Torque plate

[gggGary]

Semi related; my engine guy said 2nd over bores were cake but boring for the 706 pistons in stock liners was tricky, the boring bar produced enough flex in the unsupported lower liner that he had to take thin cuts to end up with a round bore down there. Even with a torque plate, the unsupported section of the liner may be a limiting factor on "roundness".

PS I'm not Gary the "Hooser"

 

[ExtraRegularGuy]

Well I was able to look at the fixture someone uses to hone jugs. What he told me was that the liner has to be a pretty tight fit into he fixture or, like you said gary, it will begin to produce some pretty lame results

 

[TwoManyXS1Bs]

On all my bore jobs, I never took cuts greater than 0.002"-0.003". Deep/hogging cuts could ruin my precision machines and finely honed bits. Could also overstress and damage cylinders. Yes, overbores took a long time, and the customer paid heavily for it.

 

[gggGary]

I was probably dealing with a learning curve of a guy who's business is mainly boring automotive blocks. Free thinking about ERG's comments about a tight fit jig for "honing" Careful before, during, after measurements to confirm this is beneficial. Given that the liner gets "flexy" below the jugs after big bores; Is "super" round a big deal below the ring travel path??? Near all bore, piston skirt wear in that area is fore aft, no matter how round your start it's going to wear oval. Will stay tuned...........As far as stud pressure deformation. The stud nut compression force is located about 3" above the top of the cylinder, distributed by the top cover and head with an iron "helmet" insert.

 

[fredintoon]

He's not questioning anything, Fred: "I guarantee any serious performance build has been torque plate honed." Engines differ on the amount of distortion caused by pressure applied to the head fasteners. Boring with a torque plate is considered best practice on older Harley motors (and that may be the case for newer ones, I don't know.) But these machines aren't Harleys. I'll shut up and let Craig and Gary carry the ball if they want to.

Hi grizld1,
OTOH, check his post #9. It's wording implies he's looking for conformation of what he's learned in school.
(And ain't the new Harleys just like the old Harleys, eh?)

 

[mrtwowheel]

Is "super" round a big deal below the ring travel path??? .

++++++++++++

 

[ExtraRegularGuy]

I'm really eager to get this thing started and get some measurements. If it doesn't distort at all I will be genuinely suprised. I see what you're saying gary, wear is inevitable. At the bottom of my cylinders there is pretty pronounced wear from the pistons rocking around. Correct me if I'm way out in left field, but I want to attribute that to the amount of piston to wall clearence being large because the engine is air cooled. I'm going to do my best to keep these cylinders round and straight, minimize blow by, and have fun doing the whole thing.

 

[ExtraRegularGuy]

Disregard that last thing I said about piston to wall, I glanced at it and read the metric clearence and was thinking in standard units.

 

[TwoManyXS1Bs]

For more entertainment, and controversy, Google this:

"Aircraft cylinder choke taper"

 

[ExtraRegularGuy]

i just read a tid bit about it (one article) and thats wild! Makes me cringe a little bit

 

[Jack]

The cylinder block and head assembly are compressed as a unit held in line by the case studs which have no direct effect on cylinder roundness when torque to the low spec requirements. Shell, Harry,Gary and etc have raced these Xs engine for decades without torque plates. As stated by Griz, liner thickness will effect distortion.
Blow by can be minimized by piston clearance,type of rings and gaps. These XS engines aren't NASA rockets ,they're a low tech engine that produce 45 plus Hp stock. Case expansion is a problem not cylinder roundness.The liner is thicker near the top where the pressures will be at their highest.