Topic: Thicker Head Gasket CB550 Math

[KV41]

SOHC,


I am in kind of a pinch and it looks like I will either need to get a new head or figure out how to make up for the difference in head and base gaskets.

Who ever was in the motor before I received it had decked the head leaving unacceptable scoring in the surface. I took it to my machine shop and had them re deck it. From what I have figured out my head measures 3.366(85.49mm) thick (from valve cover gasket surface to headed gasket surface) and from what I have gathered from other posts on here stock heads measure 3.4015 (86.4mm).  I measured a stock head gasket and base gasket and found the head gasket measure .050 and the base .020.  These are new and not compressed gaskets. Here is the math I used to figure this out. I may be completely off for doing it this way. Let me know.

STOCK
3.4015 (Stock Head Thickness) + .050 (HeadGasket) + .020 (Base Gasket)= 3.471

MY HEAD
3.366 (Current Head Thickness) + .050 (HeadGasket) + .020 (Base Gasket)= 3.436

GAP NEEDED TO BE MADE UP
3.471 (stock) - 3.436 (My Head) = 0.035

So it looks like I need to close up a .035 gap with some gaskets if they make them. I did find a .060 headgasket and it looks like its the thickest gasket I have been able to find. That said that brings the gap down to .025 so I went looking for thicker base gasket with no luck. Ideally a .065 head gasket and a .040 base gasket would work. Please let me know your thoughts.

Thanks,

Kyle



 
 

[low-side]

Coppergaskets.us can make a number of thicknesses on head or base gaskets.  I've used their gaskets on several bikes.  Very high quality stuff at very reasonable prices.

[bryanj]

Dont forget if you use a thicker gasket you need thicker O rings

[KV41]

Thanks! I just sent a email to them.

I have never used copper gaskets. Would it be a good idea to split the .035 gap I have between the gaskets? Also, is there a downside to using copper gaskets?

[Tracksnblades1]

Kyle have you measured your piston deck height? 
Without piston rings would speeds things up while selecting
Base gasket combinations. Positive (above deck) or Negative ( below deck). .?
While your looking at gasket thicknesses, I would aim at
achieving the best (squish) piston to cylinder head clearance.
Since your already crunching numbers...

I'm not a 550 guy. But, wouldn't you just have a little more compression
from reduced combustion chamber volume due to cylinder head machining?
Or does a 500/550 require a specific cyl head thickness.?
Am I missing your goal...?

[strynboen]

make a thik deck/base gasket...to lift the head..and cylender block..or stack some base gaskets to make the korrekt thikness
as bryan is inn over..thek the o rings ..they need to be sqveesed a bit..so a over seize is needet

[calj737]

I have a different view on your situation. Head gasket thickness is truly only a concern for valve-piston clearance. Stock, you have ample clearance even with the decking that has occurred that you should not need a thicker than stock gasket.

Decking does require that you also trim the locating dowels between the head and deck to allow the head to seat fully.

Your best course of action is to dry assemble the head, use machinist's clay, install the cam, and rotate the motor by hand to check for clearance issues. If there are none, use whatever gasket you need to obtain a minimum clearance (0.032) between the head and piston.

Decking should have slightly increased the compression (as was stated) without compromising the clearances.

[KV41]

calj737,

My only concern with that is the bump in compression and also at what point will the timing be retarded because the complete head/cylinder assembly has shortened a tad bit. What will the benifit/downside of a higher compression ratio be?

Thanks,

Kyle

[calj737]

Completely negligible change in compression. I doubt timing will even be retarded as a result.

If you are concerned about that, you can install a slotted cam sprocket to adjust timing based upon actual TDC.

[Tracksnblades1]

Completely negligible change in compression. I doubt timing will even be retarded as a result.

If you are concerned about that, you can install a slotted cam sprocket to adjust timing based upon actual TDC.

Good points,

The decking would retard camshaft timing a bit, due to the cam being chain driven.

