(re)Building my engine - finally - Pontiac GTO Forum
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post #1 of 95 (permalink) Old 09-30-2017, 01:10 PM Thread Starter
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(re)Building my engine - finally

FINALLY - in the process of rebuilding my engine. This time, I'll be using Crower stainless rockers and Crower mechanical roller lifters (with their High Pressure Pin Oiling Option). I'm also stepping it up a little
This cam delivers 15 degrees more duration and 0.020 more lift than the previous one, and does that with 1.5:1 rockers instead of the previous 1.65's.
I'm also using file fit gapless (top) rings.

The new cam needed new springs with more pressure to control it, and those springs needed a taller installed height so instead of taking them out, I bought a cutter and machined them myself. Fun stuff!! And I can be positive they're right. The intakes on the drivers side head were already just a touch deeper than my objective of 1.910, so I had to cut them to 1.925 and will use 0.015 shims on those to bring them back to spec.

I'm doing more test fitting and measuring today.

Bear
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post #2 of 95 (permalink) Old 09-30-2017, 02:55 PM
 
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Sounds like fun. I have done the "web research" and book reading and it seems the steel roller rockers are the way to go versus the aluminum. More money, but you won't have any problems.

1.5 ratio, in my opinion, can be a better choice with the roller cam. The 1.65's with a flat tappet cam opens the valves quicker and the "under the curve" slight gains tooted by some of the engine builders are fine for a race engine, but the required heavier valve spring pressures and repositioned pushrod cup on the rocker arm put additional side loading on the rocker arm stud and even the valve guide. I don't think you really need the 1.65's in your application because the roller cams typically have a fast ramp to open the valves sooner and keep them open longer. Isn't that really what the 1.65's are doing in a flat tappet cam in theory anyway? So you compensated for the change to the 1.5's with the slightly higher lift and longer duration - am I right?

I can't tell from your pics, but do you have the lifter bore braces? I read they are highly recommended when using the roller cams as they can add higher side loading to the lifter bores and that's when they can break. Just added insurance in my book and something I would install if going with the roller set-up.

Did you ever decide on double roller timing chain or gear drive?
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post #3 of 95 (permalink) Old 09-30-2017, 04:29 PM Thread Starter
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I'm in agreement about the 1.65's, especially since that's what sidelined me last summer - a rocker failure

That cam was 236/242 @ 0.050 and made .600 lift (110 LSA installed at 106) - all with 1.65 rockers. It too was a solid roller. This one is 251/257 @ 0.050 and makes .615 lift with 1.5 rockers, also with a 110 LSA and will likewise be installed at 106. It's from Bullet Cams and I like their approach quite a lot. The opening ramps are more aggressive than what I had, even after taking the difference in rocker ratio into consideration. However it has closing ramps that are much gentler and don't slam the valves shut like the Comp profile tended to.

Yes, I will be installing a bore brace this time. I'm running a double roller timing set this time, just like last time, but I'm changing brands.

Bear

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post #4 of 95 (permalink) Old 09-30-2017, 08:25 PM
 
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Sounds good. You will have it up and running again in no time.
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post #5 of 95 (permalink) Old 10-01-2017, 11:22 AM Thread Starter
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Crank end play...
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post #6 of 95 (permalink) Old 10-02-2017, 08:51 AM Thread Starter
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Degreeing the cam. I'm using a Romac/Rollermaster timing set, double roller, 9-way adjustable. It's also 0.005 shorter to make up for the block having been align honed. The fit is very good - VERY little slack.

In order to get the cam intake centerline installed according to Bullet's specs (106 degrees) I wound up needing to use the timing set's 4-degrees advanced setting which, interestingly enough, also caused the 0.050 intake and exhaust opening/closing events to shift about 2-3 degrees from what's printed on the cam card.

I've also included a photo that shows a tip I learned/copied/stole from Paul Spotts. If you file a slight bevel onto the nose of the crank and cam keys, it makes it a TON easier to install the parts that have to engage with the key. Maybe everyone else already knew this, but it was new to me.

Just for grins, I also measured cam lobe lift for both intake and exhaust lobes at every 10-degrees of crank rotation.

Bear
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Last edited by BearGFR; 10-02-2017 at 11:48 AM.
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post #7 of 95 (permalink) Old 10-02-2017, 06:15 PM
 
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Gonna be a race engine with those specs.
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post #8 of 95 (permalink) Old 10-02-2017, 10:18 PM Thread Starter
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Aw, just a plain old pump gas street engine...

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post #9 of 95 (permalink) Old 10-07-2017, 09:03 AM
 
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Since I do not have the knowledge to talk tech , I would like to note that in the above picture you did a nice job with the oak chair placement. The back drop of the chair and angle of the timing chain really draws attention to the iron that seems to float in space. All those horses waiting to stampede with fury and fire.. and then the chair beckons comfort and a naturalism to your endeavor. Nicely done. Its that attention to detail that is impressive to me. Keep up the good work. Cant wait to see it all done. Seriously , I envy your ability.
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post #10 of 95 (permalink) Old 10-07-2017, 01:57 PM
 
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squirrelbox--humor is always appreciated...
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