One for the 250cc folk

[fordboy628]

An alternative is to contact Carillo here in the US and to describe your problem.  They can build you a set of rods for available big end shells.  Then, the crank journals need to be resized to fit the shells.  It is expensive, but it is a way to go if nothing else works.   

Yes it is.   And perhaps the only way forward at some point in time.

I find myself doing it more and more these days as bearing stocks become depleted for "older" (read that unprofitable) product lines.    And then there is the issue of a "race quality" bearing, an even rarer duck for "older" product lines.

"Why are you beating your head against the concrete wall daddy?"      "Because it feels so good when I stop . . . . . ."

 

 
Fordboy

[generatorshovel]

I went down the Carrillo road with the 175 single Bo, that bike may get finished when I repair the 250.
Fordboy, since stripping the crankcases and checking oil galleries for reasons the main bearing shell failed (no damage to the journal), I found none, clean as a babies bottom.
When setting up the piston oilers I fitted an aux. oil pump, just to feed the squirters, but after testing I decided that the aux pump would not be needed,,,I guess that decision was wrong.

Pressure dropped from 70 psi, to 50 psi when the squirters were activated( something else I forgot to do during the run), the pistons survived without oil cooling.
I have found most of the bearing shells I need, with exception of one rod set for the replacement rod (the damaged cylinder's rod now has some slight twists in it).
The head took the brunt of the force, sparing the crankshaft from visible damage.
This bike has the same financial limits all of my projects have, keeping fun as the 1st priority, and doing the best I can, given the realistic goals I have.
Throwing cubic dollars into the engine might lift the bar, but until I sort the setup I have, or some fool wants to waste some sponsorship dollars on it, I'll use the KISS method.
A boost increase to 20 psi might not hurt (much) after all, Dave Plecas has boosted his stock bottom ended CT110 to 45 psi, without failure,,yet (111 mph in 2014)
Tiny

[fordboy628]

Tiny,

It is usually how a crank is drilled that dictates the pressure required in use.    It is possible that this setup requires 70 psi (or higher) for adequate oil flow to prevent contact/damage.

Since the general rule of thumb is 10 psi per 1000 rpm, it seems to me to be a "lower" oil pressure system, with 70 psi at the bottom of the reliable range.

Honda did lots of work in the 60's & 70's in an effort to gain power output by reducing "parasite drag" and parasitic power losses.    It does work, but it cuts the margin to component failure to the absolute minimum.

Problems can arise when you don't know the minimums . . . . . .    And, as you are aware, destructive testing can be expensive.    Although there is no arguing about the finality of the results.

 
Fordboy

[wobblywalrus]

The Carillo rods can be ordered as "top loaders" so the big end shells can be checked or changed from the cylinder side of the motor.

[generatorshovel]

Bo, these engines have the barrels as part of the upper crankcase half, pistons & rods have to go in from the top, no access to "upside down" bolt access 

I'm finally ready to re-assemble the engine, when the weather  warms a bit, using the only bigend shells available, Chinese    , actually, they are well made, and within standard specs, with +.25 mm available, but these would require a crank re-grind.

Main bearing shells were available from Honda, once I got over the "do not sell outside of Japan" hurdle , as it turns out, the later model MC22 engines shared the same main journal size, but with more sizes available (in .006 mm graduations)

I have been talked into entering the Boca Bearing comp again, and would appreciate a vote or 2 if anyone hase the inclination to do so (votes need to be verified via email 1st, but you won't get spammed by doing so)
http://www.bocabearings.com/innovation-contest/ContestantDetails.aspx?ProjectID=197

July voting is almost finished, but votes can be done  monthly ( I might get a free tee)
Tiny

[generatorshovel]

Here's another thought provoking post , Fordboy, as usual will have good advice,,
I'm in the process of rebuilding, with another head (pentroof 4 valve) which, after having .4mm skimmed off to flatten it, results in contact 'tween head/piston
I have yet to figure the best way of measuring the clearance I had, with the last head, but that too had been skimmed, and I feel it was so close to having a similar piston/head collision, although I have not found any evidence this happened.
These engines have a 33.8 mm stroke, 49.5 mm bore X 4
According to this
http://www.mssholdings.co.uk/documents/1812_1368456939_Performance-Bikes-Article.pdf
The CBR250/4's suffer
12,000 rpm .013" 'rod stretch
16,500     .023"   "     "
18,000     .0235"  "     "
So, by adding .0235"(stretch @ 18,000rpm) to .02362"(desired minimum clearance) = 0.0706"

(0.00119 mm) I will know how thick my head gasket needs to be.
The fun bit is to measure the clearance I have (less than ZER0), and had (the last head was .4mm

fatter(.0157")
Tiny

[fordboy628]

Here's another thought provoking post , Fordboy, as usual will have good advice,,
I'm in the process of rebuilding, with another head (pentroof 4 valve) which, after having .4mm skimmed off to flatten it, results in contact 'tween head/piston
I have yet to figure the best way of measuring the clearance I had, with the last head, but that too had been skimmed, and I feel it was so close to having a similar piston/head collision, although I have not found any evidence this happened.
These engines have a 33.8 mm stroke, 49.5 mm bore X 4
According to this
http://www.mssholdings.co.uk/documents/1812_1368456939_Performance-Bikes-Article.pdf
The CBR250/4's suffer
12,000 rpm .013" 'rod stretch
16,500     .023"   "     "
18,000     .0235"  "     "
So, by adding .0235"(stretch @ 18,000rpm) to .02362"(desired minimum clearance) = 0.0706"

(0.00119 mm) I will know how thick my head gasket needs to be.
The fun bit is to measure the clearance I have (less than ZER0), and had (the last head was .4mm

fatter(.0157")
Tiny

Tiny,

Where is the contact located?    On the flats?   Or is there contact in the "pent roof" area?

