[pherron]

I'm a novice trying to learn, so please be gentle. I have a 1997 24-valve 3.2L SOHC Trooper, and I'm curious about the "SOHC" part. Looking at the engine, the "V" part of the V-6 is obvious, and I can clearly see the 2 banks of 3 cylinders each. The timing belt cover is clearly shaped like a "V" also. It just seems to me that there would be a camshaft over the top of each of the two banks of cylinders and that this would be called DOHC. Does DOHC mean two camshafts in each bank, and SOHC mean one camshaft in each bank? Maybe there's a camshaft for the exhaust valves and another for the intake valves for DOHC and just one camshaft for all valves in each bank with SOHC. You can see that I know just enough to be very dangerous. Thanks for your help.

ph

 

[anthonyn]

Yes DOHC has two cams per 'bank', which further implies 4 valves per cylinder.

 

[serranot]

You can also have SOHC running 4 valves through a rocker system. The advantage to DOHC is that you can more positively control the valve train. The more distance between the cam and the valve, the more slop and mass you build into the valvetrain. Engines that rev relatively high need to keep the slop and mass low else things start to float because of inertia.

Regards,
Tom

 

[Kevo]

Think of it this way:

One cam in per head = Single overhead cam

Two cams in per head = Double overhead cam

In DOHC you have one cam that operates the intake valves for that bank of cylinders and one cam for the exhaust.

In SOHC you have one cam operating both sets of valves.

 

[Tad]

With DOHC it is possible to have no rocker arms. The cams can just sit on top of the valve stems. The early 2nd gen (92-97) DOHC has rocker arms though. The 2nd gen (98+) DOHC doesn't. The 2nd gen (98+) also requires valve adjustments because they use shims between the valve stem and the camshaft. The early 2nd gens have hydraulic adjusters in the rocker arms, which eliminates the need to adjust valves.

-Tad

 

[pherron]

Great info. Thanks alot for the replies everyone.

Thanks Kevo, that's an easy way to remember it.

Tad, I have a 97 but it's SOHC. So which category does it fit into? (2nd Gen, etc). You already told me earlier today that I have hydraulic lifters.

Thanks.

 

[Tad]

You have the early 2nd gen There was a split in 1998 (although be careful, Isuzu sometimes assembled some transition year vehicles that had the "wrong" parts for that model year - 1998 in the Trooper/Amigo/Rodeo. In the 1st gen Trooper it was 1987-1988.

-Tad