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Are V8s often "interference" motors ?

Discussion in 'The Hokey Ass Message Board' started by Dan Timberlake, Aug 7, 2012.

  1. Dan Timberlake
    Joined: Apr 28, 2010
    Posts: 1,331

    Dan Timberlake

    Some of the detractors of belt driven cams complain about "interference" engines that suffer damage when a belt breaks. Not all are.

    Seems like many of the popular V8s needed piston machining just to create safe running clearance if a very frisky cam is installed.
    Or, start missing on a few cylinders if my punk cousin downshifted his hot mom's stock V8 Mustang into second at full speed.
    So, if the chain broke or even wore and jumped a link or 3 the wrong way I'm guessing the pistons could whack the valves in more engines than suspected. Surely Ford 302s and inline 6s were among the ones that had plastic sprockets that would fail badly at mileages approaching 100K.
  2. George
    Joined: Jan 1, 2005
    Posts: 7,460


    SBFs will take the valves out if the chain breaks.
  3. Deuces
    Joined: Nov 3, 2009
    Posts: 21,253

    from Michigan

    Both 5.0L Fox ponys I've bought new came with a double roller timing chain set... ;)
  4. pila38
    Joined: Mar 25, 2009
    Posts: 765


    Did you just call your aunt hot?

  5. [​IMG]
  6. Mr48chev
    Joined: Dec 28, 2007
    Posts: 30,021


    A majority of cars came with plastic tooth timing gears from the factory as they were a bit quieter then metal gears and didn't fostered the engine making noise complaints on new cars that a metal gear might.

    And yes there are a number of non ohc cars that will bend a batch of valves if you loose a timing gear.
  7. King Karl
    Joined: Sep 27, 2007
    Posts: 384

    King Karl
    from N.C.

    That's all I got out of that too! LOL
    Something isn't hitting on all 8 but not sure if it's the motor or not!
    I take that back... Lets see a picture of your hot aunt, then we'll decide.
  8. Heo2
    Joined: Aug 9, 2011
    Posts: 661


    We need pics
  9. 49ratfink
    Joined: Feb 8, 2004
    Posts: 18,111

    from California

    I lost a timimg belt on my OT Volvo. called a Volvo repair/parts place and this dingy lady answers the phone. always right, and always argumentative. quite the bitch.

    first I ask for one of the guys, they are all busy, so I ask her if the 1976 2.1 is an interfereance motor or not. she doesn't know what this is, so I tell her some motors valves hit pistons when the belt goes, while others it does not. I would like to know which type this is.

    she tells me I have to bring it in and they will have a look.

    I explain it again what I am talking about and I get the same line. 2-3 times we go through this, I'm also asking to speak to someone else during all this with no response. finally as I was about to tell her she is a stupid so and so I just hung up.

    found out later this motor does not hit the valves when the belt breaks. that lady is crazy, it is not the first time i have had problems with her.
  10. squirrel
    Joined: Sep 23, 2004
    Posts: 49,789


    235 Chevy is an interference motor, if the timing gear breaks the rods hit the cam and the engine locks up
  11. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,197


    My daughter had the timing chain slip on the original plastic tooth sprocket. on her shit box 307 Chevy....bent some push rods and bent a few valves.
  12. Thumper
    Joined: Mar 7, 2005
    Posts: 1,610


    Well then.........whats your granny like....?......Is she spry...? :D
  13. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    from BC

  14. brad chevy
    Joined: Nov 22, 2009
    Posts: 2,627

    brad chevy

    Lets see maybe you should have called him your stupid punk cousin if he can't drive no better than that. Any engine that jumps time can cause damage. The damage is not always the same either. Just because an engine has a 100 thousand miles doesn't mean its going to jump time.What is your point anyway. You throw your rice burner into second at top speed and see what happens to it.
  15. Screw the engine...Let's see your hot aunt!
  16. Translation: "I have no idea" ....

    I found out how to make a 301 Pontiac an interference motor. Throw a rod and bounce the piston off the valves and it comes down and interferes with the crank.

