DodgeTalk Forum banner

Status
Not open for further replies.
1 - 20 of 31 Posts

·
Registered
Joined
·
2,196 Posts
Discussion Starter #1
I have been getting allot of questions on pushrods lately and with the spotty valve train noise issues that show up on virtually the same combination's but are present on one and not on the other I thought I'd share some info on one of the possible causes of valve train noise. Pushrods too short.

5.7 cam base circle diameter 1.615-1.620"

6.1 and all smaller aftermarket cams base circle diameter 1.540"

Theoretical max base circle diameter in relation to lobe lift = 2X lobe lift - #4 bearing dia (2.245")

What this means is:

If you have a 600" lift cam using a 1.65 rocker ratio you would have a lobe lift of 0.364" the largest your base circle can be is 2.245 - 2 X 0.364 which equals 1.517" and since the cam cores come in pre roughed in usually the base circle is smaller yet.

So whats this mean? Well if you have a 600 lift cam in your stroker you need to know what your base circle is so you can order the right length pushrods appropriately.

If you are running a smaller cam like a comp 260-268, crazy jay, Spartan,,,, it's still a good idea to measure base circle diameter because they can be and often are on the small size but the reason some are ticking and some are not is because the 5.7 intake push rod length is 6.610" and the 6.1 intake is 6.650 so the 6.1 intake is 0.040" longer and that's good because the 6.1 base circle diameter is 0.080-0.085 smaller so when you divide by 2 to convert to radius you get 0.0425" and the 0.040" longer 6.1 turns out to be about perfect as long as the base circle of your cam is 1.540"

On the exhaust side the 5.7 push rod is 7.840" and the 6.1 is 7.865" so there is only 0.025" difference and there is then 0.015" of potential problem so if the base circle is slightly small then the problem is yet exacerbated.

Fortunately, there are push rods available in 7.875" lengths which hits it just about perfect. So the best aftermarket cam conversion push rod setup would be a 6.1 intake push rod and an aftermarket 7.875" exhaust push rod. Although, currently most people are using a 6.1's in both locations.

Now if the heads are milled 0.030 the 5.7 intake push rod would only be 0.010" too small which is probably good enough but there is a 6.625" aftermarket available which will only be 0.005" too long so it would be best and then on the exhaust side the 6.1 push rod would be 0.005" longer than target so essentially perfect.

So on a 0.020" milled head use a 5.7 intake would be 0.020" too small (too much) so the 6.625 is definitely the ticket and 6.1 exhaust would be good and the aftermarket 6.625 intake with a 6.1 exhaust would be perfect.

on a 0.020" milled head the 6.625 intake @ 0.005 too small with the 6.1 exhaust would be good and the 6.625 intake 0.010" too bigh with a 6.1 exhaust or 7.875 exhaust would be a good selection too and possibly better because if the base circle is off it's almost certainly too small and the extra 0.005" would benefit.

Now I still definitely recommend measuring base circles particularly if the lift is over about 0.550" but also to a lesser extent if the cam specs are 218 duration or over and if the LSA is tighter or the cam is advanced or retarded. The more the cam varies from the core the smaller the base circle will have to be.

Keep in mind this does nothing for the venerable "Hemi Tic" which is something entirely different but it will fix the problem if it is due to push rods being short from either small base circles or tolerance stack up or a combination
 

·
I RECOMMEND FUKKEN WAX
Joined
·
13,990 Posts
man, that was like reading a rocket science manual!
 

·
Registered
Joined
·
2,196 Posts
Discussion Starter #3
and if your rocket is going tic,tic, tic worth every minute:)
 

·
12.02 na - 11.46 nos
Joined
·
839 Posts
man, that was like reading a rocket science manual!
Stu does know a rocket science ,went to collage with him
could not pass that one up Stu ,lol:D
 

·
Fastest stockblock 4x4 NA
Joined
·
2,695 Posts
where did you guys go to collage? :D :D

And i thought my schoolin sucked!!! :D :D
 

·
Registered
Joined
·
2,196 Posts
Discussion Starter #7
Stu does know a rocket science ,went to collage with him
could not pass that one up Stu ,lol:D
Lol, that's my buddy Dan who's with Lockeed Martin out in ProudHemi's neck of the woods. At the Colorado School of Mines he'd always study twice as much and get a grade lower on the tests. Always pissed him off. Visited last year when I was in GA for the southeast shindig for the LX's
 

·
Registered
Joined
·
762 Posts
I have been getting allot of questions on pushrods lately and with the spotty valve train noise issues that show up on virtually the same combination's but are present on one and not on the other I thought I'd share some info on one of the possible causes of valve train noise. Pushrods too short.

5.7 cam base circle diameter 1.615-1.620"

6.1 and all smaller aftermarket cams base circle diameter 1.540"

Theoretical max base circle diameter in relation to lobe lift = 2X lobe lift - #4 bearing dia (2.245")

What this means is:

If you have a 600" lift cam using a 1.65 rocker ratio you would have a lobe lift of 0.364" the largest your base circle can be is 2.245 - 2 X 0.364 which equals 1.517" and since the cam cores come in pre roughed in usually the base circle is smaller yet.

So whats this mean? Well if you have a 600 lift cam in your stroker you need to know what your base circle is so you can order the right length pushrods appropriately.

