?? about U20s

Import_sounds-of-mid-GA · Wed Jan 11, 2006 9:57 pm

Are U20s interference motors or non?? My chain is making a little noise...

datsunfreak · Post by **datsunfreak** » Wed Jan 11, 2006 10:49 pm

Very few 8 valve engines are an interference design. Especially ones with vertical valves.

Typically the 16 valve and "hemi" heads are interference.

datsunfreak · Post by **datsunfreak** » Wed Jan 11, 2006 10:51 pm

But if your chain cuts loose, you'll likely have bigger problems than bent valves...

Victor_laury · Post by **Victor_laury** » Wed Jan 11, 2006 11:32 pm

Yes! Nice holes in the pistons, bent valves, a big ole hole in the valve cover, possible bent rods. all in an instant, long before you even determine something has gone wrong - splat!

Yea timming components are expensive - the alternative is far more. Don't skimp - buy the whole package

SLOroadster · Post by **SLOroadster** » Thu Jan 12, 2006 12:45 am

The good news is that a U20 will tell you that its considering blowing up on you. All you have to do is listen. If something sounds different, or not right, do some looking and you will figure it out nine times out of ten.

Will

Post by **reblues** » Thu Jan 12, 2006 2:34 pm

Yes the U20 is an interference engine.

Richard

Post by **ppeters914** » Thu Jan 12, 2006 2:59 pm

Okay, I'll admit ignorance; what the heck is an interference engine?

Import_sounds-of-mid-GA · Thu Jan 12, 2006 3:37 pm

now, if i say something wrong someone please correct it..... its were if your car jumps timing the valves wont hit each other and/or the pistons

Victor_laury · Post by **Victor_laury** » Thu Jan 12, 2006 6:07 pm

In an interferince engine, Like the U-20, the valves open to a level below the top stroke of the engine. When you lose the timing, the cam stops but the crank does not. Two or more valves will be open to a level where the piston will hit them when it rises to TDC, resulting in a bent valve, a holed piston or possible other expensive nastiness

spyder · Post by **spyder** » Fri Jan 13, 2006 3:07 am

Enough theory, actual practice. Early and isolated in roadsterville! Sloppy chain and devil may care treatment. Chain jumps teeth and valves hit the pistons. No more compression, no more go but no big explosion. I think the angle of the valves in relationship to the pistons kept the damage down. Replaced the bent and sloppy stuff and happy roadstering again!

Post by **dbrick** » Fri Jan 13, 2006 11:57 pm

I used to love Volvo diesels, rubber timing belt, straight up valves and overhead cam with no rocker arms. Belt breaks, cam stops piston hits valve, cam shaft snaps and/or goes straight up along with the bearing caps. Connecting rods bend, occasional broken crank or sunroof in the piston. Big money.
I keep the #1 piston from my Fiat X 1/9 as a reminder to maintain things. It has a 1" x 1 1/2" hole in the top from the timing belt jumping and then breaking at 4000 rpm.

datsunfreak · Post by **datsunfreak** » Sat Jan 14, 2006 8:38 pm

The VW FWD 8V engine is similar, but totally non interference. I had a timing belt tensioner explode at 6500rpm on my '86 GTI. Bought a new belt and tensioner and went on my way again...