The correct "squish" piston to cylinder head generally procures a more efficient chamber requiring less ignition lead.

 KV41 could use a pair of light springs under the intake/exhaust valves with a dial indicator to determine valve to TDC piston clearance. It wouldn't be as accurate as a clay measurement unless you checked every degree of rotation during overlap lift at TDC.

I agree I don't see why the head can't be used again.

[seanbarney41]

I don't think the o.p. is worried about cam timing.  I think he is worried about having to retard ignition timing to prevent detonation/pre-ignition caused by increased compression.

I don't know what the 550 can withstand in this regard.  I do know that 750 performance pistons are gonna add more compression than that amount of cylinder head thickness loss would, and many end up running the stock ignition timing curve with good success.

[Tracksnblades1]

Agree,

Not knowing the OP's aptitude in engines, my inference was merely to remind that the camshaft would be in a slightly retarded position.

Most engine tuners know retarding the camshaft delays intake valve closing. Effectively lowering dynamic cylinder compression.  Which can lower the detonation threshold

And, as already mentioned, MAY,  reqiure little or no change to the igntion timing...

[KV41]

Thanks for the input guys. What I will do is do a dry fit with no piston rings and some clay to get my clearance with the stock gaskets. Then go from there as far as gasket thicknesses go (in my case .060 is the largest ive seen) I know that the stock gasket supposably loses .016 when compressed so I will minus that from the measurement I take. Right? Should I also account for base gasket compression if any?

Ultimately I am trying to get back to around .032 piston to valve clearance. I spoke with a guy who makes copper gaskets today in multiple thicknesses. I have no experience using copper gaskets and the annealing process has me kinda sketched. This bike is for a client and I want no issues down the line. I have ordered another head off ebay just incase

Thanks,

Kyle

[Tracksnblades1]

Thanks for the input guys. What I will do is do a dry fit with no piston rings and some clay to get my clearance with the stock gaskets. Then go from there as far as gasket thicknesses go (in my case .060 is the largest ive seen) I know that the stock gasket supposably loses .016 when compressed so I will minus that from the measurement I take. Right? Should I also account for base gasket compression if any?

Ultimately I am trying to get back to around .032 piston to valve clearance. I spoke with a guy who makes copper gaskets today in multiple thicknesses. I have no experience using copper gaskets and the annealing process has me kinda sketched. This bike is for a client and I want no issues down the line. I have ordered another head off ebay just incase

Thanks,

Kyle

41,

I think 737 was recommending 2) critical measurements.

1) piston to deck height.
  Let's define this here, as the distance from TDC piston to the top of cylinder block (not to the head). This can be a negative or positive measurement. For instance, if your piston measured 0.000 (not -below or +above deck) your ideal head gasket would measure .032 compressed.
 Your piston to head (quench) clearance with a compressed .032 head gasket installed would be .032.

Lets consider a below negative deck piston measurement, for example you measure your TDC piston at .010 below the top of the cylinder. Now your ideal head gasket would measure .022 compressed.    Yielding again your targeted .032 piston to head (quench) clearance after installing a .022 compressed head gasket.

For a Positive deck, your piston measured .005 sticking out above the cylinder block a TDC. Your ideal head gasket would be .037 compressed. We subtract in this case instead of add. 037 - .005 = .032 piston to head  (quench) clearance with a .037 compressed head gasket installed.

This is usually measured similarly on most engines. With a base gasket eventually in the equation, you may be able to split some hairs and achieve your desired clearance.

2) Piston to valve clearance.
This measurement prevents the piston from contacting valves. This condition usually happens during valve overlap as the piston nears TDC, at TDC, or slightly after TDC. Generous clearances here may help prevent contact during valve float. You'll need the minimum recommended clearance here at the very least.

[calj737]

I've yet to see a 550 motor with less than a negative 0.032 piston height. Add the stock gasket of 0.050 and you have tons of room to mill the head and deck (remember, trim those dowels!!). I am pretty confident you'll find you are safe with stock height.

