Thanks for the reply. This helps since I’ll setting up a .590 now.
Has anyone else run a tighter lash on the MP mechanical grinds?
How tight to set solid lifters
- Thread starter Texas Red
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Has anyone else run a tighter lash on the MP mechanical grinds?
Well I finally checked the hot lash this afternoon and Newbomb Turk is correct - there is slightly more lash hot than cold on my iron block, iron heads engine. I set them .016" cold thinking I'd get to 0.014" hot, but they are at .018.
Now I have to fix them all, I'll set them to .012.
Another question - when I removed the plugs a few look dodgy - especially drivers side, nearest firewall (labelled Drivers Side No. 4) These are new plugs - I changed them a few weeks back when I did the lash the first time. That plug that came out from that same location looked similar then too, with the central electrode looking burned up/lumpy deposits on it.
The plugs I had in it were NGK BP5S and I went one colder to a BP6S.
I've probably driven the car about 8 times on these plugs, with two long 120 mile highway trips on Saturday and today.
Any ideas what's going on there?
Looks oily to me...worn rings? Compression test may help narrow it down.
FYI in future label plugs by cylinder #, helps keep things "straight"
FYI in future label plugs by cylinder #, helps keep things "straight"
Newbomb Turk
Well-Known Member
I’m glad you took the time to do your lash. Now you know the truth.
BTW, Bewy is correct. I think that 6 is pretty cold. The 5’s look a bit cold.
Some of what you are seeing is fuel distribution. Sometimes you can jet a corner of the carb to clean up a cylinder but it’s a bit harder with a dual plane intake. You just need to be careful and sneak up on it while making sure you don’t change the tune up on a hole you don’t want to change.
If you are running into detonation issues with the 5 plug, you can do some things to get that under control.
First is your timing curve. Without knowing the rest of your combo it’s just a guess but I’m betting you have a fairly fast curve.
Every engine I know of wants a curve. Every engine I know of wants less timing at peak torque and more timing at peak power.
If you think about that for a bit (I’m going to assume some things here) and we say your torque peak is 3800 RPM your engine may only want 24-26 degrees of advance. If you have a curve that’s all in by 2500 (or even 3000) that means whatever your total advance is, you now have way too much timing at peak torque. Thats not only a power killer but it can cause detonation.
Getting a proper curve goes a long way to reducing detonation.
Another way to reduce the tendency to detonate is lowering your coolant temperature. If you are running at say 195 degrees and your cooling system is capable of controlling the temperature at 180 that 15 degrees of coolant temperature will reduce the tendency to detonate.
Between a proper curve and possibly lowering your coolant temperature some you can probably clean most of that up if not all of it.
LIKE ^^^^^^^^
I'll just put this here. Note valve lash hot and cold.
Plug too cold and pig rich. That's what's going on for a start.
Keep in mind it takes the right tune to ignite the horse piss we're getting at the proper time.
Newbomb Turk
Well-Known Member
Yeah, Crane cams and Isky. They have no clue.
Newbomb Turk
Well-Known Member
I agree. If that’s what they think, they are wrong. 66 just did the hot/cold lash and they did NOT tighten up with heat. They never do.
So yes, they are DEAD WRONG. Of course, you could do the same, but you only lash your valves every million miles or so and I probably won’t live that long.
There are varibles that can affect lash, hot vs cold. Cast heads vs aluminum heads, cast block vs alum block, aluminum vs steel ball type vs steel roller rockers, stainless valves vs titanium valves, intake valve vs exhaust valve. Etc.
For me, I'm not sure it's worth figuring out exactly how much all the potential combinations affect lash hot vs cold. Just knowing they might is enough.
The lash on your cam card is a recomendation. If you call your cam manufacturer they will give you a safe range for lash settings based on the cams profile. For example you may find that extra little bit of vacuum you need by setting the lash at the loose end of the range. When we sweep the lash at the dyno to find what makes the motor happy we do it with the motor hot. Since the motor is already hot it wouldn't make sense to wait for the motor to cool off just so we can set the lash cold and then warm the motor back up for the next pull.
If the customer wants to set lash cold that's not a problem. He can check the lash with the motor cold when he gets home and set the lash to that measurement for future cold lash checks. And if he wants to or has to set the lash hot, he already has that measurement.
Setting lash to specs and setting lash to what the motor wants or needs might not be the same setting.
For me, I'm not sure it's worth figuring out exactly how much all the potential combinations affect lash hot vs cold. Just knowing they might is enough.
The lash on your cam card is a recomendation. If you call your cam manufacturer they will give you a safe range for lash settings based on the cams profile. For example you may find that extra little bit of vacuum you need by setting the lash at the loose end of the range. When we sweep the lash at the dyno to find what makes the motor happy we do it with the motor hot. Since the motor is already hot it wouldn't make sense to wait for the motor to cool off just so we can set the lash cold and then warm the motor back up for the next pull.
