Who Thinks OHCs are a good idea for V engines?

[bunnspecial]

I guess my cars are a bit backwards. I own one 4 cylinder and one V8-my 4 cylinder is OHV and my V8 is DOHC.

I love the simplicity of OHV engines especially when I have to pull the head and it takes me 30 minutes. The timing chain-if you need to change it-isn't a terrible job.

With that said, timing chain failures seem uncommon. I've known of plenty of Ford Modular V8s(both in SOHC and DOHC form) that went to the graveyard with 300K+ on their original chain and ended up there for some other reason. The AJ-V8 in my car is quite different from the Modular, but I know plenty of folks who have 200K+ and timing chains just never come up. I've known of two or three specific cases.

BTW, I looked at and considered a 1954 Riley RME not too long ago with an I-4. Externally, the engine looks like a DOHC(or "Twin-Cam" in BMC parlance). Dig a bit deeper and you find that it actually has two camshafts mounted high in the block and driving the valves via pushrods. It's certainly a bizarre arrangement from my perspective, but it worked well to make a decently performing engine that had the intake and exhaust on opposite sides on a "Hemi" head

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[Falcon_LS]

Originally Posted By: nthach
If you think that's bad, look at the Ford 4.0L SOHC Cologne V6s in the Explorer/Ranger - 3 separate chains, the engine needs to be pulled to access the right hand chain assemblies.


You read my mind. That was the first thing that came to mind when I saw this thread.

That, and the nylon timing chain tensioners on the 4.6L 2V manufactured between 2000 - 2003. What a nightmare that was.

 

[artificialist]

I'm not sure if you want to call a Volkswagen VR6 a V6 engine or not, but having to replace the timing chain rand related equipment is a pain. When buying and selling VWs one enthusiast formus, somebody will ask if the timing stuff was replaced before.

Anyway, there are some different reasons to prefer a chain over a belt. When a chain is failing, it usually makes bad noises before completely failing. A timing belt can be destroyed without warning if a tensioner pulley, idler pulley, or water pump suddenly seizes. Another thing about chains is that if the front seals of the engine develop leaks, you don't have to immediately replace a chain, but you do have to replace a belt.

THere is one timing chain design that annoys me a great deal. If the water pump is driven by the timing chain and the pump needs replacement, prepare for a long and expensive job.

 

[bunnspecial]

Originally Posted By: artificialist
I'm not sure if you want to call a Volkswagen VR6 a V6 engine or not, but having to replace the timing chain rand related equipment is a pain. When buying and selling VWs one enthusiast formus, somebody will ask if the timing stuff was replaced before.

Anyway, there are some different reasons to prefer a chain over a belt. When a chain is failing, it usually makes bad noises before completely failing. A timing belt can be destroyed without warning if a tensioner pulley, idler pulley, or water pump suddenly seizes. Another thing about chains is that if the front seals of the engine develop leaks, you don't have to immediately replace a chain, but you do have to replace a belt.

THere is one timing chain design that annoys me a great deal. If the water pump is driven by the timing chain and the pump needs replacement, prepare for a long and expensive job.


Both of my cars have water pumps driven separately from the timing gearing-by the(single) V-belt that drive the alternator also on the MG, and by the serpentine belt on the Lincoln.

I've never understood why the water pump has ever been attached to the timing gearing(whether belt or chain). Especially on interference engines, the timing train is so critical that I don't want any extra failure points introduced in that, and I can see a seized water pump snapping a timing belt. With the pump driven by a V belt or serpentine belt, even with a complete pump or belt failure you can often at least limp the car off the road to a safe place. I had the Lincoln blow a radiator hose-which is more or less a functional equivalent of losing the water pump-on the interstate and was able to drive it ~3/4 of a mile to a safe place to pull off.

 

[Alex_V]

I understand the merits of OHC engines (whether chain or belt driven) and many chain designs aren't usually higher maintenance than their OHV counterparts, but especially in a transverse application a number of different OHV V-6's (Buick 3800, Dodge 3.3/3.8, etc.) have been efficient and powerful enough that the potential maintenance hurdles really cast shadows over all the OHC'ers.

The Honda J35 is the bane of my existence.

 

[A_Harman]

If you're building race engines, and the object is maximum power per cubic inch, put double overhead cams in them.
If you're building passenger car engines for the mass market and have to meet fuel economy standards at minimum production cost, put one cam in the block and actuate the valves with pushrods.

 

[RooflessVW]

Power and efficiency are achieved in nearly the same way.

There's a reason most cars are 4 or 5 valve and DOHC.

 

[Cujet]

Originally Posted By: andyd
OH boy ! a 3 foot timing chain relying on plastic rub strips and an oil pressure driven tensioner. What could go wrong? Oh, and if you are Ford, drive one bank from the back of the engine ? That flat head air plane motor looks better and better to me. Especially after a look at the front end of a V-6 stuffed into a Jeep.

