Topic: forged TRW 64mm piston to wall specs?

[paulages]

hey guys- sorry if this should be in the SOHC4 bikes section. mods move if necessary.

i'm running 64mm TRW pistons (811 kit for a cb750) in my 718cc CB550. the engine is apart right now waiting for a head gasket after sealing porosity in the cylinder block. while apart i thought it best to remeasure my piston to wall clearances, and got some strange numbers for such a relatively low-mile engine. granted, i run it really hard.

first off, i can't find the specs that came with the pistons but i believe the desired clearance was .004". my machinist is no longer alive, so i can't ask if he remembers.  

all 4 pistons measure at 2.516" at the widest point on the skirt (on the thrust faces, in line with the pinhole centerline). my measured clearances are:

                                     1                       2                       3                         4
                             top      bottom      top     bottom      top    bottom        top    bottom
                         ------------------------------------------------------------------------
in pin axis:           .0043"   .005"           .0043    .0054"      .0038"  .0038"    .0043"   .0055"

against pin axis:   .0043"    .0049"         .0043    .0054      .0036   .006      .0043     .0056


cylinder #1 is tapered .0007"
cylinder #2 is tapered .0011"
cylinder #3 is tapered .0022", and is out of round .002" at the bottom
cylinder #4 is out of round .0013"

i don't have the world's best bore gauge.. the dial only measures in .0005" accuracy, so gradients in between are estimated. same for the micrometer, though the "zero" on the bore gauge is set off the the micrometer reading for the piston, so to some degree that doesn't matter.

is it possible i could have got distortion from removing and re-installing the liners to have the block sealed? honda lists out of round and taper limits for stock CB350 pistons (64mm cast) at .002". opinions on what i've got here? #3 is the only one beyond those specs, but all seem to have fairly large piston to wall clearances.

[paulages]

i found my TRW spec sheet that came with the pistons.

"AVE. BORE DIA: 2.520"
"MIN. SKIRT CLEARANCE, BOTTOM: .003"

[Big Jay]

I set up a lot of those, and their .003" spec is way too loose. Those pistons were very high silicon like Wiseco and were good at .0015"

Are you measuring 90º from the pin and at the bottom of the skirt?

[paulages]

Are you measuring 90º from the pin and at the bottom of the skirt?

yes. i almost asked you when i ordered the HD studs for this engine earlier... guess i should have. i'll measure AGAIN to be sure, but am pretty disappointed to see this. i have a really hard time believing an engine with less than a couple thousand miles on it has worn this much, making me suspect the boring... especially the taper.

[paulages]

i just measured a set of stock pistons and cylinders that were measured by my machine shop, and i showed .0012" across the board, just as they did. i had hoping inaccuracy in my measuring tools was causing a misreading, but it doesn't seem so.  can anything else go wrong on this engine? wait... don't answer that.

[paulages]

any opinions here, guys? up to .002" taper and .0038 P/W clearances at best, with only 2000 miles or so and no wear marks on the pistons? did my machine shop screw up this bore up, or could the liners being removed/reinstalled cause this?

[754]

I am thinking they set em up loose if you told them you were running it hard.

 Are they 750 sleeves with stock od, then replace em if you want tighter.

 Did they use a boring bar or a honing machine../

[MRieck]

 I would imagine they used a boring bar for the initial boring. They probably finished with a horizontal hone. I would have started with a different cylinder Paul and had it rebored by a different machine shop. APE is close to you. By the time you factor in all your work removing sleeve's, measuring etc, etc it becomes money.
  I agree with Jay about the .003 being real loose. You must have been getting some good blowby. A lot of those old pistons had a boat load of taper built into them and could almost be run at 0 clearance measuring from the bottom of the skirt.

[MRieck]

 I just remembered the size of your block bore ( I was thinking it was a 750 cylinder instead of a 550). I'd start with some new sleeves.

[bwaller]

I hated to be the first to say it Paul, but I agree with the master above!

Since you've done what you can for the block, start again with new sleeves and eliminate more upcoming issues.

Man I hate doing stuff twice, so I think I know how you feel.

