Potential Group Purchase - Wiseco GS650 741cc pistons

[Chuck78]

If you want to build more compression by not losing it with head gasket bore volume (thicker head gasket, gasket bore is larger than our 65mm cylinder bore), then it **might** be a better idea to run a 1.3mm head gasket and add .3mm to the base gasket thickness.
That would give you the same quench height as stock OEM base + 1.6mm ordered / 1.5mm compressed head gasket.

I am really needing to get this Wiseco 610cc GS550 rebuilt and out of my shop space so I can tear into the 77 550 donor engine and measure my deck height!!! Almost there... I want to get the block skimmed more than .003" just in case, which is about all I'd skim yours Andy if you order the 1.6mm head gasket.

.1mm head gasket thickness additional means .1mm or about .004" to skim off the block if mine is the same as Andy's block height and installed deck height.
So If those were my measurements, I'd go 1.7mm (stock base gasket or equivalent head gasket using .8mm base) so that I could have .040" quench distance and be able to mill .007" off the top of the block deck if necessary.

Thoughts????

[Ace07]

How doesn't surfacing the head affect squish band? If you take material off the surface of the head it will move the pistons closer to the head chamber. How is it different than surfacing the cylinders?

[Chuck78]

How doesn't surfacing the head affect squish band? If you take material off the surface of the head it will move the pistons closer to the head chamber. How is it different than surfacing the cylinders?

Because the squish band is the distance between the flat surface of the head just outside of the combustion chamber to the flat surface on the edge of the piston's top, next to the dome. if you were to look at the 650 head after you removed it, you would see carbon or some other markings that show you that the head gasket bore is much larger than the combustion chamber (especially on a closed chamber heads such as the 650), and if you measure the combustion chamber, it is substantially smaller than the bore of the piston. The squish band is the distance between the two flat surfaces at top dead center.

some older bikes and models like the gs550 do not have a quench area to measure the squish band from, the 550 piston is 100% dome, no flat area on the top, & the combustion chamber mirrors that. a lot of older Hondas are like this from what I gather. The quench design is more efficient than the full hemi bore / full sized chamber.

the only thing that surfacing the head affects like I said is piston to valve clearance, & cam timing (the chain is shorter distance between the crank and cams). And compression ratio of course.

on major head resurfacing, if you had high domed high-compression pistons, you would need to be concerned about the piston dome contacting the chamber.

[Ace07]

How close are we to ordering these gaskets?

[Chuck78]

so far we've only got two deck height measurements, I should be finished with this bike I'm working on tomorrow and can pull out the 550 engine and measure my own deck height after dismantling & clearancing the case
I've been meaning to compare your deck height measurements to Suzuki Don's:
Posts 132 through 150ish+

http://www.thegsresources.com/_forum/showthread.php?164443-Camshaft-Top-End-Rattle/page4

Wife is mostly around the Midwest next 8 weeks so I'll be getting more pressure from her to get her "superbike" (the 1st of 2 550 builds here) done... I will definitely be needing these gaskets soon!

Doesn't appear that anyone else has as much priority placed on it as you and I Andy, but sheesh I'm sitting in a garage now filled with 9 bikes & 6 spare GS engines, 2 Rickman bikes in basement, 2 more GS engines and 2 do are Suzuki 250 Enduro engines... lots to keep me busy here!!! 1 more bike coming in for service from a friend, too! May as well put up a mailbox at the garage door!

[Old Colt]

So what is the status of the gasket order? I paid for a gasket on March 28 and it appears this order is not going to be done.

[Tooheys]

How close are we?

I paid for 2 on The 19th of March.

[Chuck78]

I'm back on it as of now, sorry have not been getting email alerts on my phone for some reason. The biggest hangup is we have only managed to have 1 person mock up deck height so far and provide hard measurements to properly order from, a second or 3rd comparison would be very helpful due to machining tolerances and variances.

I'm going over this stuff again. I have all afternoon and this week evenings to do this, GS750 cylinder head swap, Kawasaki KDX Wiseco piston kit / carb rebuild / tubliss system and tires...

