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Car Forum / Driving, Maintenance, Tuning / General Car Topics / May 2007Interference Engine List
The timing belt tensioner bearing failed after a dust storm while on the free way. The belt burned up and the cam shaft valving didn't work. I got all kinds of contradictory answers on the kinematics of the engine, not only from mechanics and parts stores, but in the literature. Is there any reliable guide to engines where the pistons occupy the same space as the valves [at different times]? I seem to have zero compression after installing the new belt and tensioner. Even igniting starting fluid is impossible. Bret Cahill >Is there any reliable guide to engines where the pistons occupy the >same space as the valves [at different times]? > >I seem to have zero compression after installing the new belt and >tensioner. Try: http://www.gates.com/chooseCountry/index.cfm?CFID=7524569&CFTOKEN=81457788 Pick your country and scroll down to : Auto Aftermarket - Timing belts Scroll down some more and find interference engines - fill in the blanks. and get all the Gates data for your application (belts, hoses, caps, ) Pete Do bent valve stems mess up the holes in an aluminum head? Does this require a lot of machine shop work or can I just replace with new valves? Bret Cahill >Do bent valve stems mess up the holes in an aluminum head? Does this >require a lot of machine shop work or can I just replace with new >valves? Depends. Some engines might break a valve or bend them and you will need some machining or replacement heads or you get lucky and no damage. It all depends on where the valves were at the time of breakage. Ive had it both ways and wound up replacing a head from a broken valve that pierced a water jacket. I've had bent valves that just required replacement and lapping in - no machining. Who can say what actually happened to yours without doing some testing or teardown. If your sure you got the engine timed in correctly, pull the spark plugs out, squirt about an ounce of oil (5/6 squirts) in each hole and do a compression check. When you spin a engine over trying to start, the fuel still goes into engine and gives you gasoline wash and lose of compression and high wear from dry rings and pistons. Do this first before taking the engine apart. Then do a pressure test - air pressure in each hole (needs a threaded hose in the park plug hole and a compressor) and listen for leaks in the intake and exhaust. You have to roll the engine over to a compression stroke while doing this for each hole. This might be hindsight to tell you that timing belt change schedules are cheaper that engine work. And when buying a used car, check and replace the timing belt immediately, if there is no tag saying when it was replaced. Pete > Do bent valve stems mess up the holes in an aluminum head? Does this > require a lot of machine shop work or can I just replace with new > valves? You might be able to just replace the valves. But, the pistion hits the valves. This can destroy a piston. I have seen a piston with a valve stuck in it (with the stem in the top of the piston). And the cylinder head itself can be destroyed. You need to get the engine apart to see how much damage there is. Better yet, change the belt when you're supposed to. Jeff > Bret Cahill > You need to get the engine apart to see how much damage there is. That just made things more confusing. I'm not a forensic scientist but I couldn't see any damage. I couldn't even see where the valves knocked any crud off the pistons or vice versa. Turning the cam shaft, all the valves _looked_ like they were seating properly. The pistons have indentations machined into their tops to accomodate the valves when they are open. Open at the right time or any time, I do not know. But the depth of these wells plus the head gasket thickness is just about the same distance as the maximum extension -- at least _after_ the timing failure -- of the open valves past the head seating surface. So maybe it is a non interference engine. Or maybe it was a non interference engine before 1/16" of crud formed on the pistons. I measured the clearances as closely as I could, to ~ 1/32", and figured it wouldn't make much sense to design an interference engine with a pressure ratio of 8:1 when you could have a non interference engine with a pressure ratio of 7.95:1 Finally I checked the valve "lash", the distance between the valve stem and the rocker arm when the valve is closed, and all measured 0.027". All this indicates a non interference engine. Yet I suddenly have zero compression. Before I removed the timing belt I checked the timing marks on both the crank shaft and the cam shaft and they were both on top dead center at the same time. > Better yet, change the belt when you're supposed to. Actually it was the tensioner pully bearing that probably failed first. Had the belt failed first the tensioner would still be rolling. Nevertheless I either knew or, as the lawyers say, "should have known" that all the dust storms we've been having out here in the SW desert destroy machinery. I'm almost afraid to look at my air filter. Yesterday a local Auto Zone store had an ad on the door: "Replace your tensioner and extend your timing belt life." I thought, "yea, NOW they tell me. I bet they don't run these ads in the Pacific Northwest." Bret Cahill Bret, it really sounds like your valve timing is 180deg off. You say the timing marks are both at TDC, did you check a manual to see if you had them lined up right? If both marks were at the top of their pulley's and the marks are supposed to be next to each other that would do it. Jeff DeWitt >>You need to get the engine apart to see how much damage there is. > [quoted text clipped - 50 lines] > > Bret Cahill > Bret, it really sounds like your valve timing is 180deg off. Maybe it's off 120 degrees. The cam sproket was designed for several different engines and has three different marks 120 degrees apart and can fit on the shaft 3 different ways. On several previous t-belt or seal or head gasket replacement jobs I never thought about the sproket being on the cam shaft properly but just used the kinematics to determine timing. The sproket was probably on wrong and since I never took it off this time around, I assumed it was on correct and didn't bother checking the position of the valves as before. Bret Cahill |
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