Milling/Shortening Cylinders

[yankee dog]

I have found lots of information on milling heads, but not much with regards to shortening cylinders?

I understand it is to boost compression ratio, and I have read about having the base of the cylinder milled and trued during a rebuild or a replacement of a leaky base gasket as a way to help eliminate the gasket leak from returning.

My question is, what other advantages are there to "shortening" the cylinder. Is there a reason to do a cylinder only and not the head? I know using thinner base and head gaskets boost compression ratios, so one can reason that shortening a cylinder can do the same. Is milling the cylinder shorter a way to use a gasket of relative thickness and still get a benefit of the compression boost?

I also read that milling a head can reduce the capacity of the chamber, so how does this play in to things. Is milling the cylinder a way to boost compression ratio (and squish) while not reducing the capacity in the head chamber?

If milling a cylinder, then how much is realistic for say a stock motor with a mild cam, free flowing exhaust and air cleaner? Mill the base AND where the head meets the cylinder? Base only?

I'm opening up a 1994 dyna due to base gasket leak, and planning on going with .020 base gasket, .030 head gasket, Vthunder 3010 cam. I want to true up the base of the cylinders and will go to the next size overbore if needed. So curious when I heard about shortening the cylinders say .010 but again, not finding much info.

The bike is currently stage 1,  cycle shack mufflers and k&n air cleaner, rejetted CV. 37,000 miles on the virgin engine.

Just trying to get a better understanding of the concept. YD

[kd]

Machining the cylinder (aside from trueing the surfaces) is usually to correct a piston deck height that is below the top cylinder surface. You have to measure that with the new base gasket in place.

[thumper 823]

Depending on combustion chamber mods usually turning dwn the cylinder is the way   (only way ) to achieve a tight squish.
Of all the mods you can do,  I think the best one is often overlooked.
A tight squish of .030 is the difference between ok and truly a great runner.

[98fxstc]

I have found lots of information on milling heads, but not much with regards to shortening cylinders?

I understand it is to boost compression ratio, and I have read about having the base of the cylinder milled and trued during a rebuild or a replacement of a leaky base gasket as a way to help eliminate the gasket leak from returning.

My question is, what other advantages are there to "shortening" the cylinder. Is there a reason to do a cylinder only and not the head? I know using thinner base and head gaskets boost compression ratios, so one can reason that shortening a cylinder can do the same. Is milling the cylinder shorter a way to use a gasket of relative thickness and still get a benefit of the compression boost?

I also read that milling a head can reduce the capacity of the chamber, so how does this play in to things. Is milling the cylinder a way to boost compression ratio (and squish) while not reducing the capacity in the head chamber?

If milling a cylinder, then how much is realistic for say a stock motor with a mild cam, free flowing exhaust and air cleaner? Mill the base AND where the head meets the cylinder? Base only?

I'm opening up a 1994 dyna due to base gasket leak, and planning on going with .020 base gasket, .030 head gasket, Vthunder 3010 cam. I want to true up the base of the cylinders and will go to the next size overbore if needed. So curious when I heard about shortening the cylinders say .010 but again, not finding much info.

The bike is currently stage 1,  cycle shack mufflers and k&n air cleaner, rejetted CV. 37,000 miles on the virgin engine.

Just trying to get a better understanding of the concept. YD

have a look at the Hayden pigtails

and all good advice so far 

[yankee dog]

Thumper and KD, thanks for the info, I am beginning to make sense of it. So deck height is the term I am looking for.

Is it safe to assume deck height is "variable" due to manufacturing tolerances with cylinders, rods and pistons? Or is it part of the design of the engine?

And the only true way to check "deck height" is to measure it with whatever base gasket (new) is going to be used, and to check the height under the specified cylinder torque load or just with the new gasket and no torque, maybe taking into account what the gasket manufacturer states is the "compressed thickness"?

So what is preferred deck height? Zero? What is preferred vs what is practical (is there a need to consider any margin for error or margin of safety) ?

Stock combustion chamber or maybe just a 3 or 5 angle valve job using the stock valves and .030 head gasket, and thumper 823, if I am reading you correctly, you like this method (shortening cylinders) to achieve a nice squish?

