Quench-Again.

['68falconohio]

I know this has been discussed previously and I've searched the internet and the forum for rock-solid answers.

I'm building a 200 six with a highly modified log head(no log) for my daily driver. 15k miles/year.

My pistons are sitting .005-.010" in the cylinders(deviation due to stock components, didn't go through trouble of matching them) and I would like to use an OEM gasket for several reasons.

1.) improved quench/squish.
2.) I'm unshrouding valves so combustion chamber is growing.
3.) I want to leave as much meat on the head as possible.

This puts me at .030-.035" of static clearance between the cylinder head and top of piston(dished pistons with 5cc dish). Speaking with the engine builder that did my work previously, he said .035" will be tight and less could cause the pistons to kiss the head. I'm leary.

I'm not going to do any more cutting on the block. The engine is currently in my car and I'm 'only' going to swap in the head and related components once I have it finished. I had full rebuild 10k miles ago, which included a direct mount 2V head.

My goal CR is 9.3:1. Utilizing smoother combustion chambers, a good quench, and proper timing curve. I want to run on 89 octane. The combustion chambers of my E0 cylinder head are ~62cc prior to unshrouding/smoothing so I will have to do some substantial cutting on it to get my CR up.

I have a line on an OEM gasket for the 200 but don't want to get something that I can't use, and more importantly, don't want to my engine to scatter if the head to piston distance is too tight.

Anyone have links/info they're willing to share on quench. I've read CZLN6's posts on quench distance throughout the forum, and he has said .030-.035" would be ideal. I'm at a loss as to who to believe. I have great respect for CZLN6's contributions to us sixers and also great respect for the engine builder who told me <.035" could be too tight.

All suggestions/knowledge are greatly appreciated.

 

[rbohm]

8) to get an idea of how large .035" is, look at the stock plug gap for the small six. unless you are using aluminum rods .035" is plenty of clearance between the piston and the head. heck we ran even tighter clearances than that with aluminum rods in our fuel altered many years ago, as do many circle track racers that run aluminum rods. with a zero deck and a .025" thick head gasket and no evidence of the piston hitting the head even turning 9000 rpm for 200 miles.

 

[CZLN6]

HOwdy 68Falcon:

The variable in your build is the cam timing. To be mathematically and theoritically safe, after all is said and done you will need at least .120" piston to valve clerances for the exhaust and .100" for the intakes, assuming all parts are fitted and tight. The only way that I know of to make sure you have safe clearances, before the fact, is to measure. This means assembling the head, place some clay on several piston tops, install the head solidly with maybe four head bolts, adjust the valves to snug and then slowly turn the engine over several times. Take the head off and measure the thickness of the thinnest part of the impressions the valves made in the clay on top of the pistons. We've done this with the gasket to be used torqued into place, as well as with no head gasket at all, simply to save a little work and time. As you rotate the crank assemble, if you get a tight contact you may have to redo the process with the gasket in place. IF you decide to do it with a gasket in place, the gasket can be reused so long as the engine is not run with it.

Also, do not overtighten the rocker arms as the dry lifters will simply collapse the spring inside. Are you using adjustible rocker arms? Measuring the thickness of the thinnest part of the clay is a bit tricky too. You might try slicing the clay through the middle of the valve mark and measuring the profile. Also, cooler clay is a little less likely to deform as it is removed from the piston top. A slight coating of a light oil also helps to remove the clay impression from the piston top.

I hope this is clearer than mud, but the only was to get rock solid information on your project is to measure for yourself. My guess is you will have lots of clearance with stock type dished pistons, but for your peace of mind and mine I would encourage you to measure for yourself.

Let us all know how the process goes and what you learn.

