normal tolerences

[orderofsion]

hi guys , ive got an old '86 k5 . can anyone out there help me with this one. having read the excellent rebuild guide i was inspired to check out my squish and compresion . i've never previously done this to this or any other engine . first i tried the 2mm solder and at TDC no pinch ! so with the exhaust off i placed a pea sized lump of warm wax onto the top of the piston just by the port and and turned the engine through TDC . when i took it out i got a squish reading of 4mm !
 when i took the head off i discovered that there were 2 thick head gaskets fitted and as best as i can tell they are 1.25mm each , they look factory made also the (new wiseco) piston stops about 0.8mm short of the top of the cylinder , at BDC the bottom of the exhaust port is 2mm higher than the top of the piston and the bottom of the inlet transfers are 1mm lower than the piston . the top of the exhaust port is level with the top of the kips but if the duration is measured around the BDC cycle then it is about 190' . is any of this normal ? my budget is tight , where do i start ? please help.

[mun]

Your values are ok for stock bike!

There are my old std values:
http://img88.imageshack.us/img88/6012/1986kx500b2tiedoteng26lv.jpg

[doordie]

Mun,your are nice to cheer your data to him!
But 4 mm in squish is far to much don?t you think Mun?
I will suggest to take away one of these headgasket.
What is thickness of basegasket?
I think someone have raised the barrel to get higher porttimes and
even raised head  with 2 gaskets and that because of low oktan of gas.
You can measure volume of head and see what numbers you get
orderofsion.

//doordie

[mun]

Sorry Doordie. I must always correct my writing and always you are right.

If "orderofsion" take second head gasket off, so squish height is something like me std and it is badly too big. Best value to squish height is about 1,6-1,3mm and as Doordie says, not below 1,3mm (http://www.kxriders.com/forums/index.php/topic,1406.0.html).

I have newer buy original base gasket, so don't know its thickness. I have make base gaskets of different thickness paper, mostly 0,6mm. Your 0,8mm piston top to cylinder top is little big, so there can be base gasket about 0,8mm? Sometimes thicker base gasket is better. You get more degrees to exhaust, but some more degrees to transfers than exhaust > little easier to ride.
Then you must change head gasket too for squish height. You can make own head gasket of different thickness copper. Copper gasket works fine if you soften it sometime with torch.
Some tuners raise cylinder quite lot so that get degrees what he want. Then he shaving top of cylinder to get squish height back to correct.

Don't bother bottom of ports. You get not more power even you lower them to BDC, especially exhaust port.

[orderofsion]

Thanks for all your help guys . Looks like I've got some measuring to do but hopefully I'll soon be out of this 40hp hole my bike is stuck in . One more question though , from Muns data I wondered if all k5 pistons have a flat top like mine ?
  Thanks.

[mun]

Orderofsion:
I have flat top piston too and i guess that all kx500 have it.

Something what you could to do with your cylinder:
Raise exhaust to about 195deg, side exhaust 2-3deg more. Don't make exhaust duct bigger, only port. Maybe last 2mm raise quite steep, only about 10mm to duct. This help keeping gas in speed.
Raise main and second tranfers so that when main exhaust open to main transfers open is about 32 degrees. (32 is very very old fine starting point.) Less degrees (higher transfers) mean more rideable motor and more deg. more hit power (more dyno power.  ) This depend very much of your pipe and your personal will. Raise boost transfer about 1mm less than main and second.

You have 2 choice:
1. Raise all ports, or
2. raise cylinder to get boost transfer or port which need less raising ok degrees. Make spacing plate of aluminium or so and use paper gasket both side. Remember that paper goes thinner in use. Raise all other ports.

If you select 2, then you have 2 choice:
1. Shave top of cyl. same mm what you raised cyl, or more to get squish in order.
2. Cut gasket level of cylinder head so you get squish in order. You cut nothing center of head, only gasket level. Then squish and whole combustion camber can drop to cylinder. I know that some of WC RR125/250cc-team use this. It's nice when your motor knocking, so your's cylinder top not ruined.

Then you must make combustion chamber back to bigger. How much depend of fuel.

I try to put Excel-attach (size 29kt) to this message. I change xls-extension to txt. Change it back to KX500std-86 eng.xls. With those Excel you can plan degrees and compression ratio.

Doordie: Would you check my writing again? 

[mun]

I save KX500std-86 eng.txt to MuN-gallery. You get it from there.

[orderofsion]

Thanks again for the help. I've done some careful measuring and come up with the following figures .Some measurements were easy to do and have a high degree of accuracy , others were trickier and may be subject to +or- 0.2mm.
 main exhaust port= max height 39mm , height from bdc 41mm
                            effective width (measured as a straight line across port)50.5mm , ex port duration = open for 195'
 kips ports = 1/2mm lower than main port , height 15.5mm , effective width 16.9mm.
 transfer ports between 69 and 70mm from top of cylinder.
with both head gaskets removed and surfaces cleaned up squish=1.6mm ! judging from this data I would guess that my exhaust and kips have been tuned and my cylinder head de-tuned . Some how I have forgotten to measure the width of the transfers but I get the feeling they may be standard. I've just got a 50ml syringe so I'll check the chamber volume on monday . To get the squish right I'm going to have to bore out the cylinder head a little as the origional 86mm bore is too small for my 87.5 piston. Oh I cant wait for the first test ride !

[mun]

Looks like someone have already raised exhaust port, if it's so high, 195'.

Don't bother too much width of ports.
Main exhaust port max safety width is about 70% of bore.
Don't make changes to front of main transfer port. Space between transfer ports can be narrow, but it's not very important to do first.

Do you get open KX500std-86 eng.xls?

[doordie]

Mun, have you taking english lessons?
I?m spelling like crap,and you have take it to a
another level.

Listen to Mun how to do a good porting on a 86-88 barrell.

//doordie