Problem with VQ37HR - Tomei 280 cams, CP Pistons

GodISmE · 03-02-2021, 06:45 AM

Hi, I checked valve lash becasue compression was way too low, especially on cylinder 1. My intake cam lash went down to 0.05-0.15mm, so quite a lot! Exhaust side is fine, around 0.30mm on all of them. This is just after 1000 miles done on tracks (track car only). HR Heads were fully refurbished and lash was set at 0.25mm int., 0.30mm exh. Stock HR were used so I suspect this might be the problem. But I want to understand why - is it just the fact that they are two soft compared to upgraded Tomei springs or is it their compressed height? Or maybe somethings else contributed to it?
Any experienced engine builders here?

Cams are Tomei Procam 280/11.3 and 272/11. CP pistons 95.75, 11.6:1.

1slow370 · 03-10-2021, 11:36 PM

it wouldnt be springs when your clearance tightens up either the valve seats have deformed, the valves have stretched, or the retainers have deformed allowing the valve to move up in the head closer to the cam. gonna have to dissasemble, inspect, and have good long talk with your machinist. if the gaps have opened up its premature wear on the cams, lifters, valve tips, and you can replace the buckets to redo the clearance and replace cams if damaged. if the gap opened up and and the cams/followers are worn it COULD be because your springs are to weak causing float and damage.

Edit: you didnt use titanium intake valves did you? if so get them out of your engine before they snap, most of them are junk or only work with special valve locks designed for the special groove the need to have to keep the tops of them from stress cracking and dropping the valve

GodISmE · 03-17-2021, 02:06 AM

No we used stock valves. If this was the machinist's fault, wouldn't I have an issue with the exhast valve lash as well?

I was thinking stock HR springs could be too weak at high rpms around 7500 with such aggresive cam / ramp like the Tomei 280/11,3. They discontinued them and now only offer 282/11,3.
Perhaps it caused the valves to slam or bounce on the seats, no?

1slow370 · 03-17-2021, 07:59 PM

it could but usually you will break a valve, 1000 track miles is a lot of abuse you are going to have to have the valves and seats inspected, was the contact face of the valve ground down significantly from stock? radius cutting the valves and seats reduces the area the valve has to cool and increases the wear on the seat and and the valve because the contact area is smaller. it's really hard to diagnose unless you had a major problem. also your lash was pretty tight best i can find tomei specs .3mm intake .33mm exhaust. the lift on those cams isn't too crazy and the duration is really stretched out so without knowing the ramp rate on the cam its hard to say. what was the max rpm you were running?

GodISmE · 03-18-2021, 03:49 AM

7700 rpm with a soft cut off (ecu closing throttle).

1slow370 · 03-19-2021, 12:55 PM

That doesn't sound too crazy if the springs were indeed the cause you could always have them checked to see if they haven't deformed or lost some tension.

03-02-2021, 06:45 AM	#1 (permalink)
GodISmE Base Member Join Date: May 2017 Location: Poland Posts: 3 Drives: 350z Rep Power: 8	Problem with VQ37HR - Tomei 280 cams, CP Pistons Hi, I checked valve lash becasue compression was way too low, especially on cylinder 1. My intake cam lash went down to 0.05-0.15mm, so quite a lot! Exhaust side is fine, around 0.30mm on all of them. This is just after 1000 miles done on tracks (track car only). HR Heads were fully refurbished and lash was set at 0.25mm int., 0.30mm exh. Stock HR were used so I suspect this might be the problem. But I want to understand why - is it just the fact that they are two soft compared to upgraded Tomei springs or is it their compressed height? Or maybe somethings else contributed to it? Any experienced engine builders here? Cams are Tomei Procam 280/11.3 and 272/11. CP pistons 95.75, 11.6:1.

03-10-2021, 11:36 PM	#2 (permalink)
1slow370 A True Z Fanatic Join Date: Aug 2009 Location: In the D Posts: 3,732 Drives: v8 74 260z ;) Rep Power: 7251	it wouldnt be springs when your clearance tightens up either the valve seats have deformed, the valves have stretched, or the retainers have deformed allowing the valve to move up in the head closer to the cam. gonna have to dissasemble, inspect, and have good long talk with your machinist. if the gaps have opened up its premature wear on the cams, lifters, valve tips, and you can replace the buckets to redo the clearance and replace cams if damaged. if the gap opened up and and the cams/followers are worn it COULD be because your springs are to weak causing float and damage. Edit: you didnt use titanium intake valves did you? if so get them out of your engine before they snap, most of them are junk or only work with special valve locks designed for the special groove the need to have to keep the tops of them from stress cracking and dropping the valve Rusty likes this. __________________ ANSWER PRICE LIST Answers - - - - - - - - - - - - - - - - $0.75 Answers (requiring thought) - - - - $1.25 Answers (correct) - - - - - - - - - - $12.50 Last edited by 1slow370; 03-10-2021 at 11:41 PM.

03-17-2021, 07:59 PM	#4 (permalink)
1slow370 A True Z Fanatic Join Date: Aug 2009 Location: In the D Posts: 3,732 Drives: v8 74 260z ;) Rep Power: 7251	it could but usually you will break a valve, 1000 track miles is a lot of abuse you are going to have to have the valves and seats inspected, was the contact face of the valve ground down significantly from stock? radius cutting the valves and seats reduces the area the valve has to cool and increases the wear on the seat and and the valve because the contact area is smaller. it's really hard to diagnose unless you had a major problem. also your lash was pretty tight best i can find tomei specs .3mm intake .33mm exhaust. the lift on those cams isn't too crazy and the duration is really stretched out so without knowing the ramp rate on the cam its hard to say. what was the max rpm you were running? JARblue and Rusty like this. __________________ ANSWER PRICE LIST Answers - - - - - - - - - - - - - - - - $0.75 Answers (requiring thought) - - - - $1.25 Answers (correct) - - - - - - - - - - $12.50

03-19-2021, 12:55 PM	#6 (permalink)
1slow370 A True Z Fanatic Join Date: Aug 2009 Location: In the D Posts: 3,732 Drives: v8 74 260z ;) Rep Power: 7251	That doesn't sound too crazy if the springs were indeed the cause you could always have them checked to see if they haven't deformed or lost some tension. __________________ ANSWER PRICE LIST Answers - - - - - - - - - - - - - - - - $0.75 Answers (requiring thought) - - - - $1.25 Answers (correct) - - - - - - - - - - $12.50

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03-17-2021, 02:06 AM	#3 (permalink)
GodISmE Base Member Join Date: May 2017 Location: Poland Posts: 3 Drives: 350z Rep Power: 8	No we used stock valves. If this was the machinist's fault, wouldn't I have an issue with the exhast valve lash as well? I was thinking stock HR springs could be too weak at high rpms around 7500 with such aggresive cam / ramp like the Tomei 280/11,3. They discontinued them and now only offer 282/11,3. Perhaps it caused the valves to slam or bounce on the seats, no?

03-18-2021, 03:49 AM	#5 (permalink)
GodISmE Base Member Join Date: May 2017 Location: Poland Posts: 3 Drives: 350z Rep Power: 8	7700 rpm with a soft cut off (ecu closing throttle).