Adios, David

 

[CNC-Dude]

Are you personally checking the deck on the engine yourself. If so where on the piston are you checking the deck clearance. You might already know this, so i'll mention it for those that might not be aware of this. Many people incorrectly think that the center of the piston is the ideal place to check the deck height. You actually need to check the piston on the spark plug side of the piston and on the quench side as well. Once you find TDC for the piston, move your dial indicator to either side, and then rock the piston away from you and then toward you, taking the reading in each direction and then averaging the two readings will give you the deck clearance for that side of the piston. I have had Super Stocker pistons bump the head with .030 piston/head clearance. You will quickly see that with the deck at -.005 or -.010 at the center of the piston, that the piston can actually rock above and out of the top of the cylinder on the sides, coming even closer to the head. So -.005 in the cylinder at the center of the piston isn't the same as -.005 on the quench or spark plug sides....big difference. For instance, if the piston rocks +.010 out of the cylinder in one direction and then -.005 in the cylinder in the other direction, the average deck clearance is +.0025 out of the cylinder, while the center of the piston can still be -.005 in the cylinder, thats a differance of +.0075. You see where you can start to get into trouble if you don't use the correct procedure to check the deck clearance. So you would need to cut that side of the piston .012 to get it to be -.005 in the hole. Ideally, .035-.045 is a good number to have for your piston/head clearance, so find something in the middle that makes you and your engine builder comfortable.
More food for thought, if you are plannng to twist the engine up occasionally for a blast down the road, remember that at 6000 RPM, each piston makes 100 complete revolutions per second. If you run the clearance too close, the damage will be done long before you can even react.

 

['68falconohio]

rbohm, David, and CNC-Dude: Thank you. Now to ask more questions.

The variable in your build is the cam timing. To be mathematically and theoritically safe, after all is said and done you will need at least .120" piston to valve clerances for the exhaust and .100" for the intakes piston to valve clerances assuming all parts are fitted and tight.

Why do I only need .012" piston to valve clearance when I need .030"-plus clearance for piston to head? If the piston to head clearance can shrink that much can't the piston to valve?

My single pattern camshaft only gives .420" of lift with 208* @ .010". It's small from a performance standpoint but has given great economy with my current setup(I still have stock exh. manifold to boot).

I've been lurking on speedtalk.com for a while and have read the clay method for chekcing valve to piston interference along with cross sectioning the clay for ease of measurement. I fully intended to check for clearance prior to startup.

Are you using adjustible rocker arms?

At this time, no. The threads per inch of the rocker pedestals and turns of bolt were used to calculate the lifter preload. My rocker pedestals are shimmed to accomodate the cutting that was done on the current head and block. I want to change to adjustable to eliminate shimming. By finding either a cheap set of 1.5:1 adj. or buying a set of roller-tipped 1.6:1's. I'd like to have full roller 1.65:1's but I'm not going to have my bottom end apart in the near future to get the chips out that are caused when tapping/plugging the oil galley to the rocker pedestal, which is required for the full rollers.

In my head, it seems by changing to a higher ratio rocker, I can simulate a steeper cam lobe profile, correct? This would seem to be beneficial for my daily driver, torquey motor?

Are you personally checking the deck on the engine yourself.

The deck was checked by the engine builder before the engine was assembled and put in my car. Before this rendition of my 200ci will have a head put on, I will check all of the pistons with a dial indicator. Rocking them both ways to be certain. I'll have to give him a call and ask him how he measured them. He's been helpful with my quest for knowledge as well as everyone on this board.

Ideally, .035-.045 is a good number to have for your piston/head clearance, so find something in the middle that makes you and your engine builder comfortable.

Are you saying .035-.045" of clearance between piston and head between the piston at the pistons' highest point(side rocked up)?

If you run the clearance too close, the damage will be done long before you can even react.

That's what I'm afraid of. I'm trying to figure all of this out before I get to the point where I take a week off of work and put this thing together. Shooting for next year sometime, haha.

 

[CNC-Dude]

Yes, .035-.045 from the pistons highest point. As for the P/V(piston to valve)clearance, i'm sure that was a typo, and he meant .100 or .120, which is more adequate. Also, the valves need to have about .050 clearance around the diameter of the valve in the piston as well. You will make the cutter .100 larger diameter than the valve to achieve this. If using a degree wheel to degree your cam in, and you should, you can stick an indicator on each valve to measure how much P/V you actually have, using the clay method can sometimes be deceiving, especially when using a hydraulic lifter to do this, it can collapse internally before the valve fully presses into the clay. Also, keep in mind that TDC is not the point at which either valve is closest to the piston for checking this, and also advancing or retarding the cam changes your P/V for each valve.

 

[drag-200stang]

I have never put one of these things together that had a piston to valve clearance issue. I have put .125 pop up pistons with wild cams, with 0 decks and .070 off the head and still no clearance issue. Should not be an issue to worry about, but always check.

