Potential Group Purchase - Wiseco GS650 741cc pistons

[Chuck78]

Head gaskets - 1.6mm to 1.8mm recommended

Okay so I've done a lot of math and milling over my extensive notes and measurements, stressing about engine variances... best to err on the slightly thicker side to be safe, a light milling can get each engine to tighter quench specs if the builder desires.

Basically, I'm coming up with 0.1mm variances in figures between different engines. This is pretty much exactly as I had stated a while back before I did such an extensive measurements, I always like to triple check my triple checking just to make sure I'm not making any big mistakes on a $1,000 order.








THE GOOD STUFF:

on the tighter side of engine deck heights, undecked block, we're looking at needing:
1.6mm (as ordered, uncompressed) MLS head gasket to achieve .040" quench (1.016mm)

on the taller deck height end of engine tolerances, we're looking at needing: 1.5mm (as ordered, uncompressed) MLS head gasket to achieve .039" quench (0.99mm)

If wanting to deck the block slightly (.006" to .008"???) for a clean true gasket surface, probably want to go with 0.2mm extra head gasket thickness.

The absolute minimum quench anyone with a tight bottom end in my opinion should even consider approaching is .035", or 0.89mm. So if you ordered a 1.5mm but your engine should have had a 1.6mm to get 1mm quench, it would likely still safely run, and very efficiently at that, but that's on the dangerous edge... crank bearing wear and cylinder bore wear / piston rock could change that in time.


To err on the thicker side, figuring the most negative deck height measured (piston protruding above deck surface the most of all examples - .022" w/base gasket), even running as thick as a 1.8mm head gasket would still yield .049" quench, not quite as efficient or as high of compression ratio, but still ineffective quench band. .010" more and it would not really do very much to improve efficiency as a tighter quench band would.


For reference, 0.1mm = 0.004" (.0039 actually)


For now I would say 1.7mm is a very good efficient but safe thickness to run on a GS550/650-740cc hybrid engine. those wanting to deck the block more substantially, perhaps go with 1.8mm? Those not wanting to deck (surface mill) the block at all if possible, go with 1.6mm IF you want to run on the tighter quench side for max performance.


IF you have a complete GS650 engine, the factory 650 gasket I believe was around 1.2mm to 1.3mm thickness, which would require a bit of decking for maximizing quench if the piston is down in the hole the typical .020" or .5mm.

I am pretty sure this is the assumption Charlie / Old Colt was making when he asked me for a 1.0mm or so head gasket. I'm estimating you'd need a 1mm or .9mm gasket on an undecked 650 top and bottom to get decent quench. Err on the safer side though!!! 1.2mm, deck block to suit?





this is all figuring in using stock style (enlarged GS550 gasket for 650 sleeves, or just 650E) base gasket to have the top end oil pressure o-ring sealing between metal & metal instead of compressing against a 650G style (not 650E style) non-o-ring base gasket. I like this idea better, o-ring to block/cyl not o-ring sealing against gasket, making gasket seal oil pressure. The 650G just uses the gasket to seal the oil pressure as well, however... but that is a plain bearing engine which has different oil pressure requirements than the 550 and 650E with roller bearing bottoms

Also I had better check, but I thought I recall perhaps someone, maybe just one of us, was inquiring about ordering these pistons for a gs650 ( almost all of us are doing the 550 bottom the 650 top end, which is why we had these issues come up with deck height and gasket thickness). In that case, they would just need to default to a stock base gasket thickness. I will order at least one like this because I want to mock up one engine with 650 cylinders bored for 750 pistons, same diameter as ours, but using a big Port 550 head instead.

if anyone wanted to do the thicker base gasket route, that is still possible as well.

Also, doing the thicker head gasket / stock base gasket route, you can use a GS650G base gasket, but just need to trim out the holes on the rear outside corner studs to allow use of the 550/650E egg shaped oil pressure o-rings (trace the 550 base gasket if you have one)

[Chuck78]

Crunching numbers all evening here and re-revisiting all of this information.
I am torn between the stock base gasket and thicker head gasket, vs thicker base and thinner head gasket for less compression ratio lost.

