Well, I made my first big [screw] up on my first engine building experience.

Long story short I never bothered to check my PTV clearance. Reason I didnt was the cam is quite small (240/250 .558/.558). And the bigger reason, I have SRP -16CC dished blower/n2o pistons with gigantic reliefs in them.

Other specs:
Block was decked to .005
Heads milled to ~52CC chambers (dont know exactly how much)
.039 gaskets

Anyway. I got it running, started right up no problem, except the small cranking problem from the rear mounted battery. Drove it for about 150 miles thinking I was having huge detonation problems. PCM was picking up large amounts of spark knock, so I adjusted timing, took out over 15* to try and cure it and still heard it "pinging". Come to find out it wasnt spark knock obviously it was all the intake valves smacking the crap out of the pistons.

So heres my question now. Every single piston now has about a 1/16" larger intake valve relief and where they hit it left some sharp edges, only one of the pistons was totaled caused by the broken Ferrea valve putting a hole in the #5.

Are these pistons reusable at all? They really dont look that bad thnking maybe i get the valve reliefs enlarged to get rid of the edges the valves made.
Or am I better of starting anew?

Now another question. Joe had me advance the cam 2* to bring the power band down a little bit, could this have caused my troubles? I know advancing it reduces intake PTVC, but if I were to put it straight up next time do you think it would cure it, or would I need to retard it 2*? I know ill have to check this myself, but I dont have enough experience to know how much 2* reduces PTVC.

Thanks fellas. Ill post pics of the aftermath. Im quite proud that it ran this long, those damn valves must be strong as ****, also the piston did not warp or anything, still on the rod perfect in the cylinder except for the "small" hole in the top of it.

One more thing....anybody have 1 LT1 head laying around they dont want?

 

Moving the cam 2 degrees won't cure anything. You will have to cut intake reliefs for the right clearance. It may be that you are way advanced as well without knowing it if you degreed the cam in wrong possibly although you probably would have found that out by now. You might also have been floating or having valves stick in the guides depending on clearance so check it all out. Depending on how much you milled you also may have used up more PTVC there as well.

 

Just be glad it wasn't worse...

http://images.cardomain.com/member_i...79_93_full.jpg

http://images.cardomain.com/member_i...79_94_full.jpg

http://images.cardomain.com/member_i...79_92_full.jpg

Block needed at least one sleeve, heads were pretty much boat anchors.

It can always be worse.
Ryan

 

Yes, check that cam timing. Probably not be where you think it is.....

Ryan,
That was painful to look at... kinda like those surgery shows you accidently come across when channel surfing.

-Mindgame

 

Boat anchors? I disagree The block will need some work, but I think it is salvagable

 

Well, I think a bunch of ported LT1s are boat anchors, but hey...what do I know .

MG, no worries! I needed to give myself a good reason to make some changes . 383, Lloyd Elliot heads, solid roller, and some weight reduction. Hoping for 120mph shakedown passes, and a nozzle setup with as much as it takes to hit somewhere in the low 130s .

When my brother and my friend came over and saw the car all jacked up, their first words were "Dang, that's awesome" .

Ryan

 

More than once I have posted here that PTV clearance must be CHECKED. Don't assume anything unless it's a stock rebuild. Now, maybe people will listen. Anyway, from what you have posted it does seem odd that there was a problem. What was the intake center line you installed the cam at and what is the LSA on the cam?

You need new pistons. Sorry.

Rich Krause

 

Agreed. These won't be boat anchors though

That's also what I was thinking when I saw your car Let me know when you get it ready to hit the track.

 

You guys must have missed my post from last year. Same dang cylinder, but it was worse last time, only thing reused on this engine was the intake Busted valve>busted rod>un-identifiably broken piston>4"hole in cylinder wall+

This time around wasnt quite as bad, I think I owe it to the forged pistons. Lloyd thinks his welder friend can fix the head to look like new though so hopefully that works out.

Last year:
Block
Head\

This time:
Bad Piston
Good Piston
Head


Another thing I really screwed up on was not degreeing the cam which was probably the main reason for all this mess, after talking to Lloyd last night he explained there is a very good chance that the cam was ground big time advanced or retarded already, which I was unaware of being possible. So if it was already 4* plus adding another 2* on top didnt help. So once I guess i need to slap the good head on and degree the cam to find out if cam retarding will help me out or if I need the pistons cut.

BTW after seeing pics of the pistons are they salvageable, I mean if I need bigger reliefs cut anyway couldnt I reuse them?

 

Arn't all LT1 cam's ground with 4* advance?

man those pics hurt to look at.

I just decided that I'm not gonna mill my heads... and maybe 0.045 is safer than 0.039....

Need to place an order for a soft "set-up" spring to check PTV clearance.

 

No, some are advanced 3 or 5 or have no advance at all. Even the LT4 Hot Cam is 3 degrees advanced.

Just be sure to mock everything up before final installation and you should be fine.

 

Curious why you say I need new pistons. If I can just get larger reliefs cut in them that would get rid of the imprints from the valves. Or do you say that because what happened weakened them or something?

Pistons are my biggest worry right now, I would really rather not spend another $550 on pistons if I can use them, they all look fine other than the imprint in them, even the one with the hole in it is still perfect round it looks like, still riding on the rod and everything. But, I also dont want to put the future of the running engine (knock on wood) in jeopardy by reusing them. I will have to talk to my machine shop about this, but wanted some opinions on here.

 

I was making a general statement. It may be possible to salvage the pistons you have. If there is only minor "denting" from the PTV contact a good shop may be able to remachine the piston crown and valve reliefs to a funtional state. You will lose some strength in the crown as the maching will make it thinner and possibly create new stress risers. Also, you will screw up your balance for the rotating assy. It might be better just to get a new set of pistons with the proper clearance.

Rich Krause