On the piston to cylinder head clearance I could tell you if you do this, it will just kiss the cylinder head.

C3 forged rods, 450 gram forged pistons, forgot pin weight, 0 deck piston, checked at center with .0055 skirt clearance, steel shim gastket (keep in mind these run from .017 to .025 - they vary). I ran one that was about .022. Engine was shifted at 7500, missed shifts would go to 8000. Number one piston showed signs of hitting the head on teardown. So for a milder street engine with rev limiter I think that .030 and up would be safe. This was on a 200 engine.

 

[gb500]

have aread of falcon 60's posts where he set his 200 up with 35though quench - no problems

viewtopic.php?t=38301&highlight=

may help you

brett

 

[CZLN6]

Howdy Back All:

"As for the P/V(piston to valve)clearance, i'm sure that was a typo," Yes, Good Catch CNC dude mean. But CNC dude raises another good concerns on using the clay method with hydraulic lifters. Hyd lifters can collapse while measuring with a dial indicater as well. However most don't have a set of solid lifters to use on pre-assembly. He also noted that the closest point between the valves and the piston does not take place at TDC, but X degrees after.

On quench effect and clearance, when deck clearance gets to .045" and greater the efficiency of quench lessens. The idea of a tight deck clearance is to generate a robust quench effect.

Given your engine design, I doubt that you're anywhere close to catastrophic clearances, but it is alway a good idea to pre-assemble and to measure for yourself, to be certian.

Did you degree the cam upon installation? What setting? retarded? or Advanced? Do you have access to an accurate dial indicator set up with which to measure.

With a mild cam and hydraulic lifters it is not necessary to shim the rocker shaft staunchions. Hydraulic lifters can accomodate up to .125" differences in wear, machining and parts mis-match.

Q- "Why do I only need .012" piston to valve clearance when I need .030"-plus clearance for piston to head? If the piston to head clearance can shrink that much can't the piston to valve?
A- Piston rock on the wrist pin, rod stretch and bearing wear are all variables with piston to head clearances. These will all increase with time, wear and higher rpms. The valve, if well controlled, will grow less, however valve float can occur with Hyd lifters.

Q- "I can simulate a steeper cam lobe profile, correct? This would seem to be beneficial for my daily driver, torquey motor?"
A- Yes, and Yes. However, getting more cam lift by increasing the rocker ratio puts more stress on all valve train parts, usually requires more valve spring to control the valve movement, increases rocker tip to valve tip geometry criticality, and adds side load wear to valve guides. In general, it is best to add more lift in selecting the cam in the first place. The ideal place for adjustible 1.6:1 rocker arms is in a mostly stock upgrade, bolt-on where the block is in good shape and the owner does not want/or forsees any block rebuilding in the future. Now, the adjustible feature is worth having to be able to easliy adjust the pre-load on hydraulic lifters.

Keep it coming. I'll be very interested to hear what you get for final P/V and deck clearances.

Adios, David

 

[CZLN6]

Howdy Back All:

And pass the crow!!!! I was wrong The correct p/v clearances on our engines should indeed be least .120" piston to valve clerances for the exhaust and .100" for the intakes. Wouldn’t it be nice if whenever we messed up our we could simply press “Ctrl Alt Delete” and start all over? AMEN!!! I guess this is the next best thing- admit it, apologize and edit! My apologies. Thanks again to CNC dude for pointing it out.

I have edited out all the wrong dimensions and inserted the correct ones. I hope it did not lead anyone astray in the wake-up time.

Another bit of infor from the Comp Cam catalog is a generality that a cam with under 230 degrees of duration at .050" lift will have sufficient p/v clearance about 98% of the time. that other 2% is why we mock up and pre-measure.

Adios, David

 

[CNC-Dude]

David, I know that you knew the correct specs. Sometimes when we try to answer two or three different questions in the same post, we know what we want to say, it just doesn't make it to our fingertips to type it out. You are probably like me, in that I will go back and reread what I post several times, and I thought you would see it. I know people do ask advice because they have a true desire to have that knowledge. And I want to make sure that I can give info that is as accurate as possible so they don't potentially have issues because of something I told them. Good job.

