2000StreetRod
Moderator Emeritus
- Joined
- May 26, 2009
- Messages
- 10,597
- Reaction score
- 334
- City, State
- Greenville, SC
- Year, Model & Trim Level
- 00 Sport FI, 03 Ltd V8
V8 SOHC not as bad
That's correct. The SOHC V6 has the jackshaft where the camshaft is on the OHV V6. See my post Main timing chain - OHV vs SOHC for more information.
I agree that the chains for both banks should be on the front. The 4.6L V8 has the chains on the front.
I've owned five DOHC engined vehicles during my life (4 Jaguars and an Alfa) and all were equipped with fairly reliable double row roller chains for cam timing. None of them required pulling the engine to replace the valve timing components. However, that was many years ago and not representative of Ford's targeted purchaser today. The 4.6L SOHC and DOHC V8 uses similar chain and guide material to that in the SOHC V6 but the wear is not as rapid and replacement does not require engine removal.
. . . Just from looking at the engine I can see why they've set it up the way they have, but I have to guess at how they're actually doing it. My guess is that this jackshaft you fellows have been speaking of is somewhere in the area of where the camshaft would normally be in a pushrod engine, It runs the whole way through the engine to a sprocket to run a single cam, while the other is run from the front.
That's correct. The SOHC V6 has the jackshaft where the camshaft is on the OHV V6. See my post Main timing chain - OHV vs SOHC for more information.
They only did that to save on the cost of having to have two different cylinder heads designed and made, and in the process doubled, tripled? the amount of expertise, time, tools and patience required to do this job. Which usually means their dealer gets paid and they get to sell you overpriced parts to fix a bad design. Those chains should be on the front of the engine like on every other automotive design. Not to mention that the system is needlessly complex, is inefficient, and has more parts to wear out (which will, because they're made to "Ford's specification").
I agree that the chains for both banks should be on the front. The 4.6L V8 has the chains on the front.
As far as your intuition about the chain guides, yeah. There are only a few engines that use guides similar to yours, and they're part of the aluminum block in some of those engines but there's a huge difference. They use roller chains, similar to a bicycle's, roller chains will only take a tiny bit of metal out and then they ride gently on the metal on the bearings in the links, these engines use separate tensioners. Their guides also don't put nearly as much curve into the chain. Before anyone crys 'oh my god metal shavings', how much do you think your hardened steel pump internals care about aluminum powder?
My old MGB had a rubber tensioner that worked in this manner, sacrifice some material initially so the design of the chain works WITH the design of the tensioner. It was 28 years old and didn't need replacing.
In the case of your engine the chain is not long enough to warrant a tensioner or guide on the working side of the chain for any reason, not even slap. If Ford wanted to be paranoid about slap they should have used an idler gear or smooth pulley, not a piece of plastic against steel, those chains don't exactly have the smoothest backsides. . .
I've owned five DOHC engined vehicles during my life (4 Jaguars and an Alfa) and all were equipped with fairly reliable double row roller chains for cam timing. None of them required pulling the engine to replace the valve timing components. However, that was many years ago and not representative of Ford's targeted purchaser today. The 4.6L SOHC and DOHC V8 uses similar chain and guide material to that in the SOHC V6 but the wear is not as rapid and replacement does not require engine removal.