    But some replacement pistons can have different reliefs in them not because the motor is necessarily interference but because the pistons are made to fit multiple years where heads or valve angles were changed at different points in production, so they can sell one piston for all of them instead of two or three different ones.
  17. squirrel
    Joined: Sep 23, 2004
    Posts: 49,789


    The term "interference motor" really only applies to engines that have a rubber band connecting the crankshaft to the camshaft. If it has a chain, it doesn't matter, because they don't generally break after 75,000 miles.
  18. moefuzz
    Joined: Jul 16, 2005
    Posts: 4,950


    Most over head valve engines will bend valves if the timing chain/belt/gears let go.
    Overhead valve engines have been around for 100 years.

  19. woodypecker
    Joined: Jan 23, 2011
    Posts: 300


    Get a flathead it does not have that problem.
  20. I'm not sure I understand the question.

    Attached Files:

  21. RichFox
    Joined: Dec 3, 2006
    Posts: 10,020

    Member Emeritus

    lots of six cylinder motors are also interference. I know my 270 GMC the cam lobes interfered with the rod caps if the cam/crank timing wasn't right. To say nothing of my Aries pistons and the valves.
  22. bgbdlinc
    Joined: Jan 11, 2002
    Posts: 522

    Member OT DD didn't just twist and murder some valves, it threw them through the block...ruined my day...
  23. Rickybop
    Joined: May 23, 2008
    Posts: 7,305

    from Michigan

    Years ago, I had a 1970 Chevy 3/4 ton pickup, 350 4-bolt engine. Heading down the expressway and the timing chain let go. Rat-a-tat-tat. Got it home and took a look. Along with the rest of the damage, the rocker arm studs actually got pushed out a ways.

    And 235 Chevy rods will hit the cam lobes? Didn't know that. Damn...that's tight.

    Now...concerning your auntie. Is this a Massachusetts thing?
  24. kokomochandler
    Joined: Dec 27, 2010
    Posts: 37


    the op mentioned mentioned two motors but didnt say what was in the hot aunts car. he just said v8. no car with a broken chain is going to run with the chain all bound up in the motor. and since a 5.0 only has once chain theres no way of it running period. a 4.6 has 2 chains but they wont run on one bank because of the firing order.

    but you prolly floated the valve going from 5th to 2nd prolly sent the motor to 12k rpms for a sec and them springs aint made to hold up at that speed.
  25. "T'RANTULA"
    Joined: Aug 6, 2011
    Posts: 662

    from Ohio

    On my c20 I had a composite timing chain gear and it broke and I got some bent valves... Threw a new gear in but it dont run well... Its gettin a fresh rebuilt 355 with no junk composite parts!
  26. moefuzz
    Joined: Jul 16, 2005
    Posts: 4,950


    is that a word or pre teen text messaging?
    Inquiring minds need to know

  27. nrgwizard
    Joined: Aug 18, 2006
    Posts: 1,399

    from Minn. uSA

    Personal experience:

    A *stock* Stude v8 is non-interference.

    A *stock* IH SV v8 is non-interference.

    Modified, both these are "all bets off".


  28. FuelRoadster
    Joined: Nov 17, 2005
    Posts: 1,077


    Has anyone ever *really* heard a loud timing chain/sprocket arrangement on a V8? (unless its so fkng loose that its slapping the cover or block).
    I'm guessing the nylon coated cam sprocket deal was a $$ saving experiment that didnt work...(chunks in the pan when they sheared)
  29. paverguy
    Joined: May 6, 2011
    Posts: 14


    Studebaker V8's had a fiber gear drive. At high mileage there
    was an occasional failure. I experienced one while at normal cruising speed.
    The engine just quit running , and the diagnosis was to remove the Dist. cap and see that the rotor didn't turn when the starter was used .
    Went home on the hook , and replaced the timing gear on the cam.
    Engine was Ok., as Studes have fairly vertical valves , and no interference, and in addition ,not a lot of valve lift.
    BTW , that particular V8 probably had an early cam gear failure due to
    the fact that it had been run as a V4 for about 8000 miles before being
    returned to 8 cyl operation. I'm sure that the V4 mode stressed the gear as clearance was taken up and relaxed in that mode .
  30. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    from BC


    I hear its really tough getting new valves for these...

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