You could always increase the base gasket by 0.010 too, lower the piston into the bore if things are dodgy.

As an FYI, I had a head milled 0.006, and the piston sat 0.032 deep, milled that to 0.000, then used a 0.038 gasket. Compressed, it was 0.032 squish. Piston domes needed to be clearance due to cam profile (a 550/650 does not). You may need to provide a bit of clearance in the head valve pockets. Dry spin your 650 cam in the head and watch the lobe profiles carefully before you dry assemble the motor.

[KV41]

Thanks Guys! I’ve built quite a few motors over the years but most of them have been pretty much in spec. This 550 was pretty messed up from the previous owner and now it’s my problem.


I understand what your saying about piston to deck now after this post and reading about it.

My course of action:

-I am going to measure the piston to deck gap with a deck bridge and dial indicator. Accounting for piston rock.

- Whatever the measurement is positive or negative I will pick the gasket that will give me the .032 clearance.
 (Negative Piston To deck height + compressed gasket = correct clearance (.032)
 (positive piston to deck height - compressed gasket = correct clearance)

Once I achieve the correct piston to deck height. I will then reassemble the head, this time claying the pistons to check for piston to valve clearance ( what is that spec? I haven’t been able to find it).

If the piston to valve clearance can’t be achieved then I could machine the piston for extra clearance or just send the extra head I ordered to be redone haha because it seems like less work.

I’m over thinking the cam timing due to the skimmed head. I believe there’s probably a wide tolerance being that it’s chain driven/ with tensioner and bolted on cam sprocket.

Does this look like the right procedure?

Thanks,

Kyle

[calj737]

Stock pistons and a stock 650 cam won't require piston milling for clearance. Valve pockets, maybe.

You don't have to achieve 0.032 squish; that's an ideal performance tolerance. Stock gaskets were .050 with negative deck height, so probably as much as 0.080 for >90% of the motors in the year.

[KV41]

Update,

So I got the head back from the machine shop and just measured my piston to deck height. It measured at 0.021. ( piston sitting below deck with base gasket (not compressed)

I’ll add the stock head gasket thickness 0.048 - 0.016 (compressed gasket) = 0.032

Giving me a squish total of 0.053.

I believe I’m in spec! right?

Next I will clay my pistons and check for piston to valve clearance.

[calj737]

You'll be fine.

[Tracksnblades1]

Update,

So I got the head back from the machine shop and just measured my piston to deck height. It measured at 0.021. ( piston sitting below deck with base gasket (not compressed)

I’ll add the stock head gasket thickness 0.048 - 0.016 (compressed gasket) = 0.032

Giving me a squish total of 0.053.

I believe I’m in spec! right?

Next I will clay my pistons and check for piston to valve clearance.

👍,

Well Done....

i don't know if the 550 has or if you can find selective base gaskets. Using a thinner base gasket will reduce your your quench a wee bit. If you have access to an online compression ratio calculator, you can input your measurements and quickly compare. Don't be surprised if you only see very minor changes in C/Rs...

[HondaMan]

I'd like to insert a dissenting approach...
In racing, it is/was common to mill off 1mm (0.040") from the head and another 0.5mm (0.020") from the cylinder deck, followed by recessing the valve seats 0.040" and flycutting the piston crowns' valve pockets 0.020" to ensure the pistons and valves would not fraternize too soon. This was done with the 750, 500-4, 350 twins and 450 twins. I think you could do this, too, and simplify this situation?

The head gasket situation: today's head gaskets are all typically 0.010"-0.020" thicker than the OEM ones were. For this reason, you get both a little more space between the valves and pistons, and the need to use rubber seals (O-rings) for the oil jets that are 0.020" thicker to ensure good oil sealing. To find out how much thickness you will need in the end: lay the head gasket onto the cylinders and measure the thickness to the bottom of those oil-passage holes (if yours are still there after previous millings) and then add 0.030" to that height. This is the least thickness you can use to seal those passages: you can also use up to 0.040" more, but if you do, be sure that it is not so tight that it will split the new O-ring seals when the head is torqued down. To test this: use an old head gasket (it will measure about 0.030" thick if OEM) and try torquing in an extra pair of the new O-rings, then remove the head and see if they split or got damaged: if so, go a little bit thinner or bore the recesses slightly deeper into the oil-passage sites to make up the difference. While it sounds complicated, it becomes simple once you try it out.