If you are running a smaller cam like a comp 260-268, crazy jay, Spartan,,,, it's still a good idea to measure base circle diameter because they can be and often are on the small size but the reason some are ticking and some are not is because the 5.7 intake push rod length is 6.610" and the 6.1 intake is 6.650 so the 6.1 intake is 0.040" longer and that's good because the 6.1 base circle diameter is 0.080-0.085 smaller so when you divide by 2 to convert to radius you get 0.0425" and the 0.040" longer 6.1 turns out to be about perfect as long as the base circle of your cam is 1.540"

On the exhaust side the 5.7 push rod is 7.840" and the 6.1 is 7.865" so there is only 0.025" difference and there is then 0.015" of potential problem so if the base circle is slightly small then the problem is yet exacerbated.

Fortunately, there are push rods available in 7.875" lengths which hits it just about perfect. So the best aftermarket cam conversion push rod setup would be a 6.1 intake push rod and an aftermarket 7.875" exhaust push rod. Although, currently most people are using a 6.1's in both locations.

Now if the heads are milled 0.030 the 5.7 intake push rod would only be 0.010" too small which is probably good enough but there is a 6.625" aftermarket available which will only be 0.005" too long so it would be best and then on the exhaust side the 6.1 push rod would be 0.005" longer than target so essentially perfect.

So on a 0.020" milled head use a 5.7 intake would be 0.020" too small (too much) so the 6.625 is definitely the ticket and 6.1 exhaust would be good and the aftermarket 6.625 intake with a 6.1 exhaust would be perfect.

on a 0.020" milled head the 6.625 intake @ 0.005 too small with the 6.1 exhaust would be good and the 6.625 intake 0.010" too bigh with a 6.1 exhaust or 7.875 exhaust would be a good selection too and possibly better because if the base circle is off it's almost certainly too small and the extra 0.005" would benefit.

Now I still definitely recommend measuring base circles particularly if the lift is over about 0.550" but also to a lesser extent if the cam specs are 218 duration or over and if the LSA is tighter or the cam is advanced or retarded. The more the cam varies from the core the smaller the base circle will have to be.

Keep in mind this does nothing for the venerable "Hemi Tic" which is something entirely different but it will fix the problem if it is due to push rods being short from either small base circles or tolerance stack up or a combination
So in other words, use a proper pushrod measuring device to get the proper length.

Gotta hate those regrind cams with smaller base circles.
 

·
Registered
Joined
·
429 Posts
so a comp 260 with 6.1 pushrods means....????
 

·
Registered
Joined
·
2,196 Posts
Discussion Starter #10
So in other words, use a proper pushrod measuring device to get the proper length.

Gotta hate those regrind cams with smaller base circles.
The way the cores are provided pre roughed in you can end up with small base circles from new cores, particularly on bigger cams. That was the point of the equasion for the max base circle at a given lift. Thats also why 6.1 cams have a smaller base circle than 5.7 cams. 5.7 cam base circles wont work with much lift.
 

·
Registered
Joined
·
762 Posts
The way the cores are provided pre roughed in you can end up with small base circles from new cores, particularly on bigger cams. That was the point of the equasion for the max base circle at a given lift. Thats also why 6.1 cams have a smaller base circle than 5.7 cams. 5.7 cam base circles wont work with much lift.
I know exactly what you are saying. My point was to always use the proper tool and measure. Formulas are great, but checking in actuality is better. Nothing like a rocker falling off the valve stem tip due to improper geometry.

If I put together an engine with just using formulas and not using the measuring tools I have available to me, my boss would have me out on my ass faster than our customers engines propel their cars.
 

·
Registered
Joined
·
807 Posts
So, the Manley forged 5.7 pushrods I've got installed with my 260 cam are a little too short and might be the reason my HEMI is ticking so damn loud? Or are they just aggravating the excessive valve / valve-guide clearance already present on one of my exhaust valves?
http://media.putfile.com/HEMI-tick
 

·
LPG Hemi
Joined
·
2,785 Posts
OK Stu now please explain the Hemi Tick for us uninitiated please?;)
AL
 

·
Registered
Joined
·
807 Posts
I see some new pushrods in my future!:cool:
 

·
Registered
Joined
·
1,752 Posts
I know some of the custom cams have different base circles then the 6.1 cam. BUT,,, I thought the hemi tick problem was solved long ago.

Now what about the thousands of stock trucks that have it. ??? Did dodge make the push rods too short.?? It seams they may have. There is also the fact that the hemi has a louder valve train then a wedge style engine. But you have to look at the geometry of the 2 different styles of valve train. Hemi is louder, plain and simple. Is that the root cause of the noise?
 

·
Registered
Joined
·
2,196 Posts
Discussion Starter #17
All the aftermarket cams designed around the 6.1 1.540" diameter base circle. The post above explains why the 6.1 exhaust pushrod doesn't fully compensate for the 0.080" decrease in base circle when going from 5.7 to 6.1 base circle. Another issue is many aftermarket cams have a smaller base circle because the cores come roughed in and theres not enough material to get some grinds in with the cores provided without reducing the base circle. Thats why I measure the base circle on all the cams I get in and then make sure they go with the correct length pushrods if the base circle is infact smaller. Obviously, this is more an issue with bigger cams most of the stock block type cams aren't a problem.
 

·
All Around Great Guy
Joined
·
12,675 Posts
What length pushrods to use with 6.1 camshaft for no ticking
 

·
I RECOMMEND FUKKEN WAX
Joined
·
13,990 Posts
Stu is going to measure my new cam and send me the correct length pushrods.
 
1 - 20 of 31 Posts
Status
Not open for further replies.
Top