Timing belts

[Peter Berbee]

I clipped out a quote from the Subaru "Technicians Reference Booklet" that
covers engines and the changes over the years. The 2.2's from 97 on are of
the interference type.

Peter



""The 2.2 liter (SOHC) (Phase 1) has been enhanced starting

with 1997 model year. The single overhead camshaft

engines have had internal and external changes that yield

an approximately 10 % increase in power and 3% increase

in fuel economy. Accomplishing this involves many factors,

one of which is engine friction reduction.

Redesigned Piston

The piston, a major source of engine friction has been coated

with a friction reducing agent called Molybendum. This thin

coating not only allows a smoother travel through the

cylinder but also reduces cylinder wall scuffing. This coating

will wear off over time and is not an indication of a problem.

The skirt of the piston has been reshaped and the overall

weight has reduced by approximately 100 grams.

Compression ratio has been increased to 9.7 to 1 by

reshaping the crown of the piston. This eliminates the

clearance that was available between the piston at TDC

and a fully opened valve. Piston pin offset has been

changed to 0.5 mm. Piston to cylinder wall clearance has

been reduced by increasing the piston diameter."

 

[Florian Feuser /FFF/]

Looking at the illustration in the maintainance manual,
I suspect both.

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/

 

[Jim Stewart]

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?

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

 

[Jim]

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

 

[Florian Feuser /FFF/]

The change over was in
1099 or 2000.

^^^^

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

;-)

florian /FFF/

 

[Mickey]

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/

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

Mickey

 

[Florian Feuser /FFF/]

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

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

 

[Edward Hayes]

You are wrong

 

[Edward Hayes]

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

 

[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. yes

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

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

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.

Please correct me if I am wrong.

Florian

Mickey

 

[Henry Paul]

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.

 

[Rat]

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.

 

[Jim Stewart]

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.

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

 

[Wayne Farmer]

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

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.

 

[Henry Paul]

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.