Gs550 To 650 Conversion

[Guest]

I am doing the 650 top end conversion to my GS550B ('77) model. I have purchased the cylinder barrel and head. Unfortunately the cylinder barrel is 0.75mm O/S and no pistons came with the cylinders. My chances of finding a used set of pistons is very unlikely. Is it OK to have the cylinders resleeved for whatever 650 pistons I can locate. And is resleeving very expensive.

Once I have the cylinder/piston problem worked out, I then need to find a cylinder head combination that will work. The people that have done this conversion previously have used the 650 head and as they have had a later model 550 their CV carbs have gone straight onto the head. The head I have on my bike presently has 22mm VM carbs. My question is will the 550 head fit the 650 cylinders and what will be the result of running a 650 capacity with 22mm carbs. The standard CV carbs for the 650 are 32mm. Will the 26mm VM carbs off the 750 fit the rubber boots on the 550 head. BTW the intake and exhaust valves on both heads are the same.

Someone has said somewhere that fitting the 550 head with 650 pistons will give too high a compression ratio. What do you think.

Does anyone know if the valve cover and cam chain tensioner off the 550 fit the 650 head (remembering that the valve cover on these models houses the tacho drive and the alignment with camshaft gear must be acceptable) and barrel.

BTW the 650 head that I have has shims in it that range from 2.75 to 2.90, does this indicate the head has not had a lot of miles on it.

Sorry for being so long winded and hope there is some help out there. And that I have posted this in the right section.

Cheers. Don.

[hampshirehog]

Don, you're into all sorts here. I dunno about your part of the world but it would be cheaper here to hunt down a set of pistons, even if that meant with another block, than going for re-sleeving. By the way, how do you know your bores are .75 OS?

I'm not sure about head compatability as the memory is fading but you'd be a lot better off sticking the 650 head on the 650 block as it'll breathe better. The 750 carbs won't fit the 550 boots.

You're probably correct to assume if you've got fat shims that it's low mileage, though it's not a cert.

[tkent02]

Why not bore it and fit a set of 750 pistons?

650 barrels will go that far.

[Suzuki_Don]

Why not bore it and fit a set of 750 pistons?

650 barrels will go that far.

Are you sure? Can you give me some more information? What about deck height, piston pin to ring measurements, are they the same? Iknow if I bore the 650 barrel to 1.0mm O/S it gives me 700cc (698 to be precise).
Thanks. Don.

[tkent02]

I read a thread here a while ago, someone did a 550 engine with 650 cylinders bored for 750 pistons.
Have not done it myself.
I have a set of 750 pistons sitting here, I can measure anything on them you want.

[Suzuki_Don]

[quote=hampshirehog;805467]Don, you're into all sorts here. I dunno about your part of the world but it would be cheaper here to hunt down a set of pistons, even if that meant with another block, than going for re-sleeving. By the way, how do you know your bores are .75 OS?

I know the bore measurement on the 650 barrel I have purchased because I have miked it. It is just a shame that the guy I bought the barrel off did not have the pistons for it. Even with pistons the next drama will be to find rings for these pistons or use the 2nd hand ones that come with the used pistons. These 650 models were only produced for 3 yeaars so are not really thick on the ground. Any help appreciated. Although I looked up the Wiseco site and they seem to have a good selection of piston rings although I don't know if they are for Suzuki OEM pistons or for their own pistons.
Cheers. Don

[Suzuki_Don]

I read a thread here a while ago, someone did a 550 engine with 650 cylinders bored for 750 pistons.
Have not done it myself.
I have a set of 750 pistons sitting here, I can measure anything on them you want.

OK. I'll keep that in mind. This could be a slow project so you mightn't hear from me for a while. Thanx again. Don.

[Fishman]

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=380019369488&ssPageName=MERC_VIC_RCRX_Pr4_PcY_BID_IT&refitem=380018925480&itemcount=4&refwidgetloc=closed_view_item&usedrule1=CrossSell_LogicX&refwidgettype=cross_promot_widget&_trksid=p284.m183&_trkparms=algo%3DCRX%26its%3DS%252BI%26itu%3DUCI%252BSI%26otn%3D4

650 cylinder, pistons with rings for sale on ebay. Not mine, but I happened to see it.

[Suzuki_Don]

http://cgi.ebay.com/ebaymotors/ws/eB...2BSI%26otn%3D4

650 cylinder, pistons with rings for sale on ebay. Not mine, but I happened to see it.

Thanks Fishman.
Cheers.

[Suzuki_Don]

I read a thread here a while ago, someone did a 550 engine with 650 cylinders bored for 750 pistons.
Have not done it myself.
I have a set of 750 pistons sitting here, I can measure anything on them you want.

TKENT02 can you measure the distance on the 750 piston from wrist pin to top of piston. Let's say from centre of wrist pin to the top of the land above the top ring. Not to the top of the crown. Are the 750 pistons you have off a 2 valve or 4 valve motor.

Do you know or can anyone find out for me the thread on the chap who bored out the 650 barrell to fit 750 pistons.

Cheers. Don.

[waterman]

S_Don,
I believe it was Skreemer, brveagle, and/or nerobro had performed a 650/550 transplant. Try a search, I know it has been awhile. Maybe this one: http://www.thegsresources.com/_forum...ad.php?t=84029
I have thought about a 650 transplant but don't feel compelled to do it to the L model that I have. My big stumbling block is the difference between the 650g shaft motors and the 650e chain motors. I believe that the 650e are very similar to the 550; clutch gaskets, oil pan gaskets swap. Likewise, the e heads have 20 teeth between camshafts while the g models have 21. This concerns me since 650 head gaskets are identical. One other concern is that the g models uses plain bearing crank with higher oil pressure, not sure how well 650 g head would work with lower pressure 550 oil pump.
In your case, Ebay is still your friend. I have purchased pistons, cylinder, and head for less than $60 to my door. I would try to stay near stock 650 for ease of tuning, meaning stock CV carbs. If I remember correctly, the member with the overbored 750 was having a lot of difficulty with tuning. The 550 bottom end could easily take the horses.
You will most likely need to get exhaust, carbs, and whole 650 topend for swap. If I remember correctly, the bottom end needs a little metal removed to fit the 650 liners near crank.
I currently have a completely disassembled 650g in garage awaiting a part or two before getting slapped together. I am sure the 550 valve cover will not fit correctly. Need any answers or pics of 650 ask away. Maybe will get to motor this weekend.

[Suzuki_Don]

Thanks WATERMAN. You have highlited a few things that I need to check. I noticed that the bike that NEROBRO worked on was a GS550E which is the same bottom end as my 550 and he fitted the top end from a GS650GLX which I think is the "G" shaft drive model. They gave no indication that the oil pressure was not enough getting up to that head. Also if using the 650 camshafts you need to use the cam sprockets off the 550 motor with 30 teeth as the number of teeth on the crankshaft that drive the camchain is 15 and you know the rest. But I am using the 550 camshafts in the 650 head, they bolt in just fine and they have more overlap and earlier opening than the 650 camshaft which will give the motor even more punch. Any further comments let me know. Your earlier comments made me research some more things to make sure I am getting it right. BTW if you overbore the 650 cylinders by 1.0mm for the 4th oversize pistons you end up with700cc's (actually 698cc) close enough. That should be enough for me.

Cheers. Thanks. Don.

[SAN]

650 conversion

SD, yes thats because the 650e is674cc like the gt. ive heard there was a oil presure problem with the upper end until 83. what is diff or what was changed i dont know. ive think i remember hearing to use the honda or kawasaki 750 piston for a 750 conversion.the 82 kz is 739cc, only 650 cyl & head are compatable because of the tdcc head config on the e .valves are same size as 81,82 550 the intake oring for 81 is 38mm compared to your 28mm size. and 650e plugs are 12mm thread. i have a 81 cycle magazine w/test on 650ex compare diff and similarity to 550.SAN

[Suzuki_Don]

SD, yes thats because the 650e is674cc like the gt. ive heard there was a oil presure problem with the upper end until 83. what is diff or what was changed i dont know. ive think i remember hearing to use the honda or kawasaki 750 piston for a 750 conversion.the 82 kz is 739cc, only 650 cyl & head are compatable because of the tdcc head config on the e .valves are same size as 81,82 550 the intake oring for 81 is 38mm compared to your 28mm size. and 650e plugs are 12mm thread. i have a 81 cycle magazine w/test on 650ex compare diff and similarity to 550.SAN

Hi SAN thanks for the comments. They are all worthwhile and useful to me. What do you mean by tdcc. Are you saying there is a difference in the E and the G head, the parts fiche shows them both as the same part number. Do you know what the oiling problem was? The valves in my 550B '77 model are the same as the 650 valves, but I reckon the 650 has larger and better porting. If you could scan that article in the '81 Cycle magazine I would appreciate it. My email is in my profile if you need it. I also notice the "G" model has slipper big end bearings compared to the roller bearings for the big end in the "E" model. There was a change in cylinder head at eng. no. 103561, but my head is from'83 and is a number starting with118---, so hoping my head will work ok.
Cheers.
Don