Used flat tappet cam break-in???? - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 07-12-2008, 07:46 AM
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Update.....

First of all I want to thank everyone for their input. Lots of interesting posts.

I went ahead and did the break in.
Partly because I was curious, partly because I was too lazy to pull the cam back out, and partly because the engine was in slight need of a rebuild anyways (so, no big loss). And besides, the engine is only on my engine stand (not in the truck yet).

As far as I can tell the cam survived the break in. Ran it for 20 minutes, valve train sounds good, and all the push rods are still spinning. I'll run it for another hour or so and maybe pull the intake and check each lifter wear pattern.

This is a first for this engine!! As far as I know, a flat tappet cam has never lived in this engine. When I got it from a junk truck, the stock cam had flat lobes. And it ate 2 or 3 cams after a rebuild during break-in's. I could hear lobes go flat during the break-in because the exhaust note would change (crazy!!). That is when I converted to a roller cam. I didn't like the roller because the valve train was loud.

The only thing I could find questionable with the engine was the lifter bore diameter. The bores had around 0.0006" bore to lifter clearance. Stock gm specs are 0.0007 to 0.0017". CompCam says 0.0015 to 0.0020. So I chucked up each lifter in a lathe and sanded the sides down 0.0005" with 320 grit sand paper. Took about 2 or 3 minutes each lifter. I know it sounds crazy but it is just the back up engine. But it seems to be working so far which is a really big improvement. I'm thinking the rollers were loud because the lifters were getting struck in the bores.

I'll keep you guys posted when I check the lifters and actually run it down the road.
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Old 07-18-2008, 07:54 AM
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another update...

I pulled the intake last night to check the wear pattern on the lifters. All the lifters had a circular pattern and were all still convex but I still wasn't happy with what I saw. The lifter faces seems to be overly hazy and the circular pattern wasn't as sharp as I would like to see. I'm not going to run the engine like this.

When I ran the engine without the valve covers, the push rods were all rotating but not as fast as I has seen on other engines. Plus oil getting to the top of the engine seemed very low. However, the valve train sounded great! No noise at all at idle or when it was revved up (I liked that).

I guess I should post some lifter face pictures.

I thinking about re-installing the roller cam but using the lighter springs. The hyd. roller setup had a noisy valve train which I hated. It had 130lbs on the seat (I forgot pressure at 0.500"). My light springs have 90lbs on the seat and 270lbs at 0.500". I wonder if 90/270lbs is enough for a very mild roller (206/212 at 0.050") with a 5000 rpm shift point???
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Old 07-18-2008, 12:19 PM
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It was probably noisy before with the Hyd roller because the previous springs were too LIGHT. 130lbs seat in a BBC HYD roller isn't enough, you need 145-155lbs seat 330-350 open. BBC valve train is heavy and needs more pressure if you want to rev over 4500 rpm.
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Old 07-18-2008, 01:06 PM
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Thanks for the response. Maybe too light of a spring? I don't know for sure. The valve train made a clattering noise right off idle. Not exactly high rpms.

Compcam recommends the 911 or 924 spring for the XR258HR. And both have 112lbs on the seat at 1.900" and 309 or 347 at 1.200". I did run the 911 springs but had it installed at 1.850" which gave it around 130lbs and I'm guessing around 325 at 0.500".

I just went to Crane's website and they recommend more like you are saying 130-165 seat and 325 to 375 over the nose. And a minimum of 280lbs for 4000 rpm which I think answers my 270lb question. But my engine was noisy was well below 4000. Just revving up the engine a little over idle would sound like the engine needed a valve adjustment (ugly sound for a hydro cam)

http://www.cranecams.com/?show=howToSelect
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Old 07-18-2008, 09:02 PM
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Point of highest velocity is when the lifter is starting up the lobe and again on the closing side which is why the seat pressure is such an important issue with a heavy valvetrain. Engine rpm has little to do with the noise you are describing, it is the lack of proper valvetrain control that makes it noisy.
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Old 07-19-2008, 01:53 PM
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But the old pressure that I used in the past was within crane's recommendations.

And I'm sure rpm it has a lot to do with it. Sure the ramp is steep but if the engine is at low rpms then the lift rate is not much due to slower cam rotation. Hence the 280 pound minimum required at 4000 rpm.
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Old 07-19-2008, 05:21 PM
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Most pro engine builders will tell you they have found that Crane's and especially Comp Cams Hydro Roller spring recommended rates are all too low. As far as RPM I think you are confusing engine speed with lobe intensity (which is ground into the cam). This is one reason Solid Rollers need even more seat pressure, not just because they are run to a higher rpm.
Example-- If you were to run a .600" lift solid roller with a 80Lbs seat load 220 lbs open load spring it would still run at low rpm but would be extremely noisy and beat the valvetrain to death because the spring can't stay in control of the valvetrain velocity good enough to keep the lifter "glued" to the cam lobe.
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Old 07-20-2008, 11:14 AM
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Your not considering rpm, which has a linear effect on how fast the valve is lifted. Sure the ramp is steep, however the valve rate lift changes with cam rpm and rpm has more effect on valve lift speed than the lobe design. That is the reason why it is possible (and recommended) to break in a cam with only the outer springs. That is... a big aggressive cam will run fine with low pressure at low rpms.
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Old 07-20-2008, 11:56 AM
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Quote:
Originally Posted by 454C10
Your not considering rpm, which has a linear effect on how fast the valve is lifted. Sure the ramp is steep, however the valve rate lift changes with cam rpm and rpm has more effect on valve lift speed than the lobe design. That is the reason why it is possible (and recommended) to break in a cam with only the outer springs. That is... a big aggressive cam will run fine with low pressure at low rpms.
The last few posts are about ROLLER CAMS. Since post # 17.

Roller cams don't get "break-in" time.
Roller lobe acceleration rates are much different that flat lobes.
The clicking is hyd. roller/valve bounce due to too soft springs, usually. (either on the up side or the set down side.)

I would also suggest that the flat tappet lobe face being hazy looking might be due to insufficient break-in time.
MANY builders are recommending 45-60 minutes of break-in time. (It even appears on the CompCams web site)

Last edited by ScoTFrenzel; 07-20-2008 at 12:05 PM.
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Old 07-20-2008, 12:33 PM
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Yes, roller cam don't need a break in. I was just using the light spring during break-in as just an example.

Yes, the roller ramps are faster but only when at the same rpm. A flat tappet will lift the valves quicker than a roller if the flat tappet is cam is spinning fast enough. That is my point, ramp lift rate changes with rpm. Hence the need for stiffer valve springs at higher rpm.
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