Going to be crunching some number comparisons right now vs Suzuki Don and Sci85's figures from years ago. Hope to do my own real world mockup in next few days.
Sorry for delays but waiting for you or any of the others involved to pool more deck height data together as has been stated this entire time. The more accurate, the better.

Thanks,

Chuck

[Chuck78]

I now see that I have 2 angry posts before this, not just 1.
Once I discovered info that led me to check compression heights of 650 vs 550 pistons, & then realized we can't go with OEM head gasket thicknesses or thereabouts, I put a screeching halt on ordering and asked for more mockup data from all those involved.
Andy ordered these pistons through a very long process and lots of time on his own at zero charge to you all. I am trying to get an accurate head gasket thickness order together as well at zero cost to you. When I realized we need to do some more research almost on a case by case basis due to different engine machining and tolerances, I reached out to all of you for you to each get your cylinders bored and deck height mockup measured. I have gotten Suzuki_Don's from his build threads many years ago, & 1 other good set of numbers.
If you are all okay with me ordering based on those two sets of data alone, I can place the order any day now. The funds have all been sitting in my PayPal account since day one waiting, & gasketstogo is on standby to commence production for us.

Sorry I haven't been driving this harder but my life has been a hectic mess and most of the others involved have been non-respondent when I have asked for more data or ANY feedback.

Re-visiting the deck height numbers again right now.

[Chuck78]

Okay... based on Andy's 2nd set of (fully torqued) deck height figured based on my previous posts, to achieve a hair over 1mm quench /squish band (.040"), he would need 1.55mm uncompressed head gasket thickness with stock base gasket OR 1.25mm head gasket and custom .8mm base gasket.

We can only order in 0.1mm increments, so 1.5mm or 1.6mm head gasket if he is using stock base gaskets.]So going off of a minimum .038" quench height spec, a 1.6mm uncompressed head gasket on Andy's particular machining tolerance spec engine would allow .05mm-.07mm of cylinder block decking to machine it perfectly smooth and still be within minimum street bike quench specs.

Re-visiting Suzuki_Don's findings now...





Don's detailed findings 7 years ago with detailed measurements:
Uncompressed OEM .048" head gasket and .020" base gasket came up a minimum of .010" short on deck height if shooting for minimum .038" quench (he only got .028" with OEM gaskets after gasket install and compression).

Veteran race engine builders said .035" is the bare minimum and closer to .040" quench is better for street bikes.

Sooooo....
Don's findings say:
.058" (1.47mm) head gasket + OEM .020" base
-OR-
.030" (.076mm) custom base gasket + .048" (1.22mm) head gasket will give .038" quench height.

we seem to gave a .1mm discrepancy here between 2 different 550-650-740cc engine mockups.... likely just die to factory machining tolerances or possibly Andy Ace's block was decked once or crankcase machining tolerances were a bit different.
my crude 550 deck height measurements and comparison of 550 vs 650 cylinders and pistons seemed to support needing .3mm more than OEM gasket thicknesses.

easier to err on the thicker side and mill the block .1mm and arrive at perfect deck height AND a perfectly clean smooth gasket sealing surfsce...

Thoughts? Those were Don's .048" measurements on both a brand new Suzuki OEM head gasket and a used previously installed OEM head gasket that was installed/compressed/run for some time/removed
Perhaps composite gaskets don't compress as much as MLS spring steel shim gaskets?
Again, better to err on the thicker side as we can always have the blocks decked more.



Old Colt, I do remember/realize you wanted ultra thin .8mm or 1.0mm (?) head gaskets due to the fact that you wanted to machine down the quench area of the pistons to adjust quench height so that you could get the absolute maximum compression ratio.


Can anyone else add to this discussion in terms of decision making?