If the customer wants to set lash cold that's not a problem. He can check the lash with the motor cold when he gets home and set the lash to that measurement for future cold lash checks. And if he wants to or has to set the lash hot, he already has that measurement.
Setting lash to specs and setting lash to what the motor wants or needs might not be the same setting.
69_340_GTS
Well-Known Member
Just found out that cold, or hot, my lash does not change one bit. This is an iron block 340, Edelbrock aluminum heads, with aluminum Harland Sharp roller rockers, and Smith Bros. ball/cup pushrods. I set them all at .022" cold, ran it to full operating temperature and the lash is still .022". Lash of .022" is per 20-246-4 Comp Cams tag (270/270, .468/.468). Even checked it again hot & cold after a few hundred miles with the same result. My theory is that every single piece of metal expands at it's own rate. It just adds up to zero on my combination for some reason. I used exact same method to adjust/check them in the correct order using the degreed harmonic balancer and the adjusting order as shown on an old Mopar decal I have.
Two thoughts on why there can be these hot/cold lash variations on all-iron engines:
- use of aftermarket s/s valves. s/s expands at about 1.5 times the rate of 'normal' steel.
- the steel used in the p'rods.....& just the prods themselves. You have 8-10" of steel tube. The alloying element used with the prod steel might have a high-er expansion rate. Not hard to see a 0.002" difference over 10" of length. Other possibility is how 'heat soaked' the prods were when lash was measured. Once again, slight difference here in temp of the prods is going to make a difference over 10".
- use of aftermarket s/s valves. s/s expands at about 1.5 times the rate of 'normal' steel.
- the steel used in the p'rods.....& just the prods themselves. You have 8-10" of steel tube. The alloying element used with the prod steel might have a high-er expansion rate. Not hard to see a 0.002" difference over 10" of length. Other possibility is how 'heat soaked' the prods were when lash was measured. Once again, slight difference here in temp of the prods is going to make a difference over 10".
So what is the change in temperature, in an engine? 100 degrees F to 200 degrees F? What is the change in temperature of a valve? 100 degrees F to 2800 degrees F? There are many variables in valve lash including where on the base circle you are. Yes, the base radius can be off. That is why I don't pick one point to set my lash, and constantly check as I set the other valves. Best is hot and running, or hot and static. You are up to operating temperature and you check the clearance at all the points on the base circle. The best check is to know your engine and have checked it. See thoughtful posts #88, #89, #90.
340six
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I know late to party. Comp and Engle said same to me
340six
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I did it once on my slant when 15 never again.
stroker402
1968 dart GTS convertible
Why is this so crucial these days ? back in the old days the myth was ......set loose for more top end power or tight for more torque or vise versa.
Loose for more torque.
This is just a thought and these are hypothetical questions, what expands more at operating temps, valve stems and pushrods, or cylinder heads and blocks? Which 2 would effect valve lash the most at temp?
Newbomb Turk
Well-Known Member
I’m pretty sure the Machinist handbook has the data to figure growth of different metals by temperature.
You have to consider the mass of the valve and pushrod compared to the mass of the block and heads. More mass equals more growth.
The pushrod and the exhaust valve don’t have the mass of the block or heads.
Valve lash opens up with heat. Simple as that.
Mass has nothing to with how much expansion a material has. Expansion is based on the length of the object, the co-efficient of expansion for that material & the temperature difference.
The C of E for steel is 0.000012 [ for degrees C ].
Take a 9" prod. The change in length going from 68*f to 150*f is 0.005". Because it is the longest part in the valve train, a small temp change variation can result in a couple of thousandths in length; & because it is on the prod side of the engine, any change in lash has to be multiplied by the rocker ratio.
It is easy to see why some combos vary in the difference between hot & cold lash & there is no hard & fast rule.
The C of E for steel is 0.000012 [ for degrees C ].
Take a 9" prod. The change in length going from 68*f to 150*f is 0.005". Because it is the longest part in the valve train, a small temp change variation can result in a couple of thousandths in length; & because it is on the prod side of the engine, any change in lash has to be multiplied by the rocker ratio.
It is easy to see why some combos vary in the difference between hot & cold lash & there is no hard & fast rule.
Newbomb Turk
Well-Known Member
What deck height are we talking about? a 9 inch pushrod won’t grow more than a 9 plus inch deck height block.
Mass matters because it affects where the casting grows and how much.
No, for the second time, mass does NOT matter. Take a piece of flat steel strip, 1" wide, 1/8" thick & 9" long.
Heat it up so that the temp difference between hot & cold is 100*. Measure the 9" length before & after heating to see how much it has expanded with the heat.
Now take a piece of steel 1" wide, 1/4" thick & 9"long. Repeat the heating experiment. The 9" length has expanded the same amount, but the piece of steel is twice as heavy......
Heat it up so that the temp difference between hot & cold is 100*. Measure the 9" length before & after heating to see how much it has expanded with the heat.
Now take a piece of steel 1" wide, 1/4" thick & 9"long. Repeat the heating experiment. The 9" length has expanded the same amount, but the piece of steel is twice as heavy......
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