With the custom base in thicker size, Suzuki_Don said he simply left the material the same as the 650G gasket - the 650G is a plain bearing engine and does not use cylinder base egg shaped oil pressure o-rings - it just has a smaller cutout for the oil to transfer, & uses some sort of brass restrictor jet in the crankcase oil feed hole, since it is a plain bearing engine which operates on different oil pressure psi than our roller bearing engines.
The 650E & 550 base gaskets have a cutout for the egg shaped o-rings, so that the o-ring seals metal to metal.
In Suzuki_Don's build, he had substantially thicker base gasket by .3mm or 60% thicker, and I believe he used the 650G gasket as a template and allowed the o-ring to sit down in the 550 crankcase recess intended for it on the bottom side, but the top side of the o-ring would mate to the custom thicker base gasket, and not touching the aluminum cylinder block.
In doing this, the O-ring would have to be compressed .020" thicker than it would otherwise, or thereabouts, perhaps the base gasket would compress a little bit more in that area.

I checked into using thicker cylinder base oil feed o-rings, but the GS400/425 & 77-79 750 o-rings were slightly larger diameter, and look to be a real squeeze to get them to fit in the 550 crankcase and base gasket holes/recesses intended for the smaller 550/650E egg shaped oil feed o-rings.
Parts fiches list the GS400/GS750 8V/GS1100G o-ring as 3.05mm thickness. I measured more like 2.7mm on a 5 year old used version.
I measured the OEM new in package 550 oil feed cylinder base o-rings at 2.2mm thickness. I measured Athena brand new 550 versions of the same o-ring at 2.45mm thickness.

I like the OEM method of o-ring sealing metal to metal using stock thickness base gasket. This seems far better, although Suzuki Din and minder have reported no problems with their thicker base gasket stacked version of this sealing method. With the area in question needing to compress an extra .020" or .5mm, with it torqued down that hard, I'm sure it must create a very firm seal against the oil pressure.

I also got the head gasket bore reduced slightly, as we were going 1mm over the 65mm piston size for the head gasket cylinder bore diameter. Well as I've recalled recently, the 65mm piston, after cylinder to wall clearance added to it, dictates a bore of 64.75mm or so. So we can go with a head gasket cylinder bore size of about 65.7mm or so instead of the previously discussed 66mm. This saved us any further compression loss.

So based on Andy's mockup measurements showing piston out of hole .016" after base gasket (tallest of figures I have collected so far), I am thinking 1.7mm (uncompressed) head gasket is so far the best safe bet.
This would give Andy .046" quench height, so he could safely deck .006"-.008" off the block.

Suzuki_Don's findings 7 years ago would indicate that he may perhaps have needed to mill .014-.016" off the deck to arrive at the optimum .040" or so quench. But even on an unmilled block, quench area starts to have an effect at .060" height, with the biggest positive effect being at almost zero piston to head clearance at speed. So .040" + .014" = .054" quench height. Acceptable still, although not considered the ultimate in performance figures. But allows this gasket to be run on stock block deck surface, or block milled as much as .014-.016".

I'll have to continue this in the AM, brain is getting foggy late at night. Up all night last night after getting home from animal hospital, caring for my dog with a head injury. will pick up these thoughts in AM.

[Chuck78]

Okay so I got quotes back from gasketstogo.com for base gaskets, $37 each, which was a good bit higher that I was expecting.

I, personally, am still interested in using the thicker base gaskets, as it will decrease the extra volume added by the head gasket and slightly increase compression, but I don't expect everyone to want to go this route certainly. I requested a second quote for quantities less than 5, and John said that would not change the price, same price for 1 paper base gasket as it is 19.

If anyone gets this sooner, please email me from the link in my profile, not gspm, that inbox is perpetually almost full. My email address can also be accessed from my profile information. Send me an email with your gsu's or name so that I can send out one mass email and get back individual replies. I will be finalizing the thicknesses of gaskets in an email I will be typing up this evening. Choices of thinner for more compression or not resurfacing your block deck surface, thicker if you want to resurface your block deck slightly. And then also option B1\B2, substantially thinner than those if using a thicker base gasket.

[Chuck78]

Can do either as I talked about in past posts here.

Life always happens and I get busier than I planned (the last 2 nights), so I used some of my remaining vacation days and took tomorrow off, 74 degrees blue skies no humidity, perfect!) to spend in the garage and go riding perhaps. Should get some case clearancing and mockups done with the Wiseco pistons. Cylinder is bored. Head is refurbished. Need to re-stock some of my spare 550 engine seals and build one of these suckers!

The good parts are coming soon.

