Retard it back two degrees if its that big a deal. Clearance fixed, done.

My LQ4 is flycut for an old school .590 lift 236/242 XE cam. They just don't have a whole ton of clearance with no valve reliefs.

 

Isn't .032" PTVC a big deal? I thought you'd want at least .100"?

I called Comp back and he said the same thing to retard the cam as well but that sucks doing it that way doesn't it?

Anyone know how thick the piston head is on a LQ4 piston since its already dished?

 

.032 is tight, .1 is overkill. .060 is good in my book with a stable valvetrain.

Retarding the cam is the same as having the cam ground will less advance in it - the motor isn't going to know the difference.

I have .080 reliefs in my lq4 pistons and no issues. Cant comment on how thick the piston is though.

 

.080 is normally recommended.

 

Will retard cam 2 degrees tonight and we'll see what happens. Stay tuned!

 

I ran into this just last week and it was my stupid mistake .If you are checking PVC you will have to pre load your lifter with the heavy springs or your pushrods are going to be too long and will open the valve to much if your using 7.4 pushrods Don't know if that's whats happening to you or not but it did it to me LOL

 

Update, we swapped out the stock timing set with my double roller with adj crank sprocket, retarded the cam 2 degrees rechecked PTVC - we've got more on intake and less on exhaust side just like we should when retarding the cam. We've got .058" on the intake and .060" on the exhaust, what do u guys think?

To comment on the last post, I understand the preload in the lifter but how can u check PTVC with the super tough dual springs?

 

You dont. You use a checking spring. If you use a reg spring, you can run into issues. Unless you have a full on solid lifter you are using in replace of the hyd ones to check degree and PTV.

That is still too close IMO. I would aim for above .060 if at all possible. Esp on a used JY engine.

 

bingo. they are dished but offer no extra clearance.

 

you can use lite springs but u must use a adjustable pushrod set at 0 lash on base circle of the cam a stock pushrod will open the valve to much (to long)and you will have ptv issues .IMO hope this helps I have a lq4 with 243s milled .030 with real close to same profile cam set up on 110 got .105 ptv

 

yeah i have been using a light checking spring, I've only got the stock 7.4" length pushrods to use.

You say you have 105 PTV, you say your using 243 heads, aren't they smaller chambers yet but same size valves? (2.00 Int / 1.55 Exh) So how's this possible that I've got so little PTVC? I don't see how there could be that much difference in PTVC from engine to engine

 

I had some 243s with 2.02 1.60 valves in them milled .015. Had a SNS stage 2 cam in it.(227-235 110lsa) All that cleared the lq4 stock pistons just fine.

 

Are you sure that the 7.4 pushrod is the size you need with your setup? If your setup needs a .025 smaller pushrod for example, the the stock 7.4 is gonna hang that valve .025 more than it needs, and theres your clearance. Measure for pushrod length first and foremost. A pushrod length checker is a must IMO.

 

Hm I didn’t know the OP was having this much a PTV issue with an LQ4 and stock 317 heads? I guess every car is different no matter the setup. When I checked my clearance with the cam and valves (had motor on engine stand) I installed the PR, lifters, spring, rockers on 2 cylinders on each side and hand-turned the crank slowly if anything was hitting between the piston and the valve(cant remember if I used the stock LQ4 springs or the lunati dual springs). Hand-cranked the motor over again once I installed all the PR, lifters, rockers and springs and again nothing felt like it stopped/hit against anything.
OP what are all the stock parts and non-stock parts used?

 

Run it.

For comparison's sake a T-Rex cam has .016-.02 clearance and a MS4 has .025-.03 clearance on a stock ls1, and there are tons of those on the road.

 

This is not meant to be offensive, but this is EXACTLY why I like stock engines and nitrous!!

My brain locked up!! I heard the grind to a halt trying to figure all this numbers yapping out!!

Not that I could NOT figure it out, but its definitely confusing to say the least..

 

Read post #18, I explained how to adjust the rocker arm for 0 lash using a stock pushrod & checking springs. Of coarse if you tighten the rocker bolt, you will be opening the valve and have less PTV.

Russ kemp

 

That method is a recipe for disaster. Read post #18 on how to check your PTV.

Russ Kemp

 

thanks for all the help guys!

Rob, I checked the stock pushrod and it was 7.400" how this all starte is I've got a bunch of parts from my original build from my LS1 vette engine, the original plan was to throw a decent cam, springs, and converter in this LQ4 into my 54 Ford and not have to worry about any issues (PTVC) so i'm using my Harland sharp roller rockers from my LS1 1.7 ratio, 7.400" Trick flow pushrods, SLP double roller timing set, "New" BTR dual .660 springs and obviously new cam, and like any good cam install you check PTVC & degree it in.

After many phone calls I've decided to run this bitch on .058" intake and .060" exhaust......TBD if she'll hold up, don't worry I will find out

 

the 243s area lot smaller 61 cc them milled .030 I really don't think you have a problem with PTV I think your push rod is just to long for checking it with lite springs and no preload on the lifter.order or borrow ajustable pushrod and I think you will find this to be your problem. call comp cams tech line they are pretty helpful I think they will agree with me