Measuring squish band and deck height

[Guest]

Hey guys,

I've finally got the lower end of my 550/650 build together and now comes the fun part. I have a few questions for the experts. Sorry for so many as this is my first time going to this level.

I want to get the squish band right so I was wondering if I can put the cylinder on without the gasket or is it necessary to waste one for measuring?

If I can go gasketless, how do I determine the torqued thickness of the gasket?

If I put solder on the piston and measure the compressed thickness at the ends, that is telling me the squish measurement correct? How does that relate to deck height?

Lastly, do I need to measure each piston or can I get away with just putting one piston on and just measuring the one?

BTW, I'm using an OEM base gasket that measures .54mm thick and the head gasket measures 1.4mm.

Thanks,

Sci85

 

[boontonmike]

Don't over think it. Put in stock gaskets and run it.

 

[GregT]

Don't over think it. Put in stock gaskets and run it.

Well, yes, you could...but you've gone this far now...

You should be able to put a fresh base gasket in, do a trial assembly of the block and pistons - pistons without rings,pins just pushed in etc. Measure piston crown to deck distance - but don't forget to put spacers on at least 6 studs and nip the barrel down when you measure.
Piston crown edge to top of deck plus gasket thickness equals squish height.
Ideally you're aiming for around .040in or 1.0mm for road and general use.
Anything which needs to come off to achieve this comes off the top of the cylinder block.
If you're careful, the base gasket will be OK to use on the final build.

 

[Suzuki_Don]

There are different ways of checking the squish band distance. The way I did it is covered in my build thread. You can also adjust the squish band distance by using different thickness base gaskets which is what I did.

On my motor the upper piston land was .022" above the metal liner in the cylinders. The head gasket was .050". The maths is 50 - 22 = 28. So the squish band clearance in my case was .028". To get it up to around .040" I needed the raise the cylinder head away from the pistons to provide more clearance. A thicker base gasket was my solution. There is a thread on how I made that base gasket if interested.



.

 

[Guest]

Yeah I've been reading your procedure Don and plan to do the same. My questions were more related to the use of gaskets and assemblage of the pistons for measuring purposes only. I just don't have a spare base gasket (I did manage to salvage the head gasket). So I seemed to recall seeing someone say they measure deck height without the base gasket. I was hoping someone had a process for that. I do have an unused 550 gasket that I could probably use but it's slightly thinner than the oem 650 base gasket. I might go that route if measuring without the gasket is not possible.

 

[Suzuki_Don]

Yeah I've been reading your procedure Don and plan to do the same. My questions were more related to the use of gaskets and assemblage of the pistons for measuring purposes only. I just don't have a spare base gasket (I did manage to salvage the head gasket). So I seemed to recall seeing someone say they measure deck height without the base gasket. I was hoping someone had a process for that. I do have an unused 550 gasket that I could probably use but it's slightly thinner than the oem 650 base gasket. I might go that route if measuring without the gasket is not possible.

Clay it is fine to use a new base gasket and head gasket when doing trial fittings even if they are torqued to specs. As long as they have not done any heat cycles then they will be fine to reuse. When you release the torque on the head gasket it will expand back to close to it's original thickness when new. Put the base gasket on dry for these fittings and give it a thin coat of grease on both sides when fitting it for the final time.

 

[Guest]

Ok cool. I did not know you could reuse the gasket. What's the grease coating for? I was always under the impression gaskets and their surfaces needed to be clean and grease free.

 

[Suzuki_Don]

Ok cool. I did not know you could reuse the gasket. What's the grease coating for? I was always under the impression gaskets and their surfaces needed to be clean and grease free.

The grease has two benefits. The first is that it helps make a good seal and the second is that it makes the gasket easier to remove in the future. Just general purpose axle grease is fine.

 

[Guest]

Sweet! Ok, I'll put it together tomorrow and get the initial measurements. Thanks Don.

 

[blowerbike]

i check deck height without a base gasket/rings or clips.
measure over the wrist pin center lines with calipers and get an average.
do the math.
zero is great but a few in the hole is better than the piston sticking out into the head gasket.
rods do stretch at high revs so be aware.

and yes i use old wrist pins on half of the studs snugged down.

 

[rapidray]

I do it EXACTLY the same way as Terry just stated. Ray.

 

[Guest]

So when you guys Do this without the base gasket in place, how do you figure that part into your calculations?

 

[rapidray]

You add in the base gasket thickness. Ray.

 

[blowerbike]

lets say you get an average of .020 above the liners.
if you want zero deck you add a .020 base gasket.
if your piston flats are in the hole say .010 you would/could mill the cyl. deck .010 and run no gasket for zero or run a .010 gasket for a -.010 deck or what ever combo your looking for.
it's just simple math.
measure twice..three times and assembly once

 

[Guest]

Ok, I used an OEM gasket spare that I had just to make the math easy. Like Don's, my piston is .020"/.56mm ABOVE the cylinder with the 650 piston/cylinder combo. I'm betting my squish band measurement will turn out to be the same as Don's as well.

Don - would you be willing to make me a gasket just like the one you made for your engine? I really don't have the capability at my house. I guess I could order one from Cometic?

Thanks.

 

[Guest]

Ok, here's my measurements. Like I figured, they are pretty close to Don's.

OEM Base gasket .020" compressed
Deck Height was .020'-.022"
Head Gasket compressed was .044"
.044-.022=.022" clearance.
Measuring clearance using pieces of solder measured .029" averaged

So, looks like I'm too tight as well. The .031" thick base gasket would give me an additional .011" of clearance for a total of .040" if using the solder measurement or .033" if using the piston above deck measurement. I will re-measure both to see why there is a .007 diff.

Does all the above look right and sound good?

Thanks.

 

[Guest]

Ok, I measure everything one more time.

Base gasket .022"
Piston .022" above deck.
Solder laid across piston top - .028" at the flat part of the piston edge.
Head gasket quite thick - .044" compressed.

Now, with all that, looks like for optimum clearance of .035-.040", I need a base gasket that's .027-.029" thick correct?

What's the measurement for "squish"? I read somehwere that ideal it should be .043". Is that the same as the flat part of the piston to head distance?

Can someone double check my math?

Thanks.

 

[blowerbike]

.022+.022=.044
.044 would put you at zero deck...simple math...

 

[Guest]

Ok now I'm confused BB. I may not be a master engine builder, but I can certainly add. The piston sits .022" above the cylinder. How is that zero deck height? Unless zero deck does not refer to the amount of piston above the cylinder...

 

[Suzuki_Don]

Ok, I measure everything one more time.

Base gasket .022"
Piston .022" above deck.
Solder laid across piston top - .028" at the flat part of the piston edge.
Head gasket quite thick - .044" compressed.

Now, with all that, looks like for optimum clearance of .035-.040", I need a base gasket that's .027-.029" thick correct?

What's the measurement for "squish"? I read somehwere that ideal it should be .043". Is that the same as the flat part of the piston to head distance?

Can someone double check my math?

Thanks.

Clay my calculation works out that you would need a .034" or .8mm base gasket.