I despise unnecessary complexity. And I clearly understand the point. However: http://www.millionmilevan.com/ this guy did 1.3 million miles on a Ford OHC engine. I personally knew of many Ford delivery vans that hit 900K miles. So, done properly, and with sufficient viscosity, the chains last.

 

[Cujet]

It's no wonder the following setup is troublesome:

And this 4 valve setup is amazingly reliable:

Having separate intake and exhaust camshafts does allow for very effective cam timing changes and even allows some engines to operate in Atkinson mode.

Here is a video of the D-Motor, flat head aircraft engine.

 

[TiredTrucker]

I have never been all that fond of V engines in general, and even more so now with this thread discussion.

 

[ChristianReske]

One thing that puzzles me:
All the mechanical chain tensioners worked well.
As the Manufacturers started to switch to hydraulic chain tensioners, trouble beginns.

I still wonder why they have done this change.

 

[Silk]

Hydraulic tensioners have been around for a long, long time - the BMC B block had one in the early '50's. From my experience, the chain runs are too long, and they seem to be very dry compared to earlier chain drive systems.

 

[Shannow]

Originally Posted By: Silk
From my experience, the chain runs are too long, and they seem to be very dry compared to earlier chain drive systems.


Often brought to you by the same companies that thought turning a belt drive through 90 degrees on the Corvair was a sensible thing to do...

 

[Silk]

I've done several of those 3.6 Commodore timing chains, they are practically dry inside the timing cover, and seldom get over 200,000km before needing chains. My Mercedes C220 chain is awash with oil and done over 310,000km.

 

[bunnspecial]

Originally Posted By: Silk
Hydraulic tensioners have been around for a long, long time - the BMC B block had one in the early '50's. From my experience, the chain runs are too long, and they seem to be very dry compared to earlier chain drive systems.


Granted the number of B blocks is pretty limited in the US compared to the UK and Down Under, but neither the one in my car nor the one sitting on my garage floor right now have hydraulic tensioners. In fact, there's no chain tensioner at all-it just loops around crankshaft sprocket and camshaft sprocket.

That is unless you're talking about the DOHC(AKA Twin-Cam) version of this engine.

 

[Silk]

The A block just had some squishy rubber on the cam sprocket...I thought the B block had a ratcheting oil fed tensioner. But this is a memory system that has seen too many engines over too many years. I've got some manuals in the shed to check, but it's Good Friday and family are about to hit the area.

 

[HangFire]

Originally Posted By: Ducked
Originally Posted By: ARB1977
Neglect is what kills chain drive engines. Keep that oil changed.


I've had one Ford DOHC Sierra (European) break its plastic chain guide. Doubt oil quality had much to do with that.

Call me old-fashioned but I feel making critical, stressed, inaccessible engine parts out of something that looks similar to bakelite is bad behaviour and should not be encouraged, so I'd try and avoid buying another like it.


You mean like the "phenolic resin composite" gear on the gear-drive "Iron Duke" engine, that left me stranded on a shoulderless highway at 86,000 miles?

I'd rather put up with the noise of two steel gears.

 

[Silk]

Originally Posted By: bunnspecial
Granted the number of B blocks is pretty limited in the US compared to the UK and Down Under, but neither the one in my car nor the one sitting on my garage floor right now have hydraulic tensioners. In fact, there's no chain tensioner at all-it just loops around crankshaft sprocket and camshaft sprocket.


After a bit of research, my memory isn't slipping, the BMC B series engine has a hydraulic cam chain tensioner.

 

[SteveSRT8]

Originally Posted By: Trav
Unlike most enthusiast I have no affection for them at all, when you consider they brag about a 600 HP new GM engine and the OW43 had 700 HP in 1969. that's HellCat teritory. The closest thing GM has come to anything really decent in recent decades is the North Star but they frigged that up releasing it before it was perfected. Check out what Pontiac had on the board, the 389 and 421.


Don't forget those old SAE gross hp numbers must be reduced at least 20-30% to compare to SAE net hp ratings. Not even close to Hellcat territory.

And to Roofless VW: Have you seen the production numbers you speak of? There's millions of LS style V8's sold every year! let's see the production numbers for those 5 valve per cylinder vehicles!

 

[Trav]

The OW43 was dyno HP. The L88 had 435 published HP but dyno at over 524 HP and a 429 twisted hemi with minor mods pulled over 800 HP on the dyno. Some of those old engines were a lot more powerful than published HP numbers and were much easier to tune for more HP.

http://www.hotrod.com/articles/ccrp-0910-chevy-l88-427-engine/

https://ateupwithmotor.com/terms-technology-definitions/gross-versus-net-horsepower/