Pigtails, yes, read about them and the hayden oil fix, however, heard pigtails can reduce oil flow causing sumping, and I am wondering if the hayden oil fix can be used with say the cometic base gaskets?
Thanks again, YD

[thumper 823]

I know nothing of your pigtails, but you are getting tuned up on the deck Ht
You have to know what you working numbers are that is correct, so, yes, gaskets either have to have a known value  or waste a set
learning.
The deck ht is adjustable as required via gaskets or machining.
Harley off the assembly line will have as much as .070 for a squish ..if you want to call it a squish...(EvO)
I have learned this- Cast iron jugs are your friends.
They will not move or leak even without a gasket!  (Use yamabond or similar stuff)
You will get better ring sealing too.

[kd]

Thumper and KD, thanks for the info, I am beginning to make sense of it. So deck height is the term I am looking for.

Is it safe to assume deck height is "variable" due to manufacturing tolerances with cylinders, rods and pistons? Or is it part of the design of the engine?

And the only true way to check "deck height" is to measure it with whatever base gasket (new) is going to be used, and to check the height under the specified cylinder torque load or just with the new gasket and no torque, maybe taking into account what the gasket manufacturer states is the "compressed thickness"?

So what is preferred deck height? Zero? What is preferred vs what is practical (is there a need to consider any margin for error or margin of safety) ?

Stock combustion chamber or maybe just a 3 or 5 angle valve job using the stock valves and .030 head gasket, and thumper 823, if I am reading you correctly, you like this method (shortening cylinders) to achieve a nice squish?

Pigtails, yes, read about them and the hayden oil fix, however, heard pigtails can reduce oil flow causing sumping, and I am wondering if the hayden oil fix can be used with say the cometic base gaskets?
Thanks again, YD

Yes deck height is variable on manufacturer tolerance and you should have the gasket when checking it. It should be toque'd down to mimic the true install before you measure. If you don't have the gasket you can still measure and then put the gasket into your calc as if it was there. I was told  by  Cometic that their gaskets will not compress. I have found that to be true. I have found that using a thin coat of Yama Bond type sealer will not add to the dimension either. It squeezes out to a negligible seal.

Zero is the preferred deck height for most (myself included). It keeps the calc for compression easy and most head gasket thickness's (like Cometic) are usually based on zero deck when setting quench (squish thickness). ie .027, .030, .036 etc. As mentioned, the .030 head gasket is the sweet spot between good clearance and effective swirl production.

It is best if you have your heads done and cc'd first.  You can go to the Big Boyz calculator and enter your dimensions, deck and piston along with your chosen cam and cc's to find your compression. If you know what the best cc for your combustion chamber would be by fooling around on the calculator, you can have the head set for the correct compression when you get that work done.

Take your time and do the research. Search deck height measurement on this site and you'll find lots of good info. Chose a good porter like me of the vendors here and discuss your recipe with them. Be prepared to listen and take their good advise.

I don't really have a good response to your question about the "pigtails" or the Hayden oil fix. Is your 94 evo engine still a crankcase breather or is it a head breather.

[thumper 823]

Once you pass into the realm of understanding engine dynamics there is no going back.
Now you are a sick person on a slippery slope that no drug will cure.
let me tell you how this disease progresses.
At first, you will go to the machine telling them to bore the jugs to fit and perhaps a valve job.
Then like you, on the brink of destruction here, many will start buying their own measuring tools.
The is the next phase and not too noticeable.
The worst part is yet to come!
The fatal part.
Your understanding has gone from just assembling an engine and hoping it is all ok to to-
Buying the equipment like valve machines lathes, and the sort.
Your garage is running out of space.
As the disease progresses into the final stages-
You know you are terminal when where once your little red toolbox stood proudly, there is mostly a well-sorted machine shop.
No room for the simpler tools.
Your wife seldom sees you, and you lose sleep worrying about .ooo1 somewhere......
It's a slippery slope my friend ...
PUT THE MICROMETER DOWN!
Join the wannabee chopper gang and beer tasters cono sur tasting somewhere!

[kd]

   Yup   

[yankee dog]

Alright and thank you! I am now light years ahead of understanding this now than I was just a few hours ago. Thanks for the information, it's priceless!

The engine is a head breather, built one week before the manufacturing cut off as to when MoCo "officially" switched to the "correct cylinder studs" with the shoulder on the stud placed at the block (based on Harley TSB m-1043), so who knows...I will soon find out.

I have been to the Big Boyz calculator, but at that time I really didn't know what data I was entering, so it really didn't mean much to me, now I have a little more info/knowledge so will revisit it.

I did not plan on doing anything to the heads other than having them cleaned up and a valve job. Of course guides and springs replaced as/if needed.

