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Senior Member
Camshaft drag
Hi all...I'm assembling my hybrid new IAG short block and reconditioned heads. When the heads were on my workbench, I could easily turn the camshafts by hand with the caps torqued to spec. Now that the heads are on the block and torqued to spec, I can no longer turn the cams by hand. I can, however turn them with a wrench applied at the cam flats but there is a good bit of drag on both the intake and exhaust sides. Is there a specification somewhere on how much static drag is acceptable?
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You could turn the cams easily on the bench with the valve springs and valve buckets installed? I've never heard of a drag spec...
"Good Judgement comes from Experience. Experience comes from Bad Judgement"
Owner: Colonel Red Racing
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818R ICSCC SPM
2005 Subaru STI Race Car ICSCC ST and SPM
Palatov DP4 - ICSCC Sports Racer
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Senior Member
Originally Posted by
Blwalker105
Hi all...I'm assembling my hybrid new IAG short block and reconditioned heads. When the heads were on my workbench, I could easily turn the camshafts by hand with the caps torqued to spec. Now that the heads are on the block and torqued to spec, I can no longer turn the cams by hand. I can, however turn them with a wrench applied at the cam flats but there is a good bit of drag on both the intake and exhaust sides. Is there a specification somewhere on how much static drag is acceptable?
First, i have to say I have very little experience rebuilding Subaru motors.
I have changed timing belts 4 or 5 times.
My experience: with the timing belt off and the cam not contacting the buckets or rocker arms. The cam & pulleys turn very easily. I'm talking turning the cam pulley with my pinky easy.
If the cam shaft is binding after bolting the head to the engine, either the head or the block was not flat. I think that's a serious problem. Hope some engine builders weigh in here.
Bob
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Originally Posted by
Bob_n_Cincy
First, i have to say I have very little experience rebuilding Subaru motors.
I have changed timing belts 4 or 5 times.
My experience: with the timing belt off and the cam not contacting the buckets or rocker arms. The cam & pulleys turn very easily. I'm talking turning the cam pulley with my pinky easy.
If the cam shaft is binding after bolting the head to the engine, either the head or the block was not flat. I think that's a serious problem. Hope some engine builders weigh in here.
Bob
Like Bob said, the cams turn easily until the cam contacts the buckets (lifters). As he suggested, take the heads off and check the flatness of the heads and block. The Subaru spec for the block is Warping limit: 0.025 mm (0.00098 in).
Cylinder Head: Warping limit: 0.035 mm (0.0014 in).
You'll need a high quality machinist straight edge and finer than normal feeler gauge to check them.
"Good Judgement comes from Experience. Experience comes from Bad Judgement"
Owner: Colonel Red Racing
eBAy Store:
http://stores.ebay.com/colonelredracing
818R ICSCC SPM
2005 Subaru STI Race Car ICSCC ST and SPM
Palatov DP4 - ICSCC Sports Racer
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Senior Member
Yes, buckets and springs installed, but I’m rotating them only on the 50 or 60 degrees of rotation before any lobes contact the buckets.
I will pull the heads off and take them to be checked. One would hope a new IAG/Subaru Stage 1 short block would be true.
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Are all the cam caps installed correctly in their respective spots? Remember cylinder 1/3 is on passenger side, 2/4 is on driver side. (I learned this the hard way...)
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Senior Member
Thanks, but yeah, they're all in their respectively correct places. I triple-checked everything and had my race-car-fabricator neighbor even check everything again.
I can tighten any two of the three cam caps and things feel pretty good. When I tighten the third (pick any one), the cam gets tight just as the bolts seat even before torquing to specs. Not much changes after that, but it doesn't feel right to either of us.
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Senior Member
OK, Here's the story. I purchased these rebuilt heads from a supposedly reputable character whose handle rhymes with Pixstar. He assured me that although these heads were from a Saabaru, they were the same as my "03 WRX heads. On initial inspection, they looked fine, although the head surface finish wasn't the best. Without checking all of the camshaft specs, I spent the better part of 10 hrs port-matching, TGV-housing-matching, and opening up the combustion chambers to match the new 2.5L bore of my IAG short block. Fool me Once!! At this point I had a local machine shop CNC-deck the heads 0.001".
After all of the above transpired, I went back to basics and broke out the Plastigauge. Turns out, all of these cams were WAYYYYY tight in their journals, like .0005"-.0008" tight. Factory specs were .0017"-.0029" with a service limit of .0039". On a whim, I decided to measure all of the cylinder head specs and broke out the micrometer. Much to my dismay, all of the camshafts were incorrect or horribly worn (although they looked fine) to the tune of -0.038" of lift. WTF!!!
At this point I was horribly dismayed but decided to check out the cams of my 234,000 mile donor car. I wasn't holding my breath, but lo and behold, every cam was well within factory new specs! I decided to try to match my cams to the rebuilt heads and have spent the last 2 weeks making it happen. At first, all of the cam journals were just as tight as before, so I went about changing those measurements. I found a deep well socket that was slightly smaller than the cam journals, then wrapped it with enough 220 grit wet/dry sand paper to be tight in the bore with the cap bolts tightened by hand. I then sprayed the paper with WD-40 and began to open up each cam journal bore by hand. It took a few times to get my technique right, but by the time I was finished (1 day per cam) I had all the bores about mid-range with about .0022"-.0025" of oil clearance, finishing up with 400 wet/dry.
After holding my breath and having the heads bolted to spec, I carefully tightened the cam caps. Voila!! No binding and everything feels perfect. Now, it's just a matter of backing up a month, probably having to order a dozen new cam buckets and moving forward.
Man, this build just keeps getting more exciting (expensive) every day!! Oh well, In for a penny.....!
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Post Thanks / Like - 0 Thanks, 2 Likes
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Senior Member
Wow... Nice save!
I hope you take a little (more) time to send a nastygram.
818S #332, EZ30R H6, California licensed 01/2019
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Wow that's a really interesting solution with the socket. Good stuff.
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Senior Member
Woo Hoo!! Between the 16 buckets from my donor car and the 16 from the rebuilt heads, I was only 1 short. Strangely, Indianapolis is woefully short of Subaru shops and an afternoon on the phone resulted in ZERO shops with any selection of used or new buckets.
Here is one thing I have discovered: If you call a shop who says they can perform serious engine work on Subaru's and they don't have a selection of new/used cam buckets, RUN away fast! They are NOT Subaru specialists. I spoke to two local shops like this and when I asked about the buckets, one shop said "we ditch all the old buckets" and another shop said "we only order the ones we need at the time". Too funny! Both of these shops listed Subarus on their home pages but showed only pictures of Hondas or other Japanese cars. The local Subaru stealealership quoted the price of one at $36, whereas I procured one online discounted at $18.60 and list priced at $26. Guess we have to now pay the stealerships list price plus shipping within their own infrastructure. It never ends.