i am experiencing a compression problem Inmy front bank, I have 100 psi across all cylinders and on the rear 150. Possible sources? Bad gas? Fuel pump and pressure? Cam belt is off a tooth? Or something else?
Has to be...(unless you somehow used a different measurement method on each bank). What's the background? It was running well, but then something happened; or the timing belts were just replaced, and now no bueno; or ?
That maybe is a little more worrisome series of events -- if it was OK and then "shifted" after assembly and some use, it could shift again (whereas, just being mis-assembled is a more stable situation).
Wonder if the OP has adjustable cam cogs and one came loose and slipped? That would fit the currently known details I think.
Problem solved Can belt jumped a couple of teeth causing low compression and a lean situation. Luckily no damage
Yes very lucky indeed, I wonder how many tooth for the belt to jump before the valve to piston interference?
"Car ran great after an engine out." Sounds like the cam belt tensioner for that bank was set incorrectly during the engine out... If you haven't already, I'd check the tension on the other cam belt. Did you replace the belt that had jumped with a new one? I'd do that as well.
Is it a 2V or 4V? Surprised it could jump two teeth (24 cam degrees and 48 crank degrees!) and not hit the valves.
Depends on which cam and which direction it jumped -- there's a lot of margin one way and not so much the other way for each cam. Pays to be lucky
My rear bank: 15psi all cylinders, front bank: most 170. 77 gtb No obvious problem while turning engine. Belt must have jumped... any suggestions how to proceed please?
Sadly, I think you have no choice but to remove the camcover and timing belt cover on that bank to see what's what.
Pretty much the only way a belt in good condition can "jump" a tooth on an OEM engine is due to incorrect assembly/adjustment of the belt tensioner. As Steve said, only way to proceed is to pull the necessary parts to be able to see the cam and crankshaft alignment marks and go from there...
If tension is set using the spring tension (vs a frequency tester) the spring tensioner must be working properly and proper procedure followed. There is a NA importer bulletin on the procedure. The tensioner should be entirely disassebled, cleaned, lubed and tested by rotating the engine and observing the spring bucket moving in and out. New springs from SPUK are cheap and good peace of mind.
One other way a (non-damaged) belt can skip is if the runout of the belt drive sprocket gets excessive (and a 1977 has the earlier inner bearing + outer bearing + seal + sprocket design that F later updated with inner bearing + seal +outer bearing + sprocket design layout).
well, I cant even believe that I am about to write this next sentence and no one will be believe reading this After 14 months of being in the shop, tomorrow(fingers crossed) I will finally get my 308 back from the shop. And Falbo up in Phoenix has had it for this long and has tried to figure out how to make this 308 mechanically perfect. I don't live up in the area for much of the year so I have not put any pressure on him(obviously) and he knows this so he has never made it a priority. He pulled the engine twice, been up and down each piece of the engine. Problem was, the engine is not stock with performance. Different cams, bigger carbs, jetting, etc. cant say what actually caused the problems but my guess is everything . needless to say, if everything goes as planned, i will take it back tomorrow. Andy says its the fastest 308 he has ever driven(outside of a turbo) based on his 35 mile drive yesterday. Says a lot(if you now who Andy is) I feel like a new owner who will be driving a 308 for the first time
