Main timing chain - OHV vs SOHC

[2000StreetRod]

Even though Explorers from 1991 thru 2001 were powered by the OHV V6 I was not able to find any photos of it's main timing chain on the forum. There were hardly any threads that even discussed it. However, there are numerous threads posted on the forum about the SOHC V6 timing chains. I'm confident that the reason for the lack of OHV threads is because it has proven to be very reliable. I have been unable to find a photo of the timing components mounted on the engine with the timing cover removed. However, the photo below shows an OHV crankshaft sprocket, camshaft sprocket, timing chain, guide, and tensioner.

Please notice that the chain guide has a straight slot for the chain. When the guide is mounted on the block it does not tension the chain. It merely restricts the chain from deviating from a straight line as the crankshaft sprocket pulls the chain to rotate the camshaft sprocket. Also notice the length and thickness of the chain contact surface on the tensioner. While you can't see it in the photo, under the temporary installation keeper is a plunger that pushes the contact surface against the chain.

The photo below shows the crankshaft to jackshaft chain installed on a SOHC V6.

Please notice how the guide deflects the chain inward toward the other half. One problem with this design is the deflection results in significant guide wear. As the guide wears away the distance from the crankshaft sprocket to the jackshaft sprocket decreases resulting in a change in crankshaft to camshaft timing. Also notice the absence of the chain contact surface on the tensioner. It appears to have been completely worn away. The photo below shows a worn and new tensioner.

The method of tensioning and the robustness of the tensioner is obviously inferior to that of the OHV tensioner. Ford's redesign of the SOHC tensioner can be seen in the photo. It appears to be limited to enlarging the mounting base and possibly changing the composition of the contact material. I am concerned about spending the time to tear down my engine to replace the tensioner with such a flimsy component of questionable reliability. My first thought was to try and use the OHV tensioner and guide but there are significant differences in the mounting bolt holes on the two blocks.

Does anyone know of an aftermarket tensioner that is more robust?

 

[my pos mounty]

Sort off way off topic, but related.
This reminds me of the Harley twin-cam design. If you look at all the cam chest upgrades for that engine, they all get rid of the tensioners and replace them with gears. Maybe someone with the skill/know how could adapt a set of gears to take up the slack? Maybe something spring loaded?

Just thought I would throw this thought out there

 

[my pos mounty]

If you use your imagination, and can disregard my really bad "paint" skills...

Imagine a spring loaded gear on a plate, bolts to the two pre-existing bolts to the right of where my really bad blue circle is. Couldn't somebody with a hell of alot more skill than I make something like that? Even if you delete the "spring loaded" part.

 

[2000StreetRod]

wrong side & gears

Switching to gears would require three gears in order to keep the jackshaft rotating in the correct direction.

The tensioner should be on the slack side of the chain and not on the side that the crankshaft sprocket pulls the chain to rotate the jackshaft.

 

[ranger7ltr]

OHV Timing Chain pics...Courtesy of Joe Dirt...

Even though Explorers from 1991 thru 2001 were powered by the OHV V6 I was not able to find any photos of it's main timing chain on the forum. There were hardly any threads that even discussed it. However, there are numerous threads posted on the forum about the SOHC V6 timing chains. I'm confident that the reason for the lack of OHV threads is because it has proven to be very reliable. I have been unable to find a photo of the timing components mounted on the engine with the timing cover removed. However, the photo below shows an OHV crankshaft sprocket, camshaft sprocket, timing chain, guide, and tensioner.


http://www.explorerforum.com/forums/showthread.php?t=262497

post # 5

And on the OHV chain tensioner, the plunger holds tension on the chain primarily by engine oil pressure with a small spring inside the unit...

 

[2000StreetRod]

Hydraulic tensioner

Thanks for the link ranger7ltr. I missed that one. I'm pasting two of the photos into this thread for convenience. Thanks to Joe Dirt for taking the original photos and posting them.

One disadvantage of using springs instead of oil pressure is that springs weaken with age. Some of the DOHC engines I owned many years ago used oil pressure tensioners and a double row instead of single row chain. They were very durable. I suppose the reason Ford switched on their Cologne V6 to springs was to make room for the balance shaft chain, tensioner and guide.