Regarding trimming the cylinders, if removing .010 is the number, then should say .005 be taken from the bottom and .005 taken from the top to true up the base and the head surface? Or does the head contact surface of the cylinder get left alone unless there is an obvious problem and just the .010 gets removed from the base?

Lastly, which yamabond to use? I hear threebond is good as well and might even be the same stuff? I am a big fan of hylomar, but it is a non-setting type of sealant and I assume the yamabond is a setting type. I am willing to use what ever to get this sealed up right and not mess with it for a long while.

I suppose I can contact cometic about using the hayden oil fix with their gasket. I do know the hayden oil fix comes with their own base gasket (which I don't want to use) so If I do decide to go with the hayden oil fix, I will need to find out if it can be used with gaskets other than their own. YD

[thumper 823]

I can answer some of your questions
Yammy bond, not much,  enough to make at least a 1/16 th layer as it is all mostly going to get squeezed out.
Truing bases-
ALuminum rubber jugs - as for the Hrley ones- I hate them as they are a shifty bunch, that is why
they leak and I doubt you could get away with just Yammy or any sealer without a gasket.
Next Either one you would have to chuck up in a lathe or some sort of a fixture to check for being Sq and flat.
Albeit cast iron will hold its form, that is their inherent beauty.
I have a 1993 Evo non head breather and have not ever had a problem with it .
Clue me on this Hyden problem as I have oil cooler and no problems...

[Deye76]

With a tight squish, you have to warm the engine, no start and nail it behavior. If you have a .036 measurement, I wouldn't bother trimming the cylinders.   

[yankee dog]

https://www.haydensm6.com/tof_single.htm

http://foghollow.com/E-Shop/index.php?main_page=product_info&cPath=6_43&products_id=8163&zenid=5836097dfe1afa5b6b4fd23461d471a5

Personally, if I was to use one or the other, I am thinking hayden oil fix. But need to find out about using it with cometic gaskets.

As far as yamabond, the impression I got was to use it in conjunction with the cometic base gasket in a micro thin layer to each side of the gasket? YD

EDIT: Just came across this, so I thought I would toss it in here for others:

https://www.rbracing-rsr.com/squishcalc1.html

[98fxstc]

I used the yamabond and pigtails
no base gaskets
no problems

[Thermodyne]

https://www.haydensm6.com/tof_single.htm

http://foghollow.com/E-Shop/index.php?main_page=product_info&cPath=6_43&products_id=8163&zenid=5836097dfe1afa5b6b4fd23461d471a5

Personally, if I was to use one or the other, I am thinking hayden oil fix. But need to find out about using it with cometic gaskets.

As far as yamabond, the impression I got was to use it in conjunction with the cometic base gasket in a micro thin layer to each side of the gasket? YD

EDIT: Just came across this, so I thought I would toss it in here for others:


https://www.rbracing-rsr.com/squishcalc1.html

Get the Hayden kit that comes with gaskets, then just put a thin coat of three bond on them.  the paper is more forgiving than the steel core gaskets.  To use some other gaskets require drilling the holes out.

If you set the jugs in a torque plate you can measure how much the corners are rolled over.  Anything more than 010 can cause issues.  And the jugs are usually real close to correct length after cleaning the bases up.  The area between the studs is usually unchanged demensionally, its the corners that move down. 

Trock made a plate to dress them back into shape with valve compound, hard to find one still in used these days.     

[yankee dog]

Took things apart yesterday.

Cylinder stud collars are pointing up, and two of the studs came out with the head bolts. The threads on the studs that came out look fine, and the threads in the block look good as well. I separated the cylinder and piston (removed cylinder from piston, piston still on connecting rod) to get a better look at the threads in the block.

I figure I am having the cylinder bases trued up so the pistons need to come out of the bores anyways, and I will have bores checked to see if they need a hone vs over sized bore and then if pistons are needed I will have to further determine deck height with the new pistons.

I also plan on re-using the cylinder studs that came out. At this point, I plan on cleaning the stud and block threads with brake clean/brush and using red loc-tite and double nuts to install at the same length/depth as the others. I will look around for a ball bearing to install them but not holding my breath. I would love to replace the studs with new collar down studs, but I am not going to go looking for trouble.

Anyways, uneventful disassembly otherwise. I like uneventful. YD

[Thermodyne]

Took things apart yesterday.

