Timing belts

How would the intake and exhaust valves be able to collide if they are driven by the same cam? Or were you talking about the 1996 - 98 EJ25 only now?

florian /FFF/

Maybe I'm confused. I thought we were talking about the DOHC engine, which has a different camshaft for the exhaust and intake valves.

Thanks for the clarification.

So, at 120,700 mi and with one timing belt replacement at 63k, i probably should be thinking about doing it again soon on my '97 legacy with a 2.2l engine..

Jim

^^^^

you'd think they've worked out the kinks since those REALLY early 2.5l engines...

;-)

florian /FFF/

Reread my post. I specifically mentioned Double Over Head Cam in the sentence talking about both valves being open at same time.

Mickey

I was referring to the entire discussion leading up to your post.

Even though the valves of both the DOHC and SOHC engines would collide if moved independently they would not collide in the SOHC version since they're driven by the same camshaft.

IIRC, you've also stated that you rotated the camshaft with the piston in TDC position without problem.

If this is so, the SOHC EJ25 - even though an interference design - could - in theory - survive a timing belt failure.

Please correct me if I am wrong.

Florian

You are wrong

If a timing belt brakes ALL cams lose synchronization with the crankshaft and if the engine is turning you break it period.

yes

yes

I guess it all depends upon what Subaru's definition of "interference design" is. I'm not sure if we know or have a common understanding of the term as it applies to these engines. My understanding is piston to valve collision. I've not observed valve action on DOHC engine so I don't know how close intake and exhaust valves come to hitting each other if out of sync. That may or may not be possible. I really don't know how close the valves come to hitting the piston on either engine. It may be quite close, close enough that with some build-up on the parts, they may in fact collide.

When I did the timing belt change, I half way expected to feel the interference when I rotated the cam but didn't. That is why I question the statement that the 2.5 SOHC engines are interference designs. This is not a hot button issue for me and is of no real concern other than general knowledge to have.

Mickey

It can be both piston/valve or valve/valve depending on the design. A valve interference would be a DOHC design where the valves are angled such that if both valves are open they will contact each other.

Valve/piston interference is there is no clearance space for an open valve with the piston at TDC. As far as I know, it is possible for a DOHC engine to have both types of interference.

The EJ22 up to 1996 was a Non-interference engine. Part way thru the

1996 model year they modified the heads and did away with the hydraulic lash adjusters replacing them with solid rocker arms requiring check/adj at 105K.

All 2.5's, ALL DOHC and ALL USA spec engines excluding the EG33 since

1997 ARE interference engines.

As long as everyone else is being pedantic (: There's no rocker arms. Cups and shims.

When you did your timing belt change, the 4 pistons may have been positioned by chance so that none of the pistons were near the top of their stroke. In that case, there may have been plenty of room for the valves to move in and out of the "interference zone" without contacting any of the piston heads.

What part of the 1996 year and on what models? I have the complete 1996 Impreza manual and it says nothing of the 2.2 being an interference design, nor of 2 different makes of the 2.2 engine.