Camshaft Help

[Johnman45]

Yes and i did a compression test before i messed with the timing and and they were all hovering around 80-90 and the rings on 4 are leaking but i still have 75 compression in 4.

[dalebwilson]

John:

I am no expert like some of the veteran members here but your compression numbers seem low to me. The Haynes manual shows standard numbers between 150-204 PSI. Is your engine EFI or carbureted? If EFI, have you checked the VAF that measures your air intake? Your car will not run if the door inside is stuck. Bottom line is an engine needs 3 things to run: Compression, ignition and fuel. If you have all 3 of these components and they are timed correctly (cam and distributer)....the car will run. Personally, I wouldn't run the engine with a sheared camshaft pin. With those compression numbers, I would pull the head, check the valves, replace the cam, soak the piston rings for a week with sea foam, install new head gasket and reassemble. Some here will suggest just replacing the engine with a used one from a junk yard. That is a viable option as well if you have the skills, tools and time to do so.

[tooldude]

If your engine was running well before the camshaft gear shifted and changed the valve timing, that shows it most likely bent one or more valves, and possibly caused other damage. That would explain the low compression numbers and running problems. The festiva engine is an "interference" engine, as are most 4 cylinder engines, which means the pistons hit the valves if the camshaft timing is shifted too much, as when the timing belt breaks, the camshaft gear or timing belt shifts, or the engine is mistimed by too many degrees. This is properly checked by a leakdown test.

[Tommychu]

The festiva engine is an "interference" engine

Nope.

[tooldude]

Non-interference? then I remembered wrong or got wrong information, but at least I won't have to worry about timing belts breaking anymore.

[dalebwilson]

From Wikipedia:

The Mazda B-series engine is a small-sized, iron-block, inline four-cylinder with belt-driven SOHC and DOHC valvetrain ranging in displacement from 1.1L to 1.8L. It was used from front-wheel drive economy applications to the turbocharged full-time 4WD 323 GTX and rear-wheel drive Miata as well as numerous other models. The Mazda B-series is a "non-interference" design, meaning that breakage of its timing belt does not result in damage to valves or pistons, because the opening of the valves, the depth of the combustion chamber and (in some variants) the shaping of the piston crown allow sufficient clearance for the open valves in any possible piston position.

[tooldude]

If this engine was running well before the cam gear shifted, and then began running badly after the gear was repaired, what does that seem to indicate if not a valve problem? If the valve springs are weak the valves could have been opening farther than designed. I'm wondering what that non-interference dimension is, as in: are the valves just barely clearing the pistons? If that's the case, then a head that's been milled, a block that's been milled, an aftermarket head gasket that's thinner than stock, weak valve springs, and that clearance could be lost. Maybe there's more to this than is stated in the first paragraph. In any case, I believe a leakdown test should be done to check valves, rings and head gasket.

[Johnman45]

Ok so i was finally able to do a leak-down test and everything is good there. it is runs fine when it is at an idle but when i apply gas then it bucks and sputters. What would cause this?

[tooldude]

Mine acted a lot like that when the carb vacuum advance diaphragm began leaking throwing the timing off; or maybe it's another vacuum leak somewhere.

[Johnman45]

I am going to put a new oem carb on do u think that will fix it?

[zoe60]

Check that vacuum advance first. A carb is pretty easy to rebuild if you need to. New might be a waste of money. A bad o2 sensor can cause pretty bad problems with a feedback carb too.