GT550A top end woes

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vulcanman
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Suzuki 2-Strokes: GT550A 1976

GT550A top end woes

Post by vulcanman »

Hi all , im a newbie to here so bear with me .i have a1976 GT550A which i bought last July .she had a newly rebulit engine too and bottom.much of the rolling chassis too .not perfect but very good.have floowed running in procedures to the letter.having had a 380 and a kettle for many years .last Sat on the 550 devloped a death rattle top end left barrel .on stripping found most of the nikasil has worn off and all pistons badly scored .oil supply issues i suspect but need to test oil pump and all feed pipes .however imhaving trouble tracking down any oe std piston sets and someone to re do the nikasil .ive contacted Aptec and awaiting answer on if they can do it .the pistons inthe previous rebuild were Cruzinlines ones which Stan the man says avoid and only use oe ones .any ideas or help be appreciated.by way only oe pistons i could find in uk were at Robinsons at £489 each ! Not even a kit and only had 2 .im thinking of just selling as a non runner as not economical to do .? Cheers bob
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Evans Ward
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Suzuki 2-Strokes: 76 GT750, 72 H2 750, 84 RZ350
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Re: GT550A top end woes

Post by Evans Ward »

Actually, a lot of the Kawasaki Triples guys have had good luck with the crusin image pistons. If needed, I’d go with Wossner but they aren’t cheap.

That sounds like an expensive issue you have with your GT550. Only you can determine your next steps with it. Good luck!

Where are you located? It helps to put that info on your profile for members to make specific recommendations.
1976 Suzuki GT750 (Maui Blue), 1972 Kawasaki H2 750 Mach IV (Candytone Blue), 1984 Yamaha RZ350 (KRR- Yellow/ Black).
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Evans Ward
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Re: GT550A top end woes

Post by Evans Ward »

Never mind, I see the UK in your profile- my bad.... :oops:

I’m sure some UK members will chime in soon. :up:
1976 Suzuki GT750 (Maui Blue), 1972 Kawasaki H2 750 Mach IV (Candytone Blue), 1984 Yamaha RZ350 (KRR- Yellow/ Black).
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jabcb
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Re: GT550A top end woes

Post by jabcb »

Wossner is a German company. They make GT570 / T500 / GT500 pistons. I don’t know if they ever made GT550 pistons.

I have an old Wiseco catalog from 1977.
Wiseco is an American company. They used to make GT550 pistons in standard + 4 oversizes. Piston part # 178PS through 178P8.
They are not easy to find, but Paul Miller might have a set. He is eBay seller jrwdfa. He is US based & I don’t know if he sells to the UK.
His phone # in the US is 860-828-1771. He has limited hours of availability by phone & may be difficult for you to call.

Depending on your budget & skill level, your best bet might be to have one of the UK expert shops fix the bike.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
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Alan H
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Suzuki 2-Strokes: 4 x GT550s - J, M, A, B.
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Re: GT550A top end woes

Post by Alan H »

Barrels are available on ebay and elsewhere - not sure if I have a full set spare now, and currently they are inaccessible due to the amount of crap stuff currently generated from my halfway through kitchen out/kitchen in project.
You can get the nikasil barrels replated and another option is to have the barrels bored and schneurle port liners (same porting as nikasil) pressed in (PJME). I fitted a set to a mate's bike about 18 months ago and they were fine. Similar price to replating, but you can have them bored again.
First job is to find out why. Did you run out of 2T oil or mix different types, or did the pump fail?
I have spare pumps and oil lines and I just might have a set of pistons that would be ok for the job.
Where are you based and what's your biking/mechanical ability?
Nothing wrong with cruzingimage pistons and there's a uk company selling new pistons made in Japan iirc (IMDpistons.com near Chester.)
Bluesmokebaz in Dudley does engine/bike refurbs and is very good - he's just had a spare crank done for me and a couple of others last year for my 2 GT550s.
Last edited by Alan H on Tue Apr 06, 2021 11:49 am, edited 2 times in total.
Think of how stupid the average person is, then realise that half of them are more stupid than that.
vulcanman
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Re: GT550A top end woes

Post by vulcanman »

Thanks Alan , im ok and have great mates helping .2 stroke tank checked on every ride out .is 90% full .running Motul semi synthetic .yes need to check the oil pump and all the lines .Langcourt will do the nikasil and piston kit and gaskets coming from Grampian motors .establishing why is main concern.i did change 2 stroke oil over to mtul as couldnt get the oil it was running on but ran tank down 1st .is that a no no ? Thank to all of you for tips and guidance .
vulcanman
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Re: GT550A top end woes

Post by vulcanman »

Hi Alan im based in East Sussex , abilities ok ish 🤔 .got to rebuild her as love her .just right when you 60 now .
vulcanman
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Re: GT550A top end woes

Post by vulcanman »

I had a Kettle A for 20 years and a 380 and never had any issues apart from crank seals on the 750.hoping to look at pump this week.the nikasil looks as though maybe it didnt take too well or oil not getting through .although pistons are black on top and plenty of oil around .im really puzzled .i have aVFR 750 mk 1 87 so be putting her back on road as sorned her for winter and during lockdown .im now worried about having changed 2 stroke oil ?
vulcanman
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Re: GT550A top end woes

Post by vulcanman »

Have to admit i really think ive done something stupid and really need guidance .
vulcanman
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Re: GT550A top end woes

Post by vulcanman »

Alan would loose top head bolts be cause .i did check and re torque the head at 500 miles to 24lb but on Sat while stripping top end they were not tight .also the 12 top studs have all been nickel plated and once head off found they were all just finger tight or loose but the head didnt appear to be blowing ?
vulcanman
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Suzuki 2-Strokes: GT550A 1976

Re: GT550A top end woes

Post by vulcanman »

This Sat got a mate over to help test the oil pump and check all the lines .if pump has expired crank will be shot too .i dont want to order parts or get barrels nickasiled until sure of cause .bill going up by the second !
vulcanman
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Re: GT550A top end woes

Post by vulcanman »

Hi Alan , if my pump has failed in some way i may be very interested in purchasing one of yiur pumps .
vulcanman
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Re: GT550A top end woes

Post by vulcanman »

On top end rebuild is it best on 1st start up to use a pre mix aswell.was planning on it but not sure .obviously will ensure plenty of lubrication is on pisto s etc .
vulcanman
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Re: GT550A top end woes

Post by vulcanman »

Before 1st start after rebuild is it best to run a pre mix in addition to ensuring plenty of lubrication on pistons etc ?
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Alan H
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Re: GT550A top end woes

Post by Alan H »

After/during a rebuild, I just 'well oil' the parts as they are being 're-mantled'. If you want to use some oil in the petrol as well, that won't hurt, but just use a small test tank with half a pint of fuel mix - no need to use lots.
In the past I left the air box off for first start and gave a quick shot of easy start into each carb before hitting the button, and use a set of B6ES plugs (hotter than standard) too. If one pot drops out, another quick shot of easy start will usually bring it back on line. When the fug clears and the engine runs properly, put the next grade of plugs in and fit the air filter before the first ride.
Mixing oils. If you mix different types, this can cause issues as mineral and fully synthetic mixes can clot and block the lines, but if I change oil then I run the tank low and drain the last bit. Put some fresh in and start the bike with the oil pump arm moved to fully open. Yes it'll smoke, but it will also pump the new oil through faster.
Cylinder head nuts/studs. If I've had the studs out, I put a drop of studlock on the threads before fitting them, and 'double nut' them so they are tight. When the head is fitted each stud should have a flat washer, spring washer and nut on. I suspect that you don't have spring washers fitted, or perhaps they are old ones? New ones are cheap enough and so are nuts - they are fine thread, same as barrel base nuts. Not sure why anyone would nickel plate the studs - no-one can see them!
Make sure the tank oil level drops after a ride - easy way is to fill to the bottom of the filler neck with the bike on the centre stand, then you can measure how much you put in after (say) a hundred miles. My 550s tend to use about 700 miles per litre depending on use.
Checking oil lines. A bit of a faff, but take the carbs off, then remove pump and lines (the spider). Use a syringe to squirt oil down each line and make sure it comes out of the engine end. When you've done them all, hang the spider up (pump end up) and see if any of the lines leak overnight. If they do, the valves will need stripping and cleaning.
DO NOT USE COMPRESSED AIR ON THE LINES OR YOU'LL KNACKER THEM!!!
Have a look on the oil pump arm and there will be a number - that's the pump type. They'll all work, but best to use the right one.
More pump info here - https://www.oldjapanesebikes.com/mraxl_ ... s/page-A57
Think of how stupid the average person is, then realise that half of them are more stupid than that.
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