Cylinder stud collars are pointing up, and two of the studs came out with the head bolts. The threads on the studs that came out look fine, and the threads in the block look good as well. I separated the cylinder and piston (removed cylinder from piston, piston still on connecting rod) to get a better look at the threads in the block.

I figure I am having the cylinder bases trued up so the pistons need to come out of the bores anyways, and I will have bores checked to see if they need a hone vs over sized bore and then if pistons are needed I will have to further determine deck height with the new pistons.

I also plan on re-using the cylinder studs that came out. At this point, I plan on cleaning the stud and block threads with brake clean/brush and using red loc-tite and double nuts to install at the same length/depth as the others. I will look around for a ball bearing to install them but not holding my breath. I would love to replace the studs with new collar down studs, but I am not going to go looking for trouble.

Anyways, uneventful disassembly otherwise. I like uneventful. YD

Just buy 8 oem studs and install them bead down.  Reusing 30 year old studs is not advisable, especually when they all need to come out and be installed bead down.  Studs are way too inexpensive to mess around with used ones.  Last set I bought was like $41. 

[yankee dog]

Took things apart yesterday.

Cylinder stud collars are pointing up, and two of the studs came out with the head bolts. The threads on the studs that came out look fine, and the threads in the block look good as well. I separated the cylinder and piston (removed cylinder from piston, piston still on connecting rod) to get a better look at the threads in the block.

I figure I am having the cylinder bases trued up so the pistons need to come out of the bores anyways, and I will have bores checked to see if they need a hone vs over sized bore and then if pistons are needed I will have to further determine deck height with the new pistons.

I also plan on re-using the cylinder studs that came out. At this point, I plan on cleaning the stud and block threads with brake clean/brush and using red loc-tite and double nuts to install at the same length/depth as the others. I will look around for a ball bearing to install them but not holding my breath. I would love to replace the studs with new collar down studs, but I am not going to go looking for trouble.

Anyways, uneventful disassembly otherwise. I like uneventful. YD

Just buy 8 oem studs and install them bead down.  Reusing 30 year old studs is not advisable, especually when they all need to come out and be installed bead down.  Studs are way too inexpensive to mess around with used ones.  Last set I bought was like $41.

It's not the cost of the studs or the time. It's the "if it ain't broke" mentality. I'm leaving them collar up and installing the two that came out collar up. The bike has done fine to this point in it's life with the collars up. The last thing I need is to have the block threads come out when removing the studs that don't need to be removed...

Yes, I'm taking the easy way out by just putting those two back in but again, I don't want to go asking for trouble.

Replacing the studs might not seem like a big deal, but all the threads I have read about people having problems with those studs just makes me want to leave well enough alone.

I am sure there are plenty of evo's still on the road with collars up and running just fine.

So unless there is some big advantage by changing them, or I am grossly missing something, I am leaving well enough alone. YD

[kd]

Used studs have already been stretched. That's what the torque spec is supposed to do. Sometimes you can reuse them, but you already have evidence of problems with 2 of them. The early years were a problem, that's why they changed. Continually retorqueing can cause over stretched and stressed studs that can break. Try getting a barrel off in the chassis when a stud breaks below the head gasket surface.    How many times have they been retorqued.  It's probably easier to patiently remove the survivors and replace the than it would be to tear it down again and replace all the gaskets and do the work. You'are right though. It's your call.   

[Don D]

Be very cognizant of the threads. EVOs pull. You can feel it when torqueing the bolts.

[Thermodyne]

New studs are elastic.  As in they give a little when you tighten the nuts down.

Used studs are brittle from all of the heat cycles they've endured.  So they dont give when you tighten the nuts.  But those aluminum threads are happy to step in and give a little.  And after they give it up the first time, they will give it up easy the next time.  And soon enough they give up completly and pull out.  Next time could be from the next rebuild, or it could be after a few heat cycles.

[14Frisco]

Be very cognizant of the threads. EVOs pull. You can feel it when torqueing the bolts.

If one can "feel it when torqueing the bolts", then one won't be able to apply the correct torque, right?
Thus, if one can apply the correct torque then the threads are ok (for the time being)?

Is there anything else one can do, but to try to torque, and if it works, it works?

[kd]

Be very cognizant of the threads. EVOs pull. You can feel it when torqueing the bolts.

If one can "feel it when torqueing the bolts", then one won't be able to apply the correct torque, right?
Thus, if one can apply the correct torque then the threads are ok (for the time being)?