[Tracksnblades1]

Dissension is productive.....

However, without regards to the OP's intended performance and financial goals,
I'm in total agreement to include machining the block/pistons to achieve ideal quench and valve clearances......actually I like it closer than recommended here....but that's when it's my nickel at risk.....

And recognizing 737 experienced observations with actual factory Honda production deck and head gasket measurements, I agree perhaps Honda didn't place ideal quench as high as a priority as production quotas. And acknowledging they ran well as warrantied.

I'm afraid I'll descent somewhat with your oring recommendations.

While very little has changed in the SAE Low Pressure/Ambient Static O-ring Face Seal compression formulas or machining specifications since the 60's, Modern Oring material selection should be a purposed consideration.  The ever challenging low pressure and ambient static oring face seal relies almost entirely on the correct oring materials, deformation (crush), and surface finish to provide adequate seal life. Since it is not subjected internally or externally (which requires distinctly different machining operations) to pressures that can provide additional oring deformation and sealing.

Temperature, Fluorocarbons, and Orings

Most kit orings of the butyl type have a temperature rating of only 250*f or less.
https://mykin.com/rubber-temperature-range

Current FKM, FFKM, FPM  o- rings are becoming more popular and may perform well within the aircooled engines internal environment.. Additionally SAE and manufacturers have long recommended 70-9O durometer orings as well in Low pressure/ambient pressure Static orings face seal applications.

Sometimes while reading some posts I think we all read something that "Ding Ding Ding" rings the bell, but we read farther and don't respond. Harbor Freight Oring kits...? 50 durometer ? Will split in a standard SAE 30% compression. Plain Nitrile rubber heat rating is 210*...?
https://promo.parker.com/promotionsite/oring-ehandbook/us/ehome/ci.O%E2%80%93Ring-Compression-Force,EN.EN

A link for FKM/FPM offerings from Parker/Haflin include 95 durometer offerings.
https://ph.parker.com/us/en/fluorocarbon-95-durometer-o-ring-v1238-95

Below a link, section 4, covers Static face seal. There is newer technology available but it's only rated for Dynamic face seals right now. 10,000 psig with additional shock and vibration margins, excellent resistance to compression set,  good cold excellent hot temperature performance.
https://www.parker.com/literature/O-Ring%20Division%20Literature/ORD%205700%20Parker_O-Ring_Handbook.pdf

It is sometimes challenging to respond to posts, never initially knowing the aptitude, finances, and goals of those posting. I think those members querying are incrementally diversely informed correctly and encouraged to a self sufficient conclusion.

[Sano]

Wow, that previous o-ring post has my head spinning.  I will make a modest suggestion to simplify the process of getting desired squish and reliable seal at head o-rings.
 1. Measure top of cylinders @ TDC to top of cylinder barrel with base gasket in place and light torque on head bolts. The difference between top piston and top barrel is what gets milled off.
 2. Have your machine shop clean-up/flatten mating surface of head and also remove enough of barrel height to get top of piston height to equal top of barrel height.
 3. Get a MLS(metal laminated steel) head gasket from Cycle X.  This gasket is .040” thick and approx 032”  thick when torqued down.  This gasket solves a few problems, it establishes the squish dimension(032”) and has raised sealing lips around the o-ring holes so rubber o-rings are not necessary, and this gasket can be re-used.  Only down side is both sealing surfaces MUST be machined smooth and flat to seal properly.

