cable, the wire to the coil and the fuel line. Cap the fuel line by sticking a pencil in it. jack the car up, crawl under and remove the two engine-transmission bolts at the top of the engine (17mm wrench). The one on the left side is attacked from under the car, and it's in a REAL choice location--above the clutch lever. You need a ratchet and all the extensions you own to get this one out. (I have seen people cut holes in the pan under the back seat so they could reach this bolt easier, and just hinge the piece back on. If you pull the engine frequently--and some people do--this isn't a bad idea.) The other one you turn from inside the engine compartment. If you're REALLY lucky, a previous owner welded a bolt to the side of the bolthead; if so, the welded-on bolt hits the starter and won't turn any more, and you can take this one out by yourself. If you're not lucky, you need one person under the car holding the top starter bolt with a wrench and a second person turning the nut inside the engine compartment. And if this is the case, once you get this bolt out, take it to a welding shop and give the guy ten bucks to just grab a random bolt out of the trash and tack-weld it to the head of the big bolt. So long as it sticks out sideways, you're golden. Anyway, getting these two bolts out is the hardest part of the whole job. lower the car back down get a 6-inch square of 3/4" plywood. Put it on the lifting pad of a floor jack and stick it under your engine, right under the oil strainer cover. Pump the jack until it just touches the engine. undo the two bottom engine-trans nuts. These you just lay under the car and screw off with your 17mm wrench. Now that you have the engine completely disconnected, pull it back until it clears the trans shaft and lower it down. Once it's down, remove all the tin and the valve covers. Then look at what you have under the head: there are eight big nuts on each side. These hold your heads on. Remove them all. There are also two nuts that hold the rocker arms on. Remove the rocker arms and pull out the pushrods. Then pull the heads away from the engine just far enough to get the rod tubes to fall out. Replace the seals on the tubes (a common source of leaks) and put the heads back where they were. This is optional, but I believe in doing lots of these little things to an engine so long as it's out anyway. To torque the head bolts is a three-step procedure, once you've loosened them all. Before you start torquing, look at the head. You will note there are two rows of head bolts--the big nuts attached to the big studs that are holding your heads on. They run through the cylinders. Let's number them, starting from left to right of whatever side you're on: 1 2 3 4 5 6 7 8 You're going to torque in a criss-cross fashion: 2-7-6-3-5-4-8-1. Use a GOOD torque wrench, preferably one that hasn't been buried under 80 tons of stuff and thrown against the wall forty or fifty times. Start by torquing all the bolts to 7 lb-ft. Do this on both sides, then go away for about half an hour. Watch an episode of MASH or something. It needs the time to settle--seriously! The resting time is most important here. When you come back, torque them to 13 lb-ft and leave for half an hour. Your third torquing will take the bolts to 25 lb-ft, which is your final torque. Leave them for two hours, then go over them one final time to be sure they maintained torque. If any of them didn't, you have a whole new problem: the threads in the case are bad. This can be fixed with a helicoil, but to do it you've got to remove the cylinders--which means a top-end overhaul. I would just spend the $150 or so and buy new ones if that was the case. Oh, and if you've got to helicoil one hole helicoil all of them on both sides of the engine. Once you've got good torque, put the pushrods back in and the rocker arms back on. Torque on the rocker arm nuts is 25 lb-ft. You only have to do it once. You can now do one of two things: you can just adjust the valves, put the tin back on, put the engine back in and go on with your life, or you can change the spark plugs--number 1 and number 3, which are SO entertaining to change with the engine in, go in like a dream when it's on the ground--put a new clutch in since you've got the engine out anyway, then put the tin back on, the engine back in and go on with your life. Be sure to adjust the clutch whichever way you go. This is a good full day's work, and it's best to have a friend around to help. a polluted gas tank,poor fuel pump,go to a shop that has 'current ramping''capabilities for fuel pumps,if there is no miss in the engine when this occurs,you could probably rule out ignition failure,does car have variable valve timing ?a faulty cam sensor can cause this.brakes dragging,bad transmission?hope it helps .genset@ //Dude! You're thinking of the New Beetle! A Classic Beetle is about as technically sophisticated as a lawn mower. It has no variable valve timing, sensors of ANY kind or electric fuel pump.// it is also possible that after running for a while, the oil pressure goes down (probably a leak somewhere between the cranck and the block) this will cause the car to lose power If you have a dead cylinder, do a compression test. Could be a burned valve. The air cooled engines eat the #3 and #1 cylinder exhaust valves if they are not kept adjusted. Sometimes, one has a floating valve, you need to set the valves at least once a year, this could be it. -=dr=- //You need to set the valves every three months on an aircooled VW.// possibly your carb is sticking,your float maybe causing it to flood,check to see if there is a small leak where the carb mounts the motor

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