were there pre-disco era non-interference engines?

[Tmoose]

I'm thinking non-interference engines were developed shortly after timing belts became popular.

Looks to me like if a valve on any of these 40+ year old OHV engines was left open 0.3 inches or more at TDC the piston would get all Rocky Balboa on it.

http://static.howstuffworks.com/gif/chevy-348-cid-v-8-engine.jpg

http://www.allpar.com/photos/dodge/1960/engines/361.jpg

http://www.allpar.com/photos/dodge/1960/engines/361-wedge.jpg

http://www.amcramblermarlin.1colony.com/photo.html

Yet I don't recall folks building passenger V8s having to replace parts for other than wear reasons.

Aside from the occasional plastic overlayed timing sprocket losing teeth outright, it seems like chain wear would make starting and running so poor that the car was either fixed or thrown away before actual chain breakage would cause the engine's interfer-osity to be tested.

Then again, there are likely to be only a few preferred at-rest positions of the camshaft that would occur naturally due to balance of spring pressure stuffing the lifters against the lobe.

 

[dgallup]

I think actual timing chain breakage practically never occurs in those old OHV pushrod engines. Remember, in those days most of the cars rusted out so fast 100,000 miles was considered high mileage.

Of course, all the (even older) flat head designs are non-interference.

 

[BrianPetersen]

Timing chains did in fact break with some regularity on some OHV engines. But back then, even 60,000 miles was high mileage.

 

[MikeHalloran]

I can't speak for the Dodge or the AMC, but I think the 348 Chevy had big valve reliefs cut in the pistons. I have the impression that most archaic 'merican V8s were non-interference engines, because given that the timing chain was going to break someday anyway, what kinda idjit would not put valve reliefs in the pistons?

As I remember (or mis-remember) history, the phrase 'interference engines' didn't even enter our collective vocabulary here in The Colonies until OHC rice rockets began showing up in volume. There may have been Italian interference engines on our shores before then, but the valves burned so quickly that nobody ever ran one with a really old timing chain..





Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Certainly side valve engines are non interference.

Regards
Pat
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[patprimmer]

I have also seen bent valves on a SBC that broke a timing chain shortly after two boofheads where working on the engine with the throttle return spring disconnected and the throttle jammed wide open. Each thought the other would close the throttle as they started it. They looked at each other as it over reved to the point that a push rod bent and jumped out and the lifter popped a cir-clip and a bit went into the timing cover and wedged between the chain and sprocket. Some people could break a crow bar in a sand pit.

On GM inline sixes similar in principle to Chevy side plate engines, I have also seen gear drives fail and bend valves when the gear drive was made of reinforced phenolic compound.

Regards
Pat
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[Wrenchbender]

I'm not really what my handle says I am (that would be my Uncle Arthur who could verify), but as i recall, a failure mode more common than breakage was a 'jumped timing chain' on older OHV engines. Symptoms were sometimes audible, then very hard or impossible starting & rough idle.

 

[izzmus]

The (nylon) gear failure was very common as mentioned.

It would usually last until the engine needed to come apart for other reasons, though. Good old days?

 

[franzh]

When I was wrenching in the late 60's through the mid 70's, stripped nylon tooth aluminum cam sprockets were a regular occurrence on all US domestic V-8 engines, often by 36,000 miles. GM also had problems with camshafts knocking lobes off and exhaust valves receeding plus the front two rod bearings and the front main bearing. valve top end overhauls before 60,000 miles were common too. Even then, I never remember an interference engine on a US OHV pushrod engine.

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[LadaTrouble]

Chain driven OHC engines were certainly interference.I've seen quite a few engines with inlet valves hitting pistons.And heard it too! Once when adjusting the cam chain on a Lada 2104 I thought it was going to destroy itself right there...I had to shut it down,and de adjust the chain so just the chain rattled,and not the valves and pistons.I've seen Lada's bend valves from a worn camchain too,just not that time.Was common for motorcycles too,particularly Honda's - worn chain,and inlet valves hit the piston,usually with a destroyed top end.

 

[TheBlacksmith]

Let's not forget this was also pre-electronic controls also, so generally the engines ran rich at idle (fuel washdown of cylinders), richer when you hit the throttle (accelerator pump), started going lean (hot and prone to detonate), then rich again as the powervalve opened, then back towards lean at WOT. Timing was also an approximation. Now we can sample the exhaust and make minute adjustments several times a second. It's a wonder all the engines didn't need a total rebuild by the time the timing chain broke.

 

[gruntguru]

worn chain,and inlet valves hit the piston,

Surprising it was the inlet valves. Worn timing chain = later valve timing = more clearance for the inlet valve not less. Were the problems associated with loss of chain tension as well? (Allowing oscillation of the camshaft and thus both early and late timing.)

Engineering is the art of creating things you need, from things you can get.

 

[LadaTrouble]

Every ohc engine with a very badly worn cam chain that has had valve interference has had inlet valves hitting the pistons.Something to ponder over.....

 

[RossABQ]

The only cases I remember of old OHV engines getting intimate were when the valves floated.

My recollection is that early American 4-cyl OHC engines were all non-interference; Chrysler 2.2, Ford 2.3, etc. Seems like the first domestic interference engine was the awful engine in Escorts?

 

[Tmoose]

Here in New England there were stories of Ford dealers full of Escorts awaiting repairs following big snowstorms because the snow managed to sneak into the belt mesh and bust the belt.

 

[LadaTrouble]

''Surprising it was the inlet valves. Worn timing chain = later valve timing''

Which way do you turn a camshaft to retard the timing? Which way will a camshaft rotate in relation to the crank with a badly worn chain?

 

[turbomotor]

Tmoose,

Sorry for the non-helpful post:

I think the flat head in the '49 Merc I had during my high school years in the 70s was non-interference.

Dick

 

[izzmus]

"Seems like the first domestic interference engine was the awful engine in Escorts?"

I'm not entirely certain that engine counts as "domestic", does it?

 

[gruntguru]

"1. Which way do you turn a camshaft to retard the timing?
2. Which way will a camshaft rotate in relation to the crank with a badly worn chain?"

1. Backwards
2. Backwards

Engineering is the art of creating things you need, from things you can get.

 

[patprimmer]

I think a cam that has a lot of backlash in the drive moves back and forward as the engine rotates. The less the number of cylinders and the stronger the valve springs, the more pronounced that effect.

Regards
Pat
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