On my 550 with DAvid Silver Spares cast pistons (.5mm over) I ended up taking off 042” off the barrels.  No interference with valves using a CB650 cam and a squish dimension (from clay) of 039”.  Hope this helps, I struggled with the same question but came to this approach with help from Calj737

[bwaller]

I don't want to "pile on" because you have a lot of information here. I only want to mention three issues.

1) 0.032" head/piston clearance is bare minimum with stock rods/bolts. Certainly replace stock rod bolts with upgraded 750F3 bolts & nuts will be wise. Very high revs, missed shifts etc. can reduce that clearance, you might be surprised how much. Whether it be piston growth, rod or bolt stretch, but I have seen piston/head contact that had 0.032" clearance. Without Carrillo's aim for 0.040" and it's still far tighter than original. Check this clearance with clay or solder and with gaskets under torque but no need to install the cam.

2) Avoid copper head gaskets for a street engine. They all eventually weep oil which is unappealing! As mentioned an MLS is a better choice. Stock base gaskets are good but original thickness only. Viton coated steel from Cometic are available in 0.010, 0.014, and 0.020" thicknesses. I've always used these and they are "stackable" to give multiple thickness options.

3) Piston/valve clearances should be "MINIMUM" 0.060" exhaust, 0.040" intake. Best way to check....after you have the gaskets selected for piston/head clearance, assemble with the cam and inner valve springs only (or lighter) You'll need to read how to use a "positive piston stop" and a degree wheel properly. Check the intake valve clearance at 10-15 degrees ATDC. Once the crank is in position, "zero" a dial indicator on the retainer, gently pry the valve down until it just touches the piston. (that's why you want a light spring. For the exhaust valves, same deal, only set the crank to 10-12 degrees BTDC. If you choose a stcok cam, just bolt it in, if aftermarket time the cam properly.

Take the time to check all clearances while you mock build. it's also wise to choose Kibblewhite valve springs to replace those 45 year olds!

Good luck

[Tracksnblades1]

Sano,
     My apologies for causing you any type of vertigo. Like I posted above, it's challenging to initially determine the aptitude and true goals of those posting.
     For example lets use your post #14 on September 19, 2019 provided below first attachment. In that post the sentence above P.S., you questioned whether you should split up the required .040 machine cut 50/50 between the top of block and cylinder head to achieve the desired quench/squish. Right now, I ask you, after successfully
establishing your quench/squish, what is your inference as you reread your 50/50 cut question now. Perhaps the same as I thought when I read your query, cutting only half the required amount off the block will only achieve half of the desired quench, right. Or maybe this guy really doesn't understand how to achieve his goal. And may have never rebuilt an engine to this degree, but is reaching out for direction.
    On December 4, 2019 in Reply #4 , attached below, you posted you finally had .024 removed from the block to achieve a .032 squish clearance. Further acknowledging as a result of the block machining, now the oring counterbores would also require machining. You recommend .030 and .040 as the better compression set for the orings.  And on January 21, 2020, reply #3 attached below, you posted you'll be purchasing Honda orings, citing thickness issues with ones included in the gasket kit.

Wow                 so rubber o-rings are not necessary, and this gasket can be re-used.  Only down side is both sealing surfaces MUST be machined smooth and flat to seal properly.

On my 550 with DAvid Silver Spares cast pistons (.5mm over) I ended up taking off 042” off the barrels.  No interference with valves using a CB650 cam and a squish dimension (from clay) of 039”.  Hope this helps, I struggled with the same question but came to this approach with help from Calj737

    However, just today, right above in your #22 reply you posted you removed .042 from the block to arrive at .039 clay squish clearance. In addition you post your using a cyclex head gasket with no orings at all.
    Now, collectively, what am I to believe?  I'm sure one can dig it deeper.

    My head spinning post above was to provide those here with SAE and manufacturers recommendations for oring compression set and modern materials for increased life.  I'm sure Honda used similar available , 40yrs ago.
    While I don't know what you actually have done from your collective posts, I do wonder whether others following your recommended oring set or to eliminate them will enjoy the same success.