 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / Ford / Ford Cars / March 2008250 engine runs terribly
I had my head professionally machined at the auto machine shop. The valves and springs were removed, inspected, and cleaned. The seats were reground. The head looked brand new. I installed the head, new gasket, and rocker arm assembly. This is the first time I ever removed the rocker assembly and cylinder head. I've replaced the exhaust manifold once before and removed every other component several times (carburetor, smog pump, alternator, radiator, all vacuum hoses, etc). I labeled every head bolt, every rocker arm bolt, all the pushrods, and put them back exactly in their original positions. I torqued the bolts in the correct sequence and to the correct foot- lbs. I also labeled every vacuum hose to make sure I put them back where I removed them from. I installed new spark plugs, new oil, and new water/antifreeze. The engine started after a few crankings but there is smoke coming off the carburetor, manifold, head, and valve cover. The engine sounds different and there is no power. I'm going to run a compression test on the 6 cylinders but could I have overlooked anything? I didn't move the distributor and can try adjusting the timing. I rechecked the torque on the exhaust manifold bolts and the rocker arm bolts and half of the head bolts and they were all tightend to specs. The valves are not adjustable as far as I can tell. I've rebuilt VW engines completely with new crankshafts, bearings, camshafts, shells, pistons, rings, and heads with no problems. > I had my head professionally machined at the auto machine shop. The valves > and springs were removed, inspected, and cleaned. The seats were reground. [quoted text clipped - 17 lines] > new crankshafts, bearings, camshafts, shells, pistons, rings, and heads with > no problems. I wonder if the timing is off a few degrees (like a tooth on timing gear). Jeff >I had my head professionally machined at the auto machine shop. The valves and springs were removed, inspected, and cleaned. The >seats were reground. The head looked brand new. I installed the head, new gasket, and rocker arm assembly. This is the first time [quoted text clipped - 8 lines] >tightend to specs. The valves are not adjustable as far as I can tell. I've rebuilt VW engines completely with new crankshafts, >bearings, camshafts, shells, pistons, rings, and heads with no problems. You stated that the valve seats were re-ground. Did the machinist even bother to lap the valves to allow them to mate better with the "new" sealing surfaces ? Usually when the seats are ground, the valve faces should get a touch up as well as long as there is a sufficient margin then lapped to improve sealing. I know you marked the locations that the head bolts came from but I'm not a real fan of re-using head bolts. Bill >I had my head professionally machined at the auto machine shop. The valves >and springs were removed, inspected, and cleaned. The seats were reground. [quoted text clipped - 17 lines] >completely with new crankshafts, bearings, camshafts, shells, pistons, >rings, and heads with no problems. "azazel scratch" wrote (250 Engine) I had my head professionally machined. Valves and springs were removed, inspected, and cleaned. The seats were reground. I reinstalled the head, new gasket, and rocker arm assembly. I replaced the head bolts, rocker arm bolts and pushrods in their original positions and torqued them in the correct sequence to the correct torque. I installed new spark plugs, oil, and coolant. The engine started after a few crankings but there is smoke coming off the carburetor, manifold, head, and valve cover. The engine sounds different and there is no power. I didn't move the distributor but I can try adjusting the timing. The valves are not adjustable as far as I can tell. I've rebuilt VW engines completely with no problems. I'm going to run a compression test on the 6 cylinders. I have overlooked anything? _____________________________________________________ Smoke coming off the head and from nearby components (valve cover, carb, and manifold is may be surface oil burning off from an overheated engine. Extremely retarded ignition timing, a too-rich fuel mixture, or burned/unseated valves will cause this. The compression test will show if the valves are the problem. When valve seats (and valves?) are reground there is a possibility that the increased valve stem projection will prevent valves from fully closing. The valve lash must be adjusted to compensate: 1.) Mechanical adjusters: Reset valve lash to specs. 2.) Hydraulic lifters w/Sphere nut: Back off nut and readjust. 3.) Hydraulic lifters No-adjust: Install perforated shims under rocker shaft posts. Good luck. Rodan. > "azazel scratch" wrote (250 Engine) > [quoted text clipped - 36 lines] > > Rodan. Ask here. http://fordsix.com/forum/viewtopic.php?t=49720 im wondering what year and vehikle you have.if its the 250 inline 6 with the intake manifold made onto the head, its critical for the valves to stick out of the head at specified hieght or the valves wont close. grinding seats and valves causes the valves to stick out further. lucas http://www.minibite.com/america/malone.htm -------------------------------------------------------------- Beer is proof that God loves us and wants us to be happy. --Benjamin Franklin >I had my head professionally machined at the auto machine shop. The valves >and springs were removed, inspected, and cleaned. The seats were reground. [quoted text clipped - 17 lines] >new crankshafts, bearings, camshafts, shells, pistons, rings, and heads with >no problems. What you describe sounds like tight valves. That is common where the head has been surfaced and/or the valves resurfaced. Machining the head moves the head closer to the cam and resurfacing the valve moves them further up in the heads. Both take up adjustment in the valve train effectively making the valves too tight such that they cannot close fully. There are several ways to get around this and restore proper valve adjustment depending on thr valve train. One way is the use of shorter push rods which is the case on several Ford V8's. If the rockers are the pedestal style used on many Fords, shims are available to place under the pedestal. The ideal way is to grind the end ot the valve while the machinist is doing the valve job to get the exact installed stem height which is specified in the FSM. If the valve stems are too long, there may be no way to restore adjustment short of pulling the head and machining the valves for the correct stem height. All that said, a compression test may not tell you which cylinders are having a problem. You may be able to go one valve at a time turning the engine to get the cam on the base circle and collapse the lifter fully. You can sometimes collapse the lifter by leaving it on the nose of the cam for a few minutes. Keep in mind the lifters also have an internal spring to keep them expanded for quick takeeup on engine start. You will have to overcome this spring pressure when checking clearance. If these are pedestal style rockers, you can loosen them enough to get a feeler guage a bit larger than the max spec in and retorque it. Wait a few minutes to check the clearance. The valve spring will do the work of c=ollapsing the lifter for you. Most Fords I have dealt with need 0.050-0.60" to be sure the lifter is correctly centered when running. The lifters have 0.125"-0.150" or so total travel, IIRC. Keep in mind that a hydraulic lifter is really just an automatic lash or clearance adjuster. With the engine running, the engine oil pressure enters the lifter while it is on the base circle of the cam to expand it taking up any clearance. That position is maintained by a check valve inside the lifter. To ensure the lifter does not overdo it's job, it is designed with a controlled bleed or leak. If the lifter has not clearance when fully collapsed, it may not allow the valve to close. This is not an uncommon problem where a machinist may have cut the valves and seats a little too far in an effort to save the cost and trouble of installing a new valve or seat. In any case, he should have checked each and every valve stem height to make sure it is within specs. I can't recall a competent machine shop that would not have access to these specs. This will also affect valve spring pressures which are correct with shims under the valves. If the machinist did this along with too much stem, you may also get coil bind on the springs which is undesireable and can cause more problems with cam and valve train wear or damage. Lastly, I would advise that you check each and every valve for clearance before you remove anything else. If you do not have clearance, make sure you check each pushrod for bending. A compression check would also be a good idea just in case there is a major *U somewhere > On Thu, 27 Mar 2008 07:55:02 -0800, "azazel scratch" > [quoted text clipped - 81 lines] > > - Show quoted text - if i was him i would not run the the motor to much with those valves to tight it will wipe the cam and lifters
|
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.