[754]

I gotta ask.. if you bored a straight hole, then left .003 for honing.. is ot not a bit hard to get .002 taper..??

 Just saying, in the past some did not use boring bars (though they should).. if they got away with it, they kept doing it..
 I can see where a lot of shops would be leery about reducing clearance.. if it seizes, they get the bad rap..

[MRieck]

I gotta ask.. if you bored a straight hole, then left .003 for honing.. is ot not a bit hard to get .002 taper..??
 Just saying, in the past some did not use boring bars (though they should).. if they got away with it, they kept doing it..
 I can see where a lot of shops would be leery about reducing clearance.. if it seizes, they get the bad rap..

One would think.

[paulages]

they definitely used a boring bar and rigid hone. i've never had problems with this shop before, though to be honest i don't usually go behind them and check their measurements. dan hall is not alive anymore, so it will be hard to back track and figure out what was going on here. in any case, yes these pistons have tons of taper.. i'm measuring 2.511" just below the oil ring, and 2.516". i could see running really tight clearances at the skirt just to still have fairly large clearances at the rings.

however, these sleeves were custom made from cb750 sleeves. it this point, i think it would be cheaper to buy the 64.75mm pistons Soos is offering me and rebore the sleeves. very frustrating no matter what. 64.75mm pistons would make the displacement 736cc though... 

i'm taking the block and pistons to the machine shop this afternoon to verify the measurements.

[paulages]

i took it in to the machine shop and confirmed my measurements.  dan's brother, who does all the boring, wasn't in today though. when he gets in we'll try to figure out why the clearances are so large, but my guess is he'll attribute it to the removal and installation of the liners. in any case, it looks like new pistons are in order.

[754]

 750 sleeves are the cheapest things on this planet.. are you sure you cant use another set bore to proper spec..

 Over the years I have seen head a lot of strange cylinder stories.

 I know 2 guys that own an engine shop X2...had another buddy had a bike only boring bar.. have a buddy that is a well known bikebuilder and an engine machinist..

 I can remember when a shop in town, was boring cylinders with a pulley and weight with drill driven hone..

 I for years have heard horizontal  Sunnens and Ammcos referred to as "F*CKER HONES".. and all the stories that went with them..including a 2 stoke barrel grabbbing & spinning and taking a finger with it.... and how much they would actually remove on them, ie big-bore..

 I have refaced the bottom side of the part of a Van Normam boring bar (clamp-on), that was maybe .. like .006 or .008 out of square in a foot..

 I have built fixtures to  square up gasket surfaces on Hog barrels.. and ones to hold cylinders in CK 10s.. and a whole whack of torque-plates for various things.. including cutting out  nearly 1/2 out of  soon to be 1200 Sporty barrels, leaving a few thou to hone.. and I have seen/heard some crazy sh!t..

 so what I am trying to say.. sometimes it aint done on the machine you think it is.. and just cause someone always had good results ( or highly experienced), does not mean the odd bad day  does not occur.. FWIW..

[paulages]

750 sleeves are the cheapest things on this planet.. are you sure you cant use another set bore to proper spec..

sure they are. want to machine them down to fit my 650 cylinders for that cheap? 

[kos]

A hone has one purpose...to leave your bore with the proper finish for good ring seal. Any one can try hone it to the next OEM bore size,  but the bore is usually not round when done. This method is for hurry up we, are at the races, we got to make the main event type thing...  When doing customers or your own work, take it to a shop with a boring bar. And, if your lucky... the specialize in  your type of bike and they might even have a deck plate to really make it perfect.

KOS

[paulages]

this was definitely done on a dedicated boring mill and honed properly by a guy that's been doing the same thing every day for 40+ years. like i said, i can't verify that the clearances were proper the first time around, but i've watched him work before using the bore gauge during the final honing. i'd be really surprised if there was more than .0005" taper when it went out the first time. i have to assume that the liners warped when i removed and re-installed them, i just don't understand why, nor why there is taper in particular. in any case, unless i can prove that impossible and that it was done wrong the first time around, i really doubt they're going to take the blame.

[754]

 I hope you meant boring bar, not mill.. a boring mill is well.. a lot bigger..