[Chuck78]

I'm adding one more gasket to the order in 60mm bore & 1.3mm thickness, as the Wiseco 610cc GS550 is leaking a bit of oil from the head gasket at the cam chain tunnel in front and the left side head stud oil passages.
The owner is very very pleased with the performance of the bike however, & it was an absolute blast for me to tear around on while test riding, with fresh ultra grippy Shinko 230 tires and a bit less weight than my menacing 920cc 480lb '77 GS750 - I twisted my ankle from clipping my toes hard on the pavement leaning over real far in a turn on the GS550-610cc to give you an idea of how much fun I was having on a buddy's/customer's hot rodded GS550... 610cc was quick enough I suppose, gets to 99mph pretty fast, but I'm spoiled with the 920cc... makes most other bikes/riders seem very slow!
I just picked up another D.I.D. 3.50x18 rim laced onto a GS1000 rear wire spoke hub, & I think I'm going to build up my $300 78 GS550E as nearly a clone of my '77 GS750B, but with the sought-after GS450S Sport model knee dent gas tank. I never had any complaints with the handling of my big 750, & very few friends could keep up with me in the twisties with me on my modded out 750-920cc, but the weight of the 550 felt even more inspiring! I think with a quench and compression optimized 740cc Wiseco 650 closed chamber head setup and perhaps some MegaCycle cams, GS500F 37mm forks & 310mm single disc or perhaps Honda VTR1000 Superhawk 41mm cartridge forks & 296mm dual discs, or 43mm RF900R cartridge forks and dual 310mm duscs... Fox Street Shox, wide alloy rims and big tires, MAC 4:1 & Kerker aluminum system K muffler...& GS1100E aluminum swing arm and GS550 rear disc caliper with 1990 1100G Katana floating right front rotor on the rear...frame bracing added behind the egnition coils at minimum... this will be one AWESOME GS550 for the twisties. Maybe my VM29 smoothbore carbs, if not them then the VM28 accelerator pump carbs I have here.

If I do rebuild the wife's 550 as planned, it's getting Fox Street Shox that I bought for it, has Excel 3.50x18 rear rim and 140/70-17 tire already, probably lace a 2.50x18 Excel front rim up as well in place of the steel 19" stocker and add a 100/90-18 or 100/80-18 tire up there to continue in helping her feel comfortable touching the ground flat footed with short legs (& quicken up the steering a bit more), 310mm twin pot front brake mod, perhaps cartridge emulators. Re-upholstered stock seat shaved down to suit a 5'2" rider and look more stylish. And she requested ditch the superbike bars and put her clubman bars back on...
She defected to a fat pig of a slopoke 640lb 58hp 98mph top speed slow accelerating ill-handling no-brake-having 1986 Harley FXR 1337cc grandma&grandpa slopoke cruiser, so I haven't been too thrilled to wrench on her GS550 since that huge disappointment. Hopefully things change on that front when she comes back around from the current state of events here in my household. Tweaking a 1974 Rickman dirt bike for her to ride comes first though.

good things to come out of my garage real soon...

[Tooheys]

Chuck,

my post wasnt meant in anger sorry.

from your calculations it looks like a 1.3mm gasket is shooting for the middle ground and we can adjust with machining to allow for manufacturer machining differences yeah?

i don't have my 650 head yet so I can't mock anything up I'm sorry.

[Chuck78]

1.3mm is not the middle ground, 1.3mm would require a thicker 0.8mm custom base gasket.1.3mm would definitely not give you adequate quench height

1.5mm head gasket with stock base would be the absolute minimum required from the 2 bikes worth of numbers I was working off of. That would allow no room for block decking. 1.6mm head with OEM base (or 1.3mm head + custom .8mm base) would be what you want if you want to do a tiny amount of block deck machining to mill it down to a fresh clean sealing surface

[Chuck78]

I'm torn between stock base and thicker MLS head gasket, vs .8mm custom base and thinner head gasket (more compression, more power, slightly more efficient with less gasket volume.

[frankenwabbit]

I'll go with the best recommendation for head gasket and base gasket setup.....this will be my first ever motor build. (so ummm maybe middle of the road spec figure?)