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Old 04-23-2010, 01:05 PM   #1
soobaviator
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Default Shimless Bucket vs Shim Over Bucket

I'm looking for some facts, theories and informed opinions on the title subject. The basic question is why did Subaru switch to the shimless buckets? I've heard many claims that the shims were being "spit out" under certain circumstances.

I've seen a number of damaged 2.0L USDM heads, bent valves, chambers blasted by debris from cracked up pistons, but what I have not seen is "spit out" shims. It's very hard for me to believe that the shims could be routinely whipped out of their position atop the bucket. Possibly under a severe floating condition. I'm open to convincing by evidence though.

My own theory, based on what I've had my hands on, is that Subaru changed to shimless buckets because they weighed less than the shim over type and thus increased the threshold for valve float with the same spring pressures. They were also cheaper to produce, maybe...

I'm going to post up some pics and data on the component weights later tonight but I just wanted to get started.



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Old 04-23-2010, 02:48 PM   #2
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shims are an extra failure point
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Old 04-23-2010, 03:05 PM   #3
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There are a few cases of shim issues. They are rare, but happen. I believe one was using launch control with shims, another had a shim that cracked, that's what I recall off the top of my head.

I doubt there is any practical difference of shimless vs. shim under anyone not professionally racing.

The initial cost difference is minimal in terms of manufacturing when considering the volumes Subaru produces or orders. However, the replacement part price difference is rather large. Perhaps this is a cynical view, but MFRs make money on parts. $3 shim vs. $30 bucket?

Given the potential advantage of lighter valvetrain, it's kind of a win-win for Subaru.
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Old 04-23-2010, 03:07 PM   #4
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Originally Posted by Uncle Scotty View Post
shims are an extra failure point
OK, I can accept that Scotty, so how and under what conditions will the shims fail?

I would also add that as a price point for the manufacturer, is it not cheaper to produce a single bucket than a shim and a bucket?
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Old 04-23-2010, 03:18 PM   #5
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My reason for investigating this is that I want to put some built shim over heads on engines that I'm planning to build and I would like to know the risks involving shims. Frankly I don't have any fundamental problem with the shims other than that they appear to be heavier than shimless. I don't think this fact will cause disaster for a street driven car with a 7,500 RPM redline, but I'm seeking more informed opinions...
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Old 04-23-2010, 03:45 PM   #6
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As I said, I think I'm a pretty avid reader here since 2001 and I recall two issues with shim-over heads.

Don't use launch control. Don't bounce off the rev limiter and you should be good unless you're the unlucky one.
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Old 04-24-2010, 01:59 AM   #7
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Quote:
Originally Posted by soobaviator View Post
My reason for investigating this is that I want to put some built shim over heads on engines that I'm planning to build and I would like to know the risks involving shims. Frankly I don't have any fundamental problem with the shims other than that they appear to be heavier than shimless. I don't think this fact will cause disaster for a street driven car with a 7,500 RPM redline, but I'm seeking more informed opinions...
the heads dont care what buckets you use....you can easily(but not cheaply) put the shimless buckets in the heads you have
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Old 04-24-2010, 02:27 PM   #8
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last 3 pictures of post #2, weight of 2 types of buckets ( i do not think shimmed is present):
http://forums.nasioc.com/forums/show...ght=buena+girl
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Old 04-24-2010, 02:58 PM   #9
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last 3 pictures of post #2, weight of 2 types of buckets ( i do not think shimmed is present):
http://forums.nasioc.com/forums/show...ght=buena+girl
This is awesome! Gotta love a chick who can build motors!

She IS comparing shimless to shim over buckets and she beat me to to the measurement in grand style. Yes, the weight savings are quite significant. 22 grams per valve is quite a lot.

She even did the Ti retainer comparison which is great. I weighed the BC Titanium retainers versus OEM. Looks like she used the same ones as my measured weights are nearly exactly the same.

I had considered keeping the shim overs for cost reasons $300 in buckets versus $60 in shims but I could not square that away with knowing they were nearly a full ounce heavier. I'll be going with the shimless buckets for sure and hopefully the stock of buckets I have on hand will suffice without having to buy extra.

With the big weight savings I think it's safe to conclude Subaru changed the design to improve performance and reliability.
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