GT750 breaking in, any recommendations?

[dyrberg123]

Hi guys,

So here we are, crank rebuild, cylinder rebored, new genuine mikuni jets, new electronic ignition and just about to push the start button.

But should i follow the original owners handbook advise or is there a modern better way og braking it in?

One guy told me 100 miles really easy below 4k and then below 5k the next 500.

Others say newer hold same throttle position over longer distance, but remember up and down in speed / revs, with light to modest load.

After all a good seal between the rings and the wall must be what we are looking for.

I will play it safe and put 2%oil in the tank until i am sure all is working.

Cheers

[yeadon_m]

I would not add oil to fuel as it actually weakens the fuel / air mixture and might run lean/hot.
I am told that using non-synthetic 2T aids running in.
I would go light throttle and use the revs suggested.
No idea if Suzuki's running in guidance was more about avoiding warranty claims than in achieving a well run in motor though!
Congrats, by the way and enjoy!
Mike

[Craig380]

My 10 (euro) cents is this - start her, warm her up gently on the stand to make sure everything is running smooth and there are no funny noises.

Then go for a ride. I believe it is important to give a new engine a little work to do within the first 30 minutes / 20 miles. Not full throttle / redline, but like this: in the first few miles, get the bike on the open road in 4th gear, and accelerate using about half throttle from about 3,000rpm to 4,500rpm, then back off the throttle and let the speed and rpm fall back to 3,000. Then accelerate again to 4,500rpm using half throttle, and back off. Not aggressive throttle, but rolling it on gently, and rolling off gently. Do this about 5 or 6 times in total and it will help the 'bed' the rings in.

Then just gradually build up rpm and speed over the next 500 miles or so.

Tilykke with the rebuild, enjoy her

[dyrberg123]

Thanks for the advices,

Craig, what you suggested is more or less what i have learned too, and also what i did with my t350 last time...

I have read somewhere i here on this forum about adding some oil into the tank to play it safe at first, but not sure where...

Thanks

[GT750Battleship]

Hi,take Mike's advice & don't add oil to the fuel tank...can do more harm than good
Cheers,
Roger

[rngdng]

Ride it as you plan on riding it. Baby it and it'll just be slow. I was taught by a wise old Yamaha mechanic in the 70s to redline it day one.....BUT do not overheat it. He used to redline RD350s upon initial startup, unloaded on the work stand. I thought that was too much, but he never hurt one.

I just ride them as I plan to and take it easy for a half hour or so, then go for it. There are as many opinions (and opinions they are...) on this subject as there are on two-stroke oil.....


Lane

[Vintageman]

Ironic how we differ. Well a lot of us here have rebuilt a lot of engines and have their experiences. Here is where mine has brought me at the moment:

If you want to put a little oil in tank for you are nervous about injection . Go for it. Just realize it can confuse you if something off with carbs, such as an assembly mistake. Later I always run a little oil in tank

Now here is what I think I have learned. Run it in easy. I mean break it in easy. Note the work "break" that is what is happening. Nothing it perfect and things need to wear/fit in. If you go too hard that will be violent. Cause hot spots fast. Cause build up and interference areas and fast... then damage. Go easy, vary the load so you "stretch out" all areas.

Next, tear down top end a look for areas where you can help the “fit in” lloking for high spots on piston etc.… . Well you won’t be doing that on the complex GT750 now will you . So instead just run it easy and let it do the fit for you but slowly and softly.
.
It may take a little long to have things seat/fit this way but, not much more and the long term results (if that is your goal) are better IMO

[Coyote]

I asked this same question about starting up my GT550. That should be tomorrow!! I have decided to run 64 / 1 premix for start up BUT, that fuel will be in a separate tank hanging from a tripod standing along side the bike. As soon as the oil pump proves out, it will instantly be switched to straight non ethanol fuel -- in the bike tank.
For the accessory start up tank, I just adapted a hose barb to an old plastic Simple Green jug. I even put a shut off valve on the start up tank so I can shut it off and burn up the remaining oiled down fuel. Whatever is left over will go in my chain saw supply can.
I have reason to be skeptical of the oil pump as this motor had a totally fried left piston. Some of you might remember the pic. I don't need that again. Some minor scuffing

[dyrberg123]

Hi guys

Wow that looks like a hoone doesn't do it.. i will make a aux tank with light premix for initial startup, then run straight petrol when i hit the road.. I believe that craigs suggestion is close to what i have heard, and also close to what i did last time... Thanks for all your advices.. I will use some blendzall 455 ultra, it works as injector oil and is with castor... either that or castrol tts.. like that one too.

[Craig380]

@Coyote - wow, that is one SHOT piston. It's even crumbling away between the ring grooves

[Coyote]

I gave the piston to the owner of a local bike shop, to put on his counter as a conversation piece. I think he tossed it because I've been back there and haven't seen it.. As you can well imagine, the cylinder was shot too. I didn't think there was anything serious wrong with the bike. Then I ran a compression check

[Coyote]

I have a Suzuki manual printed by Suzuki in 1973. It's a GT550 manual that pertains to the J model only. It's sort of a condensed shop manual. It says