 So I have to ask .. were your sleeves pressed in place, and not removed since.. in your cylinder.. Before the final honing was done..??
 and was there any mods done to the OD of said sleeves before installing in cylinders?

[nokrome]

I hope you meant boring bar, not mill.. a boring mill is well.. a lot bigger..

 So I have to ask .. were your sleeves pressed in place, and not removed since.. in your cylinder.. Before the final honing was done..??
 and was there any mods done to the OD of said sleeves before installing in cylinders?

i thought a boring bar was a tool used on a lathe or mill to bore a hole
  do you mean boring machine ?

[754]

 It could be called a boring machine, but a boring mill is different.
 Some of the automotive boring bars, are a rotatating feeding boring bar with a heavy base plate. This can be set on a plate for certain jobs, but on a V8 block the  bank is first set up level. Then the boring bar is lifter into place, centered, and clamped down.
 
 Boring in a lathe, the boring bar is stationary (most cases), and work is spinning. In a milling machine work is stationary, and bar is spinning. In a horizontal boring mill, work is stationary, bar is spinning. A vertical boring mill has work spinning and bar stationary.

 In a dedicated Bike cylinder boring bar (common types) the  cylinder is monted on a table, the rotating boring bar is underneath.
 There is other ways of doing it as well, ie radial drill press with boring head. or in a lathe, ie cylinder statinary , and bar spinning..

 I am curious what they actually used and what was done to the outside of the sleeves..

[paulages]

It could be called a boring machine, but a boring mill is different.
 Some of the automotive boring bars, are a rotatating feeding boring bar with a heavy base plate. This can be set on a plate for certain jobs, but on a V8 block the  bank is first set up level. Then the boring bar is lifter into place, centered, and clamped down.
 
 Boring in a lathe, the boring bar is stationary (most cases), and work is spinning. In a milling machine work is stationary, and bar is spinning. In a horizontal boring mill, work is stationary, bar is spinning. A vertical boring mill has work spinning and bar stationary.

 In a dedicated Bike cylinder boring bar (common types) the  cylinder is monted on a table, the rotating boring bar is underneath.
 There is other ways of doing it as well, ie radial drill press with boring head. or in a lathe, ie cylinder statinary , and bar spinning..

 I am curious what they actually used and what was done to the outside of the sleeves..

ok, i'm not a machinist so i apologize if i'm referring to the machine wrong. i'll find out exactly what it is next time i'm in. there is a table the block is bolted to, and the boring bar (or whatever) works from above. before dan died, he showed me several small bore motorcycle boring bars he has in the back. he said they became obsolete when he bought the machine that is in use now.

frank- maybe i should explain the background a little better. some here remember the project when i built it (think it was before you were on the forum), and others may have read the article i wrote about it. anyway, the bottom end of the engine is a 550, but the block is from a 650. the cylinders were bored out to fit 750 sleeves, which were shortened and tapered to fit the 650 block. then, they were bored out to 64mm. THEN, the goddamn thing leaked oil like a sieve until i figured out that the problem was that i had hit porous casting when boring out the block to fit the over sized sleeves. i dropped the sleeves out, sent the block out to get sealed, and re-installed the liners.

...which brings me back to my original question. was it the removing and re-installation of the sleeves that caused the taper in the holes? i worried about this when i pulled the liners, but i didn't really have any choice.

[nokrome]

hi paul,
  sorry to hear to hear about this, seems like one thing after another
    what is the process to get the sleeves in and out of the cylinder?

[paulages]

hi paul,
  sorry to hear to hear about this, seems like one thing after another
    what is the process to get the sleeves in and out of the cylinder?

heat to 300F and they pretty much fall out/drop in.

[paulages]

here you go guys. the machine is a Sunnen Cylinder King.




the man that does the work says he is certain it went out the door right the first time, and i believe him. at this point, i'm resigned to using larger pistons. oh well, maybe it'll be good for another few ponies.

i'm wondering if i took material off of the bottom of the sleeve bore when bead blasting prior to the sealing process. i did focus attention on the bottom half of the holes, as that is where the leak seemed to be happening and where oil staining was worst, but i use a very mild abrasive in my blasting cabinet.