 

[2000StreetRod]

GM V-6 60 degree engine

I was looking thru my book on how to rebuild th GM V-6 60 degree engine and noticed that there is no tensioner against the chain between the crankshaft sprocket and the camshaft sprocket. There is just a double sided guide between the two sprockets that limits the inward deflection of the chain. The sides of the guide are straight and only contact the chain when it deflects inward.

The text mentions that the engine is extremely hard on the timing chain and gears. It also advises changing the gears any time that the chain is changed because the gears and chain wear into a unique, interrelated pattern. If a new chain is installed on used gears the life of both will be shortened.

 

[2000StreetRod]

DOHC 4.6L timing chain

I found a photo on the forum of a 1997 DOHC 4.6L engine.

The guides on the traction side are straight and do not deflect the chain. As the traction side guide wears due to chain flex the timing will not change. The tensioner on the slack side is the ratchet style combination of spring and oil pressure similar to that used on the OHV V6. Apparently chain guide wear and chain failure is also a problem with this engine. However, a design improvement over the SOHC V6 is that the chains for both banks are in the front. The chains, cassettes, tensioners and sprockets can be replaced after removing the front timing cover. Removal of the engine is not required. I would like the next vehicle I purchase to have one of these engines!

 

[Joe Dirt]

Thanks to Joe Dirt for taking the original photos and posting them.

I was just going to search for my pics, and saw those and thought "wow- someone already put some up..."

 

[wow97]

i have one question when i should do i timing chain on my 97 ford explorer 4.0 e.f.i v-6 sohc i have around 146,000miles when i start it you can hear timing chain sound

 

[2000StreetRod]

Noise progression

I first started hearing startup timing chain noise infrequently at 151,000 miles as cold weather began. It increased in magnitude and frequency signficantly in 1,000 miles. Eventually after the noise begins there will be metal to metal contact resulting in metallic particles in the oil. Even if the chains don't slip or fail then I would be concerned about relying on the oil filter to trap the metallic particles. I happen to have a full flow remote oil filter and a bypass remote oil filter (both excellent quality filters) so my filtration is superior to stock. There's also the remote possibility that plastic guide fragments could collect in the oil pickup screen and reduce oil flow. I would not delay timing chain replacement/repair more than a few thousand miles after first hearing the noise unless you plan to replace the engine upon chain failure rather than repair it.

 

[wow97]

that pic look like my 4.0 e.f.i motor

 

[wow97]

isnt both 1997 4.0 motor both sohc vin x and vin e both sohc

 

[2000StreetRod]

VIN X or E?

If the eighth digit in the VIN is an "X" the engine is the OHV V6. It the digit is an "E" the engine is the SOHC V6. The single overhead cam (SOHC) refers to the number of camshafts per cylinder bank. For example, a DOHC inline six cylinder engine has two cams and a SOHC V6 has two cams. The OHV V6 has one camshaft in the block and none in the heads.

 

[wow97]

i have vin x buti have a 5-speed automatic plus carfax said i 4.0 sohc sfi v-6

 

[2000StreetRod]

SOHC or OHV?

Look at the left (driver side) valve cover. If there is an electrical component (camshaft position sensor) just aft of the crankcase oil filler tube then you have an SOHC. If not, then you have an OHV. If you have an SOHC in a VIN X vehicle then it may be that your engine has been swapped.

 

[wow97]

camshaft position sensor is location at bottom

 

[wow97]

do you have any pictures

 

[wow97]

START 1997 both VIN X AND VIN E BOTH SOHC ENGINE VINE X ONE TIMING CHAIN/VIN E THREE TIMING CHAIN IT COULD I HAVE A 4.0OHC VIN X

 

[2000StreetRod]

CMP sensor photo

do you have any pictures

The photo below shows the camshaft position (CMP) sensor just aft of the crankcase oil filler cap.

It's the component attached to the valve cover with the threaded stud and nut showing and underneath the loom. If you have one of these then your engine is the SOHC V6.