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Location: Brisbane
Registered: May 2002
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Shim over, Bucket over? Difference?
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Sat, 15 February 2003 11:15
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Hey guys whats the difference between shim over bucket and bucket over shim? Anyone got some pics of both setups? What else is there in the valve train (Buckets, shims...vales, cam/s and springs of course)? Also what are the benefits / disadvantages of each setup?
Also how do hydraulic lifters work?
Cheers
Wilbo
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Location: Montrose, VIC
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 11:33

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Shim under/shim over is relevant in a DOHC setup where the camshaft is directly over the top of the valve e.g. 4ag, etc, etc(NOT SR20!). On the top of the valve there is a thing called a bucket (look at it and it's obvious why) that goes betweek the end of the valve stem and the camshaft. The shims are needed to adjust valve clearance (the gap betweek the base of the cam and the bucket). The difference is that with shim over (e.g. 4ag standard), the shims are on the top of the bucket, whereas shim under puts the shims underneath the bucket. In a standard engine you're not going to gain anything by converting to shim under, but when you start increasing the cams/revs dramatically, then there is potential for the shims on top of the buckets to become dislodged at big revs, causing big damage. Shim under is a way of fixing this.
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I supported Toymods
Location: I renounced punctuation
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 11:37

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They are different ways of adjusting the valve clearance.
Shim over - adjusting shim sits in a recess of the bucket. Cam acts directly on the shim. Advantage here is that the cam doesn't have to be taken out to do the valve clearances. This is OK to a point, but with high lift cams there is a tendency for the shims to be 'flicked out' of the bucket recess at high RPM, causing horrendous damage. Most late model DOHC multivalve Toyota engines are of this design.
Shim under - shim sits in a recess in the valve retainer, and this all sits under the bucket. The cam acts directly on the bucket so there is nothing to flick out. One can put the lumpiest cams and rev not having to worry about spitting out a shim. The problem is that you have to take the cam out to adjust the valve clearance. I believe 2TG, 18RG, and Gen3 onwards 3SGE have this set up. Can also get TRD stuff to suit 4AGE/7MGTE.
No shim - the 1SZ-FE has buckets which have a small adjustment 'nipple' cast into their underside. The buckets are available in a range of different adjustments. Again, this means there are no shims to flick out, but also means that you have to buy a new bucket if the adjustment is out.
I will post pics of both set ups for the 2JZGE tomorrow night.
[Updated on: Sat, 15 February 2003 11:39]
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Location: GoldCoast/Brisbane
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 11:53

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OK so what setup does the SR20 have????
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I supported Toymods
Location: I renounced punctuation
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 11:59

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SR20 = POS rocker arms.
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Location: Montrose, VIC
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 12:26

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Not quite - SR20 actually uses refugee slaves to operate the valves based on a beat knocked out by the cams - work the slaves too hard and they start carking it, with interesting results
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Location: GoldCoast/Brisbane
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 12:32

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Oh no!! So ummmmm how hard do you need to work the slaves.. I mean rocker arms for the SR20 valve train to start experiencing problems???
Me getting worried now!!!
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Location: Montrose, VIC
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 12:43

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Simple - give it to me for a week, I'll letcha know just how much overtime the slaves can handle
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I supported Toymods
Location: I renounced punctuation
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 12:43

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Pretty hard. Plenty of serious SR20DEs out there, but the slaves (rocker arms) breaking in 2 is a known weakness.
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Location: GoldCoast/Brisbane
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 13:00

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hehe MrShin.. yeah I know that revving the shiznit out of it for extended periods of time will have dire consequences, but what I was trying to get at is say I was to do mods to an SR20-DET to double the standard output lets say 250KW @ flywheel, does this alone have a detrimental effect on the life or strength of the rocker arms or is failure a direct result of constant operation in the high rev extreams???
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Location: Brisbane
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 14:17

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Ahh ok sweet, I knew most of that but now its cemented in nicely.
Cheers
Wilbo
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I supported Toymods
Location: I renounced punctuation
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 14:35

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SPEEDCORE wrote on Sun, 16 February 2003 00:00 | .......on the life or strength of the rocker arms or is failure a direct result of constant operation in the high rev extreams???
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M series engines also have rocker arms. My friend and I built a 4M/M hybrid which could rev very hard indeed, but being tight stooges, we didn't replace the valve springs. We had a breakage at above 7000 rpm. We think failure was probably due to excessive rpm with standard valve springs with the sequence going something like this: lumpy cam, soft springs with poor control of valve at high rpm, valve hits piston, valve ricochets back into rocker arm, snapping it off.
Happy to hear other people's thoughts on this.
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Location: Lost in the K hole
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 15:05

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dave, would help to know if the arm that broke was ex or in. story above v unlikely if it was an in valve that broke...
ed
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I supported Toymods
Location: I renounced punctuation
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sat, 15 February 2003 15:08

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Exhaust. Cylinder number 4.
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Club Member
Location: sydney
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sun, 16 February 2003 06:04

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Quote: | M series engines also have rocker arms
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excepting 7M (and posibly 5MG?) which is shim over
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Location: Brisbane
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sun, 16 February 2003 06:05

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And also 6MGE and the 3M was twin as well wasn't it!
Cheers
Wilbo
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I supported Toymods
Location: I renounced punctuation
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sun, 16 February 2003 06:15

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3M was shim under. 7M shim over and 5/6MGE have some horrific hydraulic disaster zone that is best avoided.
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Location: Brisbane
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sun, 16 February 2003 06:16

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Whats the deal with the 5MGE and 6MGE setup? I've never heard of anything?
Cheers
Wilbo
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I supported Toymods
Location: I renounced punctuation
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sun, 16 February 2003 06:20

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The cam acts on a hydraulic backlash adjuster.
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Location: Brisbane
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sun, 16 February 2003 06:31

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And I'm guessing that setup and high revs don't mix too well?
Cheers
Wilbo
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I supported Toymods
Location: I renounced punctuation
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sun, 16 February 2003 06:39

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It introduces inertia (or lag), so it's not ideal for higher rpms. That said, people did manage to get 350-400 hp from stroked (3.2 l) 6MGEs, so they must have got some serious rpm out of them..
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Location: Brisbane
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sun, 16 February 2003 07:33

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Ok I went and looked at the online service repair manual for a 5MGE and why would you use the hydraulic setup? The only reason I got is so you never have to adjust clearances...but won't the hydraulic adjusters stuff up after a while anyway?
Seems like buckets and shims is a way better way to go!
Cheers
Wilbo
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I supported Toymods
Location: I renounced punctuation
Registered: May 2002
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Re: Shim over, Bucket over? Difference?
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Sun, 16 February 2003 08:01

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Bingo! You got it in one.
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Location: 1st street on the right
Registered: November 2002
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Re: Shim over, Bucket over? Difference?
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Mon, 17 February 2003 07:01
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Can the 5mge be converted from hydraulic in any way?
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