dthquazi

This is my first post. I have just completed my first engine build and install. I have referenced this site throughout the build but just haven't registered until now. I have searched the internet for this problem but have not been able to find the issue.

Problem: I have just started the motor up for the second time. The first time, I had a freeze plug that was shooting out water. While it was running, I noticed it was slightly backfiring from the carb due to timing but I dind't notice any other odd noises. It ran for a total of 5 minutes.

I fixed the hole and rotated the distributor a bit to hopefully eliminate some backfire. I started it again and I am getting a very intermittent knock. I have not heard a failing part (I.E. failing rod, rod bearing or other parts), but i have heard spun bearings. I have been unable to determine where it is coming from. I have yet to get the timing set and the carb tuned. I shut the motor off when I started to hear the noise so hopefully I can limit damage.

Motor:
383 with block from a 98 pickup
Sealed power pistons, eagle rods, scat crank
L31 heads with stock valves
Springs:
http://www.summitracing.com/parts/CRN-10309-1/
Cam:
http://www.summitracing.com/parts/CCA-12-433-8/
Holly 750cfm carb
I reused the hydrolic roller lifters and push rods. All pushrods were in good condition. I dont know how to check lifters....soooo this might be a solution.
I was dumb and have never used expensive spark plugs. I got a deal on them so I decided to try them. I tried to gap two of them before I figured out that you are not supposed to gap them. I just threw them in and they have a slightly smaller gap than the rest.

Since this is an intermittent knock I am holding out hope.

Any suggestions. If I missed anything please let me know. I am a little frazzled right now since I have searched all over the internet and youtube videos of knock and have not found what I am experiencing.

If you can point me in a direction it would be much appreciated. I have always found my answers on or through this site.

I gotta go to work...

Rolling Thunder

Well for starters are they any particular conditions when it knocks like reving or anything like that? Also maby post a sound clip if possible? This is one of those cases where it might be helpful.Have you check the oil for water or anything like that?

dthquazi

I have checked the oil and water. It has the sound during idle. I do not have any recording devices on hand. It almost sounds like an intermittent valve sticking and hitting piston. I have not had time to pull the valve covers and check the push rods adjustments. It appears the noise is comming from the passenger side of the block. I am typing this from my iPhone so bear with me.

Stekman

Did you have the heads machined for more lift? If not, you're slamming the retainers into the guide bosses with that much lift.

dthquazi

I was under the impression when I started the build that it would be fine with the springs for the lift. I have recently been reading around and am second guessing. What is max. lift with the springs I have now on the L31 heads? I keep leaning toward the valve area due to the inconsistency of the noise and area I heard it.

Stekman

It's not the springs that set "max lift." It's the installed height, which is controlled by the length of the valve, retainer, and keepers - which, in your case, I am guessing, are all stock. As is the height of the guide boss. You could put a spring with .700" max lift in there with stock components, at stock installed height, and it would still bind. Until you change the distance between the top of the valve seals/guide boss and the bottom of the retainer, you will have interference issues, no matter what spring you use.

The heads have to come off and get machined.

CBR1000RR

iTrader: (1)

I think those heads are only good to about .480 lift. Any more then that and they require machining.

Stekman

Vortec head are actually even less than that due to their postive seals. It's down around the .450"ish range.

CBR1000RR

iTrader: (1)

http://www.jegs.com/webapp/wcs/store...-1&showValue=1
Looks like .475", and yes these are the same as the L31 heads.

dthquazi

Alrighty. I re-read the article and I completly misunderstood it the first time. I was so excited to get this car going and now I have to wait a bit longer. Is it worth having them machined or should I look for new ones. I have a two bolt main and according to my comp cam "cam quest" I am getting close to my max hp with my current set-up.

Stekman

It would be alright to pull them and have them machined. Damaging the heads isn't likely compared to probability of bending pushrods, damaging camshafts, etc.

Bottom line is heads will have to come off. Also, would be wise, as long as the intake is off, pull the lifters and inspect the rollers carefully. Look for any abnormalities. While the pushrods are out, roll them along a known flat surface (counter top works well). Check to make sure that none are bent. Basically, you're doing a complete valvetrain inspection.

In a nutshell, something was knocking around. You're going to have to find out what it was before the next time it's fired up.

Oh, and by the way, welcome "officially" aboard TGO.

dthquazi

I am going to run this by you guys. I have been reading all over that if I run the comp cams 26918 or 26915 and the Comp 787-16 NON-GEN 3 retainers you can run .550 which should be good for my cam. This can be done without machining due to the height of the springs and retainers. Anybody have experience with this set-up here. Just looking at my options here.