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cylender head problems...
https://slantsix.org/forum/viewtopic.php?t=37386		 Page 1 of 1
Author:  theslantingsix [ Mon Oct 05, 2009 4:22 am ]
Post subject:  cylender head problems...
i'm having my head on my car built finally. but now its to the point for shaving the head and the machinist says the max he will take of is .045 thousanths (i want to go .090 off the head for high compression) because of some kind of push rod rocker geometry or something. well he wants to charge me 100 bucks to shorten the push rods (i don't really want to pay it because i got to much money in the head already) so my question is should i get my push rods shortened, or is there enough adjustment in the rocker arms that i can get by with it
Author:  dakight [ Mon Oct 05, 2009 5:03 am ]
Post subject: 
Every motor is a little different. You may need to shorten the pushrods or you may not. If there's enough thread on the adjusters you can get by without cutting the pushrods, but geometry will be off. The engine will still run ok. If you run out of thread on the adjusters before you get to the proper running clearance then you will have to shorten the push rods. Even if you can get the correct clearance to start, you may find that later on you won't be able to properly adjust the valves as everything wears in.
Author:  66aCUDA [ Mon Oct 05, 2009 6:05 am ]
Post subject: 
Remember this isnt a V8. Every slant I have seen you could take .100 off deck/head combined and still run stock push rods. When you get to .150 is when it seems to get necessary.
My machinest had a fit the first time than I told him to take .100 off the head and .050 off the deck and bore to .080 over. I told him do it or I will find a new machine shop. He is now convinced... as he has been for a ride in the car with that engine.
Frank
Author:  armyofchuckness [ Mon Oct 05, 2009 6:56 am ]
Post subject: 
My machine shop guy tried to tell me I needed to shorten the pushrods too. I have yet to see anywhere where anything .100 or less needed shortened pushrods. Took forever to convince him it'd be fine.
Author:  Charrlie_S [ Mon Oct 05, 2009 9:02 am ]
Post subject: 
The first 170 engine I did, required shorter pushrods, when the head was cut .100. That is the only one. Also, even if you need shorter pushrods, I think Smith Bros. will make whatever length you need for less then $100.
My opinion on machine shops: If I want something done, that they don't agree with, I do like them to tell me, and state why. Then it becomes my decision as to what gets done. If the shop doesn't want to do it my way, I would go to a different shop. IT IS MY MONEY.
Author:  Krooser [ Mon Oct 05, 2009 9:32 am ]
Post subject: 
Ditto on they other guys said...
Author:  Doc [ Mon Oct 05, 2009 10:11 am ]
Post subject: 
I have an engine with a combined .220 milled off the head & block and it is still using stock length push rods. :shock:

The adjusters on this combo are "wound-out" more then I like to see them but I was able to help that issue, as well as rocker tip to valve stem contact "swipe" pattern by using some .060 rocker shaft shims. (move the rocker shaft higher off the head)

I may break-down and buy a set of shorter pushrods for this engine, just because the rocker arm ratio is better (higher) when the adjuster screw is deep in it's adjustment socket.
DD
Author:  Dolmetsch [ Mon Oct 05, 2009 6:46 pm ]
Post subject: 
Being my own machinist I never have that problem although since i sold my equipment I do have to suckhole occasionally but what you were told is right. If he argues with you go elsewhere ,immediately.
The great Austrian Artist , Andre Heller father of the modern light shows once said.
"The person saying it cannot be done should not interupt the person doing it. "
If the geometry is really off( and I doubt that it is even really an issue) You can shim the rocker and set the stem heights higher. If the stem heights in the head are already set then you could use lash caps.
Now when you ask your machinist what he set the stem heights at he is going to look at you funny cause he is a chevy man and hasnt the faintest idea what you are talking about.
Carry on , you will be fine, you'll see. These are a couple of good options if it is a big problem . I have also though done several motors and did not have a pushrod issue despite the big cuts. You can get anal here. You certainly dont want something that will fly apart but factory tolerences being what they were when these motors were built sometimes the geometry is better when the cuts are made than it was stock.
Don
Also many hi perf cams have a smaller basecircle than the stock cam which buys you some more pushrod length. Why ? Because most cams have the same height of lobe . The extra lift comes from the DIFFERENCE between the base circle and top of the lobe, not by making the lobe higher. If we made the lobe higher the cam often wouldnt go into the engine because the lobe would be higher than the cam journal bearing surface. As you can see there are a lot more issues at play than just what you machined of the head. I would check to see if it is in the acceptable range which means with in reason and leave it at that. I have seen guys spend $1000SSSSSS fooling with stuff like this gaining maybe at best 1 to 2 hp and wasting months while the rest of us are out cruising and racing.
Author:  slantfin [ Wed Oct 07, 2009 12:37 am ]
Post subject: 
Quote:
"The person saying it cannot be done should not interrupt the person doing it. "
8)
Quote:
The extra lift comes from the DIFFERENCE between the base circle and top of the lobe, not by making the lobe higher.
Ah. This answers a question I've had for a while about how you can regrind a stock cam to get higher lift. :idea:
Author:  theslantingsix [ Wed Oct 07, 2009 4:37 am ]
Post subject: 
thanks for all the help guys, this was kind of a a learing expericne building my first slant hope it runs good

by the way doc what kind of compression are you running on the .220 milled off the head and block
Author:  Doc [ Wed Oct 07, 2009 8:41 am ]
Post subject: 
Quote:
...by the way doc what kind of compression are you running on the .220 milled off the head and block
That engine is one of my "old solder" race engines, it's the first stroker - long rod engine I built. Ran at 13 to 1 when I was trying to get a squash/quench situation to work. (

That engine block is the one shown in many of the SL6 Block prep article photos and it has lived a hard life... it currently has .130 off the block deck, it has two cylinders sleeved, is at 3.485 bore and was eventually "detuned" and put into the "back-up engine " pool.

As for a stock stroke 225, at .060 overbore (3.460) with .220 off the deck and head, that would give you somewhere around 14 to 1 compression.

The way I was able to get this block back into a "pump gas" compression ratio was by using shortened 2.2 pistons with a dish.
DD
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