Is the 4.3l Interference fit or a non interference fit engin

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YeTI
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Is the 4.3l Interference fit or a non interference fit engin

Post by YeTI »

Is the 4.3l Interference fit or a non interference fit engine?? I have looked all over the net but am unable to find a striate answer. Anyone know?

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Post by HenryJ »

I am sorry, I have never heard those terms used in this application.
Can you define what "interference fit" refers to?

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Post by Jongo88 »

I think he means if the timing chain brakes will it bend the valves. And it will..
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Post by 04crewvt »

If I am not mistaken he is asking if the engine is an interference design where the pistons and valves occupy the same space at different times.
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Good explanation.

Post by YeTI »

Yes i am asking is the 4.3l an interference design where the pistons and valves occupy the same space at different times.

Good explanation.

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Post by HenryJ »

I had not heard it referred to that way before.
I would say that yes it is an "interference fit". Breaking a timing chain could result in piston and valve "interference" ;)

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Post by 04crewvt »

I thought this was a pretty common term

Interference

Depending on the design of the engine, the piston and valve paths may "interfere" with one another and incorrect timing in their movements may result in the piston and valves colliding. (Such designs are also called "interference head" or "interference engines", and include virtually all diesel engines. Conversely, non-interfering engines, such as the Mazda B engine or the Subaru EJ22 flat-4, are called "free-wheeling" or "non-interference" engines.)

In interference designs, regular service is especially important as incorrect timing may result in the pistons and valves colliding and causing extensive engine damage and therefore costly repairs. The piston will likely bend the valves or if a piece of valve or piston is broken off within the cylinder, the broken piece may cause severe damage within the cylinder, often also affecting the crankshaft. Some manufacturers, such as Nissan, have switched back to timing chains for the majority of their engines because of the breakage problems associated with belts. However, in some newer engines, timing belts are designed to last the effective life of the engine. Other manufacturers, such as Toyota, use a mix: timing chains on their interference engines and timing belts on their non-interference engines.

When a timing belt is replaced, care must be taken to ensure that the valve and piston movements are correctly synchronized. The usual failure mode of a timing belt is stripped teeth (which leaves a smooth section of belt where the drive cog will slip) rather than an outright snapping of the belt, which is very uncommon. Correct belt tension is critical - too loose and the belt will whip, too tight and it will whine and put excess strain on the bearings of the cogs. In either case belt life will be drastically shortened. All engines feature an adjustable tensioning roller to allow correct adjustment of belt tension.

A timing belt is typically rubber with high-tensile fibers (e.g. fiberglass or Twaron / Kevlar) running the length of the belt.[3]

Rubber degrades with higher temperatures and with contact with motor oil. Thus the life expectancy of a timing belt is lowered in hot or leaky engines. Newer or more expensive belts are made of temperature resistant materials such as "highly-saturated nitrile" (HSN). The life of the reinforcing cords is also greatly affected by water and antifreeze. This means that special precautions must be taken for off road applications to allow water to drain away or be sealed from contact with the belt. Older belts have trapezoid shaped teeth. Newer manufacturing techniques allow for curved teeth that are quieter and last longer.

Aftermarket timing belts may be used to alter engine performance. OEM timing belts "will stretch at high rpm, retarding the cam and therefore the ignition."[4] Stronger, aftermarket belts, will not stretch and the timing is preserved.[5] In terms of engine design, "shortening the width of the timing belt reduce[s] weight and friction."[6]

The first known timing belt was used in 1945.[7] The German Goggomobil microcar was the first mass produced vehicle to use a timing belt in 1950. The first American vehicle to use a timing belt was the 1966 Pontiac Tempest. The 1966 Vauxhall Slant Four was the first production overhead cam four-cylinder design to use a timing belt, a configuration that is now used in the vast majority of cars built today.
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Post by F9K9 »

04crewvt wrote:I thought this was a pretty common term...................
It is a new one on me and I am surprised it applies to our engines. The first time I was concerned with the possibility was with a '90 Mitsubishi/Chrysler Laser. Recommended timing belt change was 70K and if, it failed then you had the problem of things occupying the same space. :?:
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Post by Jongo88 »

I had 1 1992 cpi 4.3 blow a chain and it bent the valves. Had to pull the heads to get them fixed.
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Post by green02crew »

Speaking of which, what would the service interval be for our timing chain?
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Post by Jongo88 »

The 1992 Blazer had 256,000 when it let go. The last Blazer I had had 207,000 and it was changed at 175,000 and it was still good. There is a way to check it. Take the dizzy cap off and turn the motor the way it runs with a socket by hand. You don't have to move it much. You can line the timming mark up to the tab ot tdc so you have a mark. Then turn it back and watch the rotor. If the rotor turns back with the motor your good. If you have to turn the motor like an inch then you better change it.
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Post by YeTI »

Ok I got it all strate :) Timing chain is OK ! Dame Camshaft sencer was bad. and a PITA to change.

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