Is there anything else one can do, but to try to torque, and if it works, it works?

I think what Thermodyne is saying is, when you are torquing the fasteners, if the threads are pulling (because the elasticity is used up in the studs) you will feel it because the torque limit won't be able to be reached. The stud will pull from the case threads usually very near the torque spec. As you said, If the stud does not pull and the torque limit is reached in safety, the risk remains afterwards when the studs are subjected to further stretch caused by the expansion in the length of the cylinders (of approximately .060) when they heat up to temp. They may only be good for the time being.

The problem with this scenario (and to respond to your last question) is, if they do "pull" because the studs are fatigued, or later for the same reason, it will be too late. The cases are now damaged and will require a repair. You start over, or more properly said, you will be 2 or more  steps back from where you are now.

I think we are all singing out of the same hymn book.     

[Ohio HD]

I sold and installed a lot of Evo S&S cases between '90 and about '96. Late 80's and earlier 90's HD cases had issues, porosity, studs pulling out, deck surfaces not square or flat. I think they had some many bikes in demand, they had anyone and everyone making cases and heads.

[FSG]

studs are cheap and changing them all now is the best option, certainly cheaper than the alternative IMO

[Hillside Motorcycle]

The studs aren't/weren't the issue, but rather the poor quality case material, usually casing a fracture in the 90* corner behind the rear tappet block, migrating up to the cylinder stud holes, and in other instances, the cylinder stud case threads are only pulled.

[thumper 823]

Unless you have a well-rounded education in metallurgy, one will scoff at fastener stretch.
It is real folks, and like already said -once the rubber is gone,  the steel it is now just a static pull and quite worthless.
If seeing is believing, walk into a "Reliable "  diesel shop and ask for head bolt stretch gauge and used head bolts.
They should have an ample supply. You can actually see how far a bolt will stretch.
I have found it is much cheaper to replace strategic fasteners then even take the time measuring them.
Do you want to replace threads in the case?
Or the studs.
Personally, I use a brand name with a great reputation.
I HATE redos.

[Deye76]

"I have found it is much cheaper to replace strategic fasteners then even take the time measuring them."

I never understood guys spending 12-15 hundred on a flywheel assy., another 6 or 7 hundred on cylinders/pistons, then another grand on heads & cam, only to cheap out and reuse fasteners.

[HD/Wrench]

I sold and installed a lot of Evo S&S cases between '90 and about '96. Late 80's and earlier 90's HD cases had issues, porosity, studs pulling out, deck surfaces not square or flat. I think they had some many bikes in demand, they had anyone and everyone making cases and heads.

I feel the largest issue is the case.. I know that they can create issues. If the stud is not rusted I leave them alone. been down the road of replacing them only to have them pull right out of the case. Install tyme sert  yep it pulls that out as well . For what ever reason many times I feel you are better to leave them alone .   If you get to that point , time for a set of S&S cases and move on.

The case issue ran for years and as already stated common for this issue and then as Scott pointed out the case cracking behind the tappet block.. Lost count of how may came in for gasket repair for a leak and its the case that is cracked ..

HD studs are pretty tough all in all and not a common issue to have one break . at least not as common as the stud pulling out of the case .   Slippery slope for sure

[thumper 823]

Like all things they stretch and wear out
The bolt / studs, loses its elasticity and becomes a static pull over time or just shears off.
It is good practice to replace them if in doubt

[farmall]

If you damage the case threads, threaded inserts are cheap and an upgrade, hence their use on aircraft with much higher time between overhauls than motorcycle engines. Skip coil inserts and use a barrel insert instead. There are quite a variety and many are designed to install using a standard tap. Tape off with painters tape (clean with contact cleaner first so no oil prevents tape adhesion) and no chips will go in the engine.

McMaster-Carr, MSC etc industrial suppliers have many examples, but I'd use them to find the part then search maker and part number or name to save money. The big boy industrial suppliers serve the "need it NOW" market which can't afford to wait and price accordingly. Their excellent catalogs make great bathroom reading...

[thumper 823]

What is the installed thickness of Hayden gaskets?
I looked at their page and no specs.

[farmall]

I got a Hayden kit and the brass tubes (AKA pigtails but I've never seen a hog with a tail like that!) are the important part. They sell gaskets with the kit to avoid owners having to punch holes in a stock gasket.

You can use the Hayden gaskets as templates with a Sharpie to mark other gaskets then punch holes as you prefer.