Topic: question regarding case boring

[RAZZ]

HI

I'm Collecting parts for a fast street light racer, my plans are going with approx 67 mm pistons / DP298 cam/ Ultra crank /RPE rods/ CCC chains / webers and so, but now I start wondering if..If  I start building the lower engine first and run it with a stock or so cylinder, until I can afford going big, lets say 70 mm pistons and new larger jugs. So my questions is, can I use a bored out case ( for large ccm jugs) with a stock cylinder so i don't have to open up the cases twice and only open / change the top end ?

thanks

Razz

[jonnycakes]

I would think the dowel pins would keep the smaller cylinder centered.

[gschuld]

I would think so.  I have a drag motor that was once a stroker big bore (73mm) motor, then later in life was revived as a 12.5:1 890 using a different cylinder/piston/crank  set using the same cases.

It raced that way for over 10 years like that, so I'd think you would be fine. Sure the locating pins will center the cylinder in the proper location.     

[cbr954]

I did the same thing first built a 836 but knew I would go bigger later so I ground the case out to fit the big bore sleeves.

[RAZZ]

thanks

any advise regarding boring cases ? how to, dues and don´ts - is it easy to do ? and what diameter and clearances should i go for?

[cbr954]

Diameter is going to depend on what sleeves you are going to use, different sizes depending on who made them, I had mine on hand so I side my holes to them.  First time I did it I marked cases with the cylinder I would use and opened up with a die grinder.  Recent set I set up on my mill and opened up the holes.  You will get close to some of the case studs so you gotta make sure you leave enough material.  You can send you cases off to have bored also, I know Cycle X does it.

[T1m32sh1n3]

With a bored case i assume the o rings on the bottom side of stock sleeves dont anwhere to seat

[cbr954]

The orings seal the sleeves to the block not the case, even in stock size cases the orings dont come close to touching the case, the holes arent even round in the stock cases.   The gasket does all sealing.

[T1m32sh1n3]

Gotcha. I new the orings sealed the sleave to the cyinder, i assumed the block helped keep the o ring in place.

[Medyo Bastos]

no chris, like dana said the stock holes arent even round.

[754]

If I were doing them on a mill, , i would  clock the block, then zero the table.. then remoxe block and proceed to bore.
Not sure how much clearance  they should have   bit am thinking 20 thou would do it.
 Boring bar on boring head should do it with studs in place.  ROUND BAR just under the  bearing size, placed in the mill table slots may aid tilting case to desired angle.

[PeWe]

CycleX and Dynoman have the tapered sleeves, claimed to not need case boring for 67mm 890cc, 67.5mmm  (900cc)possible. OD 74mm
 CycleX call this for 915cc wich is not correct, 68mm pistons make 915cc and use thicker sleeves.
My K6 case needed some grinding. My older K2 case had more space and same cylinder with tapered sleeves, 67.5 mm pistons fitted direct.

Dynomans big bore sleeves have OD of 76mm, ID 69mm
Mike's billet block has 77 mm "sleeves". Then add clearance.

Bore the case for eventual future need if going for bigger sleeves. Important to have a good gasket surface on case and cylinder for RCS gasket.

[Bill/BentON Racing]

Definitely check on the tapered sleeves,  I had to grind a little on my K4 cases.

[PeWe]

Make sure to have pistons with enough compression if using long duration cam.

[RAZZ]

Hi did some measuring today, it looks like i need to take some material off about  the holes are 70 / 71 mm. I Think im gonna stay at 67 mm pistons and use tapered sleevs, then i hope i dont  get any trouble closing holes in the alu cylinder walls


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[RAZZ]

PeWe witch pistons  and cam did you use in 900 ccm setup?


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[PeWe]

Wiseco as Cycle X sell as 915cc 67.5mm. Cam DP315. The cam has rather long duration/overlap but smooth power.
Dynoman has 67mm pistons 890cc http://www.dynoman.net/engine/pistons/custom.html#cb750
APE has a crank and rod combo: http://forums.sohc4.net/index.php/topic,168253.0.html

Check with MRieck, if he can gather all stuff, do the job and send it in one shipment. This require a ported head. I'm sure Mike has good cam recommendation since he has built some engines

[Big Jay]

You can not go off of the factory holes. You need a jig that locates on the dowels and has correct bore locations

[PeWe]

I used an RCS base gasket as a template fixed by the 2 dowels, marked with a marker pen when making the case holes larger. I had to do it by a hand machine since I had one case stud I could not remove.  Then test with the cylinder several times to make it fit free and some clearance too.

I had talked to a machinist to mill the cases making it perfect. I made it functional not that beautiful. I tested the block to sit flush with case without base gasket to be sure about clearance to cover for heat cycle. The tapered sleeves need just a little massage, possible with a Dremel or drilling machine. Easier to get it looking better if the diameter of the grinding tool is bigger, not tiny sharp tool drilling way too deep very quick.

[RAZZ]

Thx for input guys.. as  I see it, For minimum i Will need a basegasket or i Can buy your old 900 ccm cyl Per


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[PeWe]

I have ideas to include that in a build.
I have the cylinder w pistons, ported old head w std valve sizes, DOHC 900 rods, k6 transmission, complete F2 and K6 clutches all engine covers, some fun cams... I'll  have to find out how to use the rods if possible since they are 1.5mm longer. If using thicker base gasket, I need to lower the cam holders some....

This is how my K2 build started, I had some leftovers I complete to a  bike I still order parts to I planned to use the 900 or 836/849cc and ported head with Mikuni VM29 Smoothbores to that one, but changed my mind when a friend had a restored shiny K1 stock setup and I have seen really fresh stock bikes here.
Build thread: http://forums.sohc4.net/index.php/topic,168243.0.html