GN1 valve clearance problem w decked block

[galoush]

Hey everyone to make the story short i just found out the hard way that my GN 1 heads , comp 218 roller and recently purchased short block arent jiving togther . The valves hit the piston tops and broke a valve just cranking and nicked them . It didnt fire thankfully . The block was done by RPE in Ct. it was decked i realized after taking it apart again . The piston are speed pros . I am using a Cometic .60 gasket . The motor didnt have a problem on the stand but i guess when the lifters pummped up they hit . I really should have checked further . Anyway i see cometic dosnt make a thicker gasket although a special order can be made i belive . Has anyone ever notched the pistions . Has anyone had this problem . Thanks

 

[pwr.slave6]

Yes, my j.e's have been notched for that reason. I'm also running cometics w/ gn1's I can call my eng. builder for the details
on tues. 7/5 if further info is requested.

 

[galoush]

Thanks for the response

 

[tminer]

What rocker ratio are you using? What is piston to deck clearance? Whats the dish like on those pistons and did it hit the bottom of the dish or catch the edge?

I've got the 218/218 with 1.6 rockers (.528 lift) and my valve/piston interferance checked out OK, but now I'm a little worried.

Thanks,
Tom

 

[MSDGN]

Too late now but you should always check the piston to valve clearance before even turning the motor by hand...I used a set of checking springs that I got them from Crane...I have GN1's...JE's with 214/210 roller...T&D 1.65 rockers...lift is .548...clearance was just within specs...block was decked but minimal to just clean it up...I'm also curious as to what rocker ratio you are using...here's some links to Crane...

...this one has info on how to check piston/valve clearance and what the clearance should be...it's what I used when I built my motor:

http://www.cranecams.com/?show=faq&id=2

...this link is the checking springs that I used...

http://www.cranecams.com/index.php?show=browseParts&lvl=4&prt=45

 

[galoush]

The piston to deck clearance was .39 and the pistons are speed pro dished simlair to stock . The valves hit the edges of the pistons. I dont know how much the block was decked, the rockers are 1.6 scorpions .

 

[tminer]

The piston to deck clearance was .39 and the pistons are speed pro dished simlair to stock . The valves hit the edges of the pistons. I dont know how much the block was decked, the rockers are 1.6 scorpions .

Thanks!
Tom

 

[galoush]

I started questioning if i had the cam in right also .Im sure i did anyway ill check everything the right way and post back the deal

 

[HellOnWheels]

it was decked i realized after taking it apart again.



How did you know the block had been decked? Reason I'm asking, I have a 224/224 roller with Harland Sharp 1:65 roller rockers, a SINGLE steel shim gasket, and I know that the heads were cleaned up. So far so good (maybe 8-9k miles), and I'm not for sure but "think" the deck may have been surfaced a time or two!!

DS showed 64-6500 rpm a couple of times due to a really bad trans flare and everything still okay.

Good luck,
HOW

 

[tminer]

I started questioning if i had the cam in right also .Im sure i did anyway ill check everything the right way and post back the deal

I didn't want to ask that, but did wonder.

Mine is in process of getting decked and pistons shaved, but here are the "before" specs: 218/218 .330 but not the standard ICL. GN1 & 1.6 Scorpions. .020 Wiseco pistons (.250" edge, IIRC) at +.009 (using a 6" rod). .057 gasket.

Using a lifter still full of packing grease and checking springs it clearanced fine, but there was a mark in the clay where the valve passed by the edge. I didn't do the test, but did see the piston w/clay. I checked a stock piston and the edge on it was .400" so maybe that would have been enough to make it catch if SPs are similar.

I'd think that the .051 less piston/head clearance on mine would more than make up for the difference in centerline, but I have not done the math. Maybe it is just the wider piston edge.

We figured that with piston about .010 in the hole and .040 gaskets that there would be plenty of clearance, but I'll be triple checking for sure!

Tom

 

[HighPSI]

The piston to deck clearance was .39

Are you sure?

Did you degree the cam in? My guess is it's installed wrong

 

[750H.P.V6]

I agree with Cal. This is the first thing I thought when I read this thread yesterday.

Neal

Are you sure?

Did you degree the cam in? My guess is it's installed wrong

 

[tminer]

Cal & Neil,

Are you basing that on .39 or .039? I assumed he slipped a digit based on .60 head gasket spec, so just trying to clarify.

Thanks,
Tom

 

[HighPSI]

With the piston to deck that large (on a decked block?) coupled with the .060 head gasket, I can't see how it can be anything but an incorrectly installed cam. He's got nearly .100 in the squish area!

I'll ask galoush again:

Was the cam degreed in?

 

[galoush]

The cam was degreed on another motor with a totaly stock bottom end and was within the spec of the card , i didnt do it on this one i just put it in . Well the head will be back this week so ill check everything and let everyone know if it was my mistake ill put that up too . Thanks .039 was the number i belive , my buddy said the motor looked decked because there want any roughness on the top ridge where the lifter valley is . The valves hit the edge of the pistons on on side only the intake valves .

 

[John Wilde]

With the piston to deck that large (on a decked block?) coupled with the .060 head gasket, I can't see how it can be anything but an incorrectly installed cam. He's got nearly .100 in the squish area!

I'll ask galoush again:

Was the cam degreed in?

I agree with Neil and Cal, there is something going on here.
I have run a much bigger cam with decked heads and JE Pistions and never had problems.

 

[S10xGN]

When I set up my engine, I put #1 piston on TDC and a dial indicator on the intake valve stem. With a light check spring installed, I could push the intake valve down 0.485" before it touched the piston top (my cam makes 0.520" max). That's a "worst case" scenario, with the cam correctly timed you should never see anywhere's near this! I'm voting for the cam timing issue.

Russ

 

[frankg]

You must degree the cam every time you install it in a motor or if you change any cam valvetrain components. Like a timing chain. Frank

 

[galoush]

Ok i found out the deal ........I put the cam in wrong..... there is another dot on the set and i must have put it on there and screwed up . I checked the motor with the springs and clay and even rigged a solid lifter to double check with the cam in the right spot it all checked out . I hate making stupid mistakes , well at least the screw up only cost 4bills , it could have been alot worse .

 

[John Wilde]

Ok i found out the deal ........I put the cam in wrong..... there is another dot on the set and i must have put it on there and screwed up . I checked the motor with the springs and clay and even rigged a solid lifter to double check with the cam in the right spot it all checked out . I hate making stupid mistakes , well at least the screw up only cost 4bills , it could have been alot worse .

I am glad that you were able to get things sorted out.

Best regards