Scott

 

[MustangSix]

As you measure also keep in mind that the PV distance is not always the closest at TDC. The valve usually is opening or closing as the piston approaches the combustion chamber and max valve lift doesn't always occur at TDC.

 

['68falconohio]

Thanks Everyone, More Questions

CZLN6,
I want to use the OEM gasket for more than quench, and I know the replacement gaskets out there pretty much kill all quench effect unless you set the piston up at zero or a little above the deck. My biggest concern is going to be getting a decent CR. 9.3:1 is my goal and I'm not sure how much material I"m going to remove to unshroud the valves thus causing a lot of shaving of the head. I'm strongly considering leaving the stock size valves in my E0 head and just unshrouding them versus making them bigger and not being able to unshroud them as much. OR just upsizing the exhaust valves only because the exhaust is poorly matched to the intake flow-wise. I don't know what would be better and eventually I'm just going to make an educated decision and roll with it.

I know it's been said on this forum that .090" can be shaved off a head depending on what's been done in the past but I want to leave as much material there as possible. I can have UT(ultrasound testing) of the head to determine thickness done for next to nothing(beverages) but I want to save the drinks for me.


Q. Did you degree the cam upon installation? What setting? retarded? or Advanced? Do you have access to an accurate dial indicator set up with which to measure.
A. The cam was degreed in my current build and set 4* advanced. Yes, I have access to accurate dial indicators and mag. stands. They're harbor freight jobbies but have been checked on calibration blocks. They're decent.

Q.With a mild cam and hydraulic lifters it is not necessary to shim the rocker shaft staunchions. Hydraulic lifters can accomodate up to .125" differences in wear, machining and parts mis-match.
A. Yep, the only thing I was warned about was extra pre-load causing premature valve float or valves stuck-open. I sucked it up and paid the engine builder to check and shim accordingly. He strongly advised me to either check them myself(I didn't know how and didn't have the time due to school) or have him check and shim accordingly. I had him do the deed, a small price in the grand scheme.

Thanks again,
Stephen

 

[CZLN6]

Howdy Stephen:

I'm reluctant to offer any more advice while my mouth is still full of crow, but..... I can't help myself. My recommend would be to go with 1.5" exhaust valves, back-cut the intake valves and do minimal clean-up and polishing of the E0 chambers. If you do any unshrouding, focus on the intake side alone and be sure to not go beyond the bore of the cylinders. There is room to work with on the high side, but don't overdo it. The problem is that you can't use a cutter to get this done. It is a by-hand job. If you do this you really should cc measure each chamber to ensure they are all the same volume.

Where did you find an OEM head gasket? FYI- they are thinner, but they don't seal nearly as well as a modern composite gasket.

Keep it coming. (PS- I love Harbor Freight)

Adios, David

 

[rbohm]

8) david, try egge.com for stock type head gaskets for the small six. they specialize in vintage parts.

 

[CZLN6]

Howdy Back:

The last time I checked with them, over a year ago, they didn't have any for a 200/250. I have several that I bought from Greg (aka FTF) many years ago, but they are my private reserve and not for sale.

I was recently told by an engine builder that he reused an OEM steel shim gasket that was in good shape appearance wise. He painted both sides with a silver metalic spray paint and bolted it on. He said it worked fine, with no leaks or problems. He's somewhere in the inland Empire area of SoCal so I don't have a current update. I hate to pass on hearsay as gospel. Has anyone actually done this???? What were the results???

Adios, David

 

['68falconohio]

David,
I posted a wanted add on the forum and a fellow member sent me a PM. I hadn't bought the head gasket yet and have decided not to at this time. I'm going to have too much time and money in this cylinder head/engine build and being that the falcon is my only ride at the moment, I just can't risk it. I'll go with the thinnest replacement gasket available and build from there.

I was leaning towards just up-sizing the exhaust to 1.5". I don't think I'm going to unshroud the intake valves since I'm not using an OEM gasket, I need to retain the smallest combustion chamber possible if I want to get any compression out of this head.

On the backcut of the intakes, 30*?

I don't know if you've seen this thread, but THIS is the head I'm working on. I'm going to post more questions on that thread as they don't pertain to quench/squish.

And oh yeah, Harbor Freight(China) has an extremely wide variety of inexpensive tools. For light duty, I don't think they can be beat.

Thanks,
Stephen