[frankenwabbit]

chuck...with the new hg measurements that you have taken, are we going to have to order different (different from stock gs650 sized) sized base gaskets as well now?

[Chuck78]

I have re-established contact with John at gasketstogo.com yesterday/today, he will send me a paypal invoice as soon as I confirm exact sizes and quantity.
Charlie, I will contact you after I get off work

I will see if I can afford to eat the shipping costs since I decided to spearhead this order and have not done so in any sort of expedient manner since discovering the deck height/compression height discrepancies between the 550 and 650. Until then, I was ready to send payment and get them here months ago, but since then, I was very fearful of ordering them the wrong thickness. And I am a very very particular sono***un, so if I'm not happy with the fine technical details or uncertain they are 100% correct, I can't be happy until that is resolved. I was hoping anyone else would be able to jump in and do some case clearancing, mickups, and measuring, but only 1 person was able to do that thus far and I was hoping to take an average of a few mockups to get more accurate data for thickness specs.
I'm back on this after work.

-Chuck

At this time just return my money, I will run the copper gasket I have here.

[Chuck78]

Old Colt - I will give you your money back and a free head gasket as partial trade for that ported head of yours if you want to part with it. I want to do an experiment on 1 of these five 550 engines I have here, using 550 head 750 pistons 650 block

[Chuck78]

It has been placed at the top of my immediate to do list (as of yesterday, actually!) since no one else is able to get the installed deck height.
Compression height is same between Wiseco and OEM 650, but very different on 550. I paired each combination of pistons together both half installed on the same single wrist pin simultaneously, to arrive at that information as verified.

Colt, your very thin request, as you told me, may require an extra extra thick base gasket, or else machining down piston quench area as you and I discussed.
We need a minimum of 5 ordered, preferably all of them at once, so I was unable to order just 2 or so gaskets

I was really wanting to order after we got a couple of different engines,mocked up, but all summer has gone by now and no one else has been able to get any mockups done other than 1 of us and a thread from 5 years ago.

I will be trying to get my cases dismantled, clearanced for 650 sleeves, and mocked up to verify height/thickness again for better accuracy.

Worst case I will place the order with everyone's guesstimate on thickness or round up slightly to be on the safe side, can always mill the block down, good idea anyway for a fresh surface.

This was a GROUP effort, I was contacting the manufacturer, but needing more data from the GROUP aside from your ultra-thin custom request, because I didn't want to be responsible for ordering too thin of gaskets for everyone.

I am sorry it has taken almost all of us this long and still no additional mockups since June.
I will take a vacation day to do so if I have to!!! I will be building up at least one this winter, maybe 2 or 3.

You can text me or email me for extra motivational push if you feel the need.

-Chuck

I placed an order for a headgasket back in March. I specified a thickness based on an assembled engine utilizing an off the shelf base gasket, the new pistons from the group buy and a new off the shelf 650 head. Why has there been no gaskets ordered?

Is this because people are trying to come up with gasket thickness using factory 650 pistons? They are not the same as the group buy pistons.
Please either supply the gaskets that were promised or return our money.

[tkent02]

Getting closer on the gaskets? My 675cc 550 needs to be bigger.

[Chuck78]

Due to my hectic summer and time constraints (I still have not mocked up any deck heights with the 650/740 pistons on 550 bottom), I was just about ready to pull the trigger on going, off of the only measurements that any of us have gotten, combined with Suzuki_Don's measurements from many years ago. I can still do that if anyone wants to say the word. Basically the variables here would be thinner head gasket plus custom thicker base gasket, vs thicker head gasket and stock 650 base gasket. The other variable would be whether or not you wanted a thicker head gasket to accommodate for decking the block substantially.

Comments?

Sorry for the delays perpetually, I would like to get this off of my plate and have some of these screamers ripping around the globe.

[Chuck78]

I hope to have good updates real soon as I am in engine building mode now...
I've been building up my paypal balance beyond the group gasket purchase amount so that I can order several extra gaskets, as I also plan to try and fit GS750 Pistons into gs650 cylinders with big port BS32 carb gs550 heads and VM28 carbs... onto GS550 bottom ends. Not quite as much hp potential as the 650 closed chamber head, but a budget version.

Has anyone else gotten any mockups for deck height measuring?

[frankenwabbit]

any updates?

Yeah I feel like I make one or two steps forward, then I run out of money. For some reason, I keep running out of that precious green stuff. I might be due to one too many projects.