How did you get a .0706" total from .0235" + .02362" ?    I get .04712".   Is there something left out of the math?


When confronted with this situation, I usually find "zero" by using feeler gauges/head gaskets to raise the head on the block.   The tricky bit is to find "zero".

It never hurts to err on the "plus" side by a small amount.

How much piston "rockover" at TDC overlap do you anticipate?   I'd measure the rockover in a cold bore just to get a number.   You might be surprised at how much there is and you might want to increase your piston to head minimum clearance.   Check it to be sure.

 
Fordboy

[generatorshovel]

Fordboy. thanks for your help (again) Contact is just in the areas shown in the pic , (on all 4  cyl's)
Math was not one of my favorites at school .

Rockover has not been measured, only "looked at" and is considerable, but won't be a problem as the collision area is parallel to the pins,
In hindsight (laying in bed thinking last night) after removing the head face, the tapered area in the combustion chamber (where the collisions occur) has changed shape(shortened due to taper), I should also check the squish clearance with the "old" head too,
I'm thinking, the engine was fine with a 1.6 mm head gasket before .4 mm was shaved off the bottom on the "new" head, this would work, so if I get a new gasket made @ 2mm, things "should be" ok , but thinking is not proving I guess ?

Edit >>>>

This pic shows the contact areas on the pistons

Tiny

[generatorshovel]

I didn't get the time to Adobie & upload the piston contact pic before going to work this morning, the above pics will help explain where the contact is made (all 4 cylinders)
Tiny

[wobblywalrus]

Cometic here in the US is good at making copper gaskets for custom applications.  They might be a help if none can be made in AUS.

[bones]

Hey Tiny
   You say you skimmed  0.4mm off the head to make it flat
  Did you need to remove the full amount to Just clean it up?
  Are the cam tunnels now bent but you have a flat head surface?

  Maybe try to fit the head and the cams to see if they spin ok

 cheers   Bones

[generatorshovel]

Cometic here in the US is good at making copper gaskets for custom applications.  They might be a help if none can be made in AUS.

Bo, I'll use the "almost local" firm who made the last one, I was more than happy with it, thanks anyway .

[generatorshovel]

Hey Tiny
   You say you skimmed  0.4mm off the head to make it flat
  Did you need to remove the full amount to Just clean it up?
  Are the cam tunnels now bent but you have a flat head surface?

  Maybe try to fit the head and the cams to see if they spin ok

 cheers   Bones

Bones, it was ok crossways, from 1 to 4, but needed the .4 mm removed to flatten the area of the gear drive area that "pokes out"
Most 250/4 heads need a skim for the same reason.
I worked out the piston(s) just touched in the areas marked in the previous post pic, which meant, seeing this head is skinnier than the previous by .3mm (not .4 as 1st measured roughly) and once checked (checked, not relying on my memory this time) meant even when I raced this year, I didn't have enough clearance, although no piston/valve contact was evident (except for #3 , which ate a valve & valve seat)
She'll be apples with a 1.6mm gasket .
I had another problem too, cam drive gears tend not to enjoy being forced together as a result of the head skim (not adjustable)

[fordboy628]

Fordboy. thanks for your help (again) Contact is just in the areas shown in the pic , (on all 4  cyl's)
Math was not one of my favorites at school .

Rockover has not been measured, only "looked at" and is considerable, but won't be a problem as the collision area is parallel to the pins,
In hindsight (laying in bed thinking last night) after removing the head face, the tapered area in the combustion chamber (where the collisions occur) has changed shape(shortened due to taper), I should also check the squish clearance with the "old" head too,
I'm thinking, the engine was fine with a 1.6 mm head gasket before .4 mm was shaved off the bottom on the "new" head, this would work, so if I get a new gasket made @ 2mm, things "should be" ok , but thinking is not proving I guess ?

Edit >>>>

This pic shows the contact areas on the pistons

Tiny

Tiny,

There are 4 choices for fixing your "interference" problem.    I'll add some thoughts/comments:

1)   Hand fettle the piston domes.      NOT RECOMMENDED, too subject to variations.

2)   Machine the piston domes in/with a fixture.      ALSO NOT RECOMMENDED. Honda bike pistons I've seen all have "hollow" domes, you don't want to get too thin in cross section.

3)   Hand fettle the interference points in the chambers.    Acceptable, but a lot of checking and cc'ing to "equalize".

4)   Machine the interference points in the chambers with a fixture.    BEST, and most accurate.   Also, biggest PITA*.   Still need to check and cc, etc.

Regardless of which solution you choose, seems like the head becomes a slight "one off" unit, pretty common with hand built race engines.

Pick your poison . . . . .
 
Fordboy

[generatorshovel]

Option 5 is my choice,
 A 2 mm head gasket will give me .0354" clearance (same as with head #1) which is more than enough to allow for rod stretch / crank flex past the operating rpm
I may have to remove some alloy beneath the 3rd cam gear and shim the cassette to suit , this is also a PITTA as the gear is a "scissor" split type , spring loaded,(to quieten the gear train), this makes measuring the gear fit difficult, but if I spread the "scissor" gear to line up the teeth, clamp it, then measure the lash I should be ok ?