Whats a dot??

[harryhoarder]

Bit of a newbie question but what is a dot head??  And why are people fitting them?   I assume is a head from a later model bike. 

[CockneyRick]

Side of the head has a dot/blank mark on it. Not my area but i believe ports/cams are the sought after point!

[fatblokeonbandit]

GSXR750 J/K cylinder head and cams, used to be an extremely cheap way to make a b12 engine much more lively,  Ive done 3 over the years and you can literally bolt it all on ( after sorting fuel tap carb issue.)  and get 25 or 30 hp more after sorting carbs, also you used to be able to get a complete engine for £100 or so, those day long gone, I got one many years ago with completely shot gearbox and out put bearings for £30..

Also the head is fitted to teapot 750s but with much softer cams, 

[harryhoarder]

Thanks for that!!  A bit more knowledge to add to the little I have. 

[Lachie04]

On 3/4/2018 at 2:15 AM, fatblokeonbandit said:

GSXR750 J/K cylinder head and cams, .......................... you can literally bolt it all on

 

Obviously been done a few times here and thinking of doing it on another motor build but..

Question I've been meaning to ask would you not have to machine out the squish band to match the new cylinder diameter?

I would think the sharp edge would create a hot spot in the chamber

 

[Fazz711]

Short stroke j and k 750s have same bore size as 1100 gsxr 

[clivegto]

1 hour ago, Lachie04 said:

 

Obviously been done a few times here and thinking of doing it on another motor build but..

Question I've been meaning to ask would you not have to machine out the squish band to match the new cylinder diameter?

I would think the sharp edge would create a hot spot in the chamber

 

No.

[fatblokeonbandit]

What's a squish band

[vizman]

3 minutes ago, fatblokeonbandit said:

What's a squish band

....It's a bit like your waistband shippers

[fatblokeonbandit]

13 minutes ago, vizman said:

....It's a bit like your waistband shippers

What slim and muscular

I must see if my cummerbund still fits,  

[dupersunc]

3 hours ago, Lachie04 said:

 

Obviously been done a few times here and thinking of doing it on another motor build but..

Question I've been meaning to ask would you not have to machine out the squish band to match the new cylinder diameter?

I would think the sharp edge would create a hot spot in the chamber

 

The squish isn't any different to an 1100 head, the chamber is shallower though which raises the compression ratio. 

The edge of the squish band is the only place in a combustion chamber you want a sharp edge, the turbulence it creates mixes the air fuel better and reduces the size of the fuel droplets, this creates a faster burn reducing the likely hood of detonation.

2 hours ago, Fazz711 said:

Short stroke j and k 750s have same bore size as 1100 gsxr 

Sure about that?

[Lachie04]

1 hour ago, dupersunc said:

The squish isn't any different to an 1100 head, the chamber is shallower though which raises the compression ratio. 

The edge of the squish band is the only place in a combustion chamber you want a sharp edge, the turbulence it creates mixes the air fuel better and reduces the size of the fuel droplets, this creates a faster burn reducing the likely hood of detonation.

Sure about that?

Voted best answer 

[Fazz711]

14 hours ago, dupersunc said:

The squish isn't any different to an 1100 head, the chamber is shallower though which raises the compression ratio. 

The edge of the squish band is the only place in a combustion chamber you want a sharp edge, the turbulence it creates mixes the air fuel better and reduces the size of the fuel droplets, this creates a faster burn reducing the likely hood of detonation.

Sure about that?

You are correct i was wrong. I always assumed that the head off the short stroke j fitted because they were the same but I am wrong. Gsxr750j bore is 73mm stroke44. 7mm gsxr1100g 1052 motor is 76mm bore stroke is 58mm gsxr110k is bore78 stroke 59mm. My bad for assumptions the mother of all f##k ups. 

[canamant]

16 hours ago, Fazz711 said:

Short stroke j and k 750s have same bore size as 1100 gsxr 

short stroke 750s (748) have a 73mm bore while 1052 has 76mm bore and 1127 has 78mm bore

 

[VJ]

On the subject of dot heads, anyone know what compression ratio a 1127 with a DOT head would have? I'm building one and Ive been trying to work it out for ages but I need measurements of volumes that I can only get by taking the engine back apart.

[Lachie04]

40 minutes ago, VJ said:

On the subject of dot heads, anyone know what compression ratio a 1127 with a DOT head would have? I'm building one and Ive been trying to work it out for ages but I need measurements of volumes that I can only get by taking the engine back apart.

Recently did a rebuild and my guy cc'd the head  the DOT head volume was 22.5 ml and the 73mm 750 piston crown was @4.31 ml (probably within a whisker of a 1127 piston would suspect) at least give you a ball park to look at

There is a few sites that have calculators for CR some are different and come out with all sorts of different values but this one looks reasonable unless you want to work it all out yourself

http://www.csgnetwork.com/compcalc.html

Edited March 14, 2018 by Lachie04

[Nik]

2 minutes ago, Lachie04 said:

Recently did a rebuild and my guy cc'd the head  the DOT head volume was 22.5 ml and the 750 piston crown was @4.31 ml (probably within a whisker of a 1127 piston would suspect) at least give you a ball park to look at

There is a few sites that have calculators for CR some are different and come out with all sorts of different values but this one looks reasonable unless you want to work it all out yourself

http://www.csgnetwork.com/compcalc.html

Great info!

[VJ]

On 3/14/2018 at 6:34 PM, Lachie04 said:

Recently did a rebuild and my guy cc'd the head  the DOT head volume was 22.5 ml and the 73mm 750 piston crown was @4.31 ml (probably within a whisker of a 1127 piston would suspect) at least give you a ball park to look at

There is a few sites that have calculators for CR some are different and come out with all sorts of different values but this one looks reasonable unless you want to work it all out yourself

http://www.csgnetwork.com/compcalc.html

Cheers chap, i must be having a brain fart moment though because I still cant get sensible numbers in the output, I keep getting 28cc total displacement etc which even x4 is obviously not right for an 1127cc motor lol

 

Cheers

John

Edited March 18, 2018 by VJ

[Lachie04]

9 hours ago, VJ said:

Cheers chap, i must be having a brain fart moment though because I still cant get sensible numbers in the output, I keep getting 28cc total displacement etc which even x4 is obviously not right for an 1127cc motor lol

 

Cheers

John

I think the volume calculation is not the same as displacement have done it a couple of times on different calculators and  still comes out to 13.3 (OR .4):1.

Wouldn't worry about the other I think it is a swept volume

 

 

Or              (281.7 + 22.5) / 22.5 = 13.5:1 (rough)

To be honest if I do it for a dot head and barrel it comes out to 9.9 or something and I was pretty sure they are supposed to be 10.9:1

Edited March 19, 2018 by Lachie04

[Gixer1460]

That second calc looks right but suspect the 4.5 should be -4.5 (yes I know what it says - its a hunch!) Just try it and see? 

[Oilyspanner]

I had to allow for the head gasket thickness too, which on mine was .8mm when torqued down - easiest to measure old one.  I wish I'd used a burette to measure the chamber volume, it's the most accurate.... even better - could've given the engine to Ray Debben, he's only down the road !  nah, working on these bikes is good fun and besides my spanners wouldn't be oily !

[Sandman]

According my measurements, the piston deck clearance is approximately 0.25 mm with cylinder gasket (compressed). Thickness of cylinder head gasket is 0.76 mm.

Thickness of cylinder head gasket + piston deck clearance=1.0mm -> volume is 4 .85 ccm.

The cylinder volume is 1127/4=281.9 ccm. The effective dome volume is 22 ccm (approximately).

CR=(281.9+22+4 .85)/(22+4 .85)=11.5

The compression ratio is 11.5:1 by using a DOT head on a 1127 ccm GSXR 1100.

Standard compression ratio for a 1127 ccm GSXR 1100 With 26 ccm effective dome volume is

CR=(281.9+26+4 .85)/(26+4 .85)=10.0

 

 

[VJ]

this is why this forum is the font of all knowledge, cheers guys 

[Sandman]

According mye measurements, the actual dome volume of the cylinder head is 27 ccm for a GSXR 1127. The piston dome volum for standard pistons  appr. 1.0 -1.1 ccm.  Effective dome volume is 25.9 ccm -26 ccm.  The deck heigth,  piston to valve  clearance ,and piston to head clearance must be carefully measured when using highlift cams and high-comp pistons. I run CR 13.6:1 and webcams 236/223  and race ported head (GSXR 1100 engine and GSXR 750 RR -88 frame).