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 Post subject: GT550 Engine Rebuild
PostPosted: Mon Jul 03, 2017 9:58 am 
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Still in the Driveway

Joined: Mon Jul 03, 2017 9:51 am
Posts: 6
Country: UK
Bikes owned: GT550 , RG500
Hi everyone. Just joined the forum with my newly acquired '74 GT550. Took my first real spin on the bike yesterday and it seems lacking in power. The bike has not done much mileage recently and I guess a full service will be needed. However at some point I'd like to get a full engine rebuild including get the cases vapour blasted. Anyone got any recommendations for someone ot carryout this work ?? Preferably in the North West of England but can travel.

Thanks very much.


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 Post subject: Re: GT550 Engine Rebuild
PostPosted: Mon Jul 03, 2017 11:19 am 
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World Superbike
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2096
Location: The Republic of South Yorkshire
Country: England
Bikes owned: GT550s GT750 GSX1400 and lots of spares
Check timing, plugs, carbs first and do a general service. Why should you need a rebuild? These bikes are ove 40 years old now, and at best only have just over 50bhp at the crank when new. Early ones a bit less. Get classic motorcycle mechanics for people local to your area for blasting etc. But have you realised how much it will cost? Media blasting your cases means a total strip when it may bot be needed unless you're VERY careful and know exactly what you're doing.


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 Post subject: Re: GT550 Engine Rebuild
PostPosted: Mon Jul 03, 2017 1:51 pm 
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Still in the Driveway

Joined: Mon Jul 03, 2017 9:51 am
Posts: 6
Country: UK
Bikes owned: GT550 , RG500
Thanks Alan - yes Im not expecting rocketship performance but yesterday it struggled to hold 5th gear on the flat. Assuming the gearing is standard - I would have expected a bit more. Ultimately I want to repaint the frame and cycle parts so the engine wil be coming out. I realise it wont be a cheap job to do. I'll give it a full service and check the ignition and carbs but being a pessimist I'm bracing myself for an engine rebuild. Its not s job I really want to do myself so looking for a good specialist. Cheers Eamonn


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 Post subject: Re: GT550 Engine Rebuild
PostPosted: Wed Jul 12, 2017 4:45 am 
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Moto GP
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Joined: Fri Oct 24, 2008 5:55 pm
Posts: 3972
Location: Lancaster Pa.
Country: US
Bikes owned: GT750 x2 97 -1200 Bandit 86 GSXR1100
Almost sounds like it wasnt running on all 3 cyl ?

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the older i get the faster i was


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 Post subject: Re: GT550 Engine Rebuild
PostPosted: Wed Jul 12, 2017 6:18 am 
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Still in the Driveway

Joined: Mon Jul 03, 2017 9:51 am
Posts: 6
Country: UK
Bikes owned: GT550 , RG500
Hi - no it seemed to be running on all 3. Smoking away and running pretty smooth. It revs out ok just no pulling a load as well as I expected. Think a compression test is on the cards.
Might be even something daft like gearing - it seems to struggle in top gear.


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 Post subject: Re: GT550 Engine Rebuild
PostPosted: Wed Jul 12, 2017 6:29 am 
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Moto GP
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Joined: Fri Oct 24, 2008 5:55 pm
Posts: 3972
Location: Lancaster Pa.
Country: US
Bikes owned: GT750 x2 97 -1200 Bandit 86 GSXR1100
If it has the couplers on the pipes it can fool ya in looking like all 3 are running . Check the temp on the down pipes to see if they are the same temp . The baffles can get pretty clogged up to lowering power .

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the older i get the faster i was


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 Post subject: Re: GT550 Engine Rebuild
PostPosted: Thu Jul 13, 2017 3:15 pm 
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Still in the Driveway

Joined: Mon Jul 03, 2017 9:51 am
Posts: 6
Country: UK
Bikes owned: GT550 , RG500
Good point Dave with the exhausts !! Never thought of that with the linked pipes. That said it seems pretty smooth and I'm fairly sure its running on all cylinders - a compression check is needed, and a look at the plugs at the same time might reveal something - thanks for the advice.


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 Post subject: Re: GT550 Engine Rebuild
PostPosted: Thu May 10, 2018 2:46 pm 
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Still in the Driveway

Joined: Mon Jul 03, 2017 9:51 am
Posts: 6
Country: UK
Bikes owned: GT550 , RG500
Been a while but too many projects on the go !! Bike still running ok but its defintely down on power - finally did my compression test last week - around 70-75psi on all cylinders !! That sounds like a rebuild is defintely needed. Am assuming rings at the very least - hopefully nothing too bad but wont know till its opened up. Anyone used the Cruz pistons advertised on ebay ?
Cheers
Eamonn


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 Post subject: Re: GT550 Engine Rebuild
PostPosted: Fri May 11, 2018 1:10 am 
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Expert racer

Joined: Mon Dec 01, 2008 2:52 am
Posts: 1100
Location: Manchester, UK
How did you do the compression test? Was it with the engine still hot (5 mins after a ride), throttle held wide open, and taking the highest reading after 8 to 10 fast, hard kicks on the starter? If yes, then 75psi means at least new rings, and probably a rebore. If you didn't do it as I described, then the reading will not be correct.

You should see at least 120psi and no more than 10% difference on any cylinder.

Also, with Suzi factory exhausts, the removable baffle tube is almost never the problem. Heavy carbon deposits build up in the body of the exhaust and rob power. You need to take the exhausts off the bike, and basically assault them: hit the seams of the pipes hard with a rubber mallet to dislodge crap, poke tubes up to dislodge more stuff, fix an old clutch cable into an electric drill and stick the frayed end into the pipe from both ends to 'scarify' the inside of the pipe .... you'll be amazed at how much crap you'll get out, and how much better the bike will go.

Pay particular attention to the area where the header is welded to the main pipe, this attracts a big ring of carbon which becomes a restricter.

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1976 GT380 - wounded by me, and sold on
2006 SV650S. It's got cams, and valves, and stuff


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 Post subject: Re: GT550 Engine Rebuild
PostPosted: Fri May 11, 2018 2:54 pm 
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Still in the Driveway

Joined: Mon Jul 03, 2017 9:51 am
Posts: 6
Country: UK
Bikes owned: GT550 , RG500
Thanks Craig - yes compression test carried out properly. Think the heads need to come off for a look - good advice for the exhaust but am thinking of a set of Higgsspeeds


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 Post subject: Re: GT550 Engine Rebuild
PostPosted: Mon May 14, 2018 12:59 am 
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Expert racer

Joined: Mon Dec 01, 2008 2:52 am
Posts: 1100
Location: Manchester, UK
Unfortunately, it looks like a head & barrels off job. Let us know what you find.

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1976 GT380 - wounded by me, and sold on
2006 SV650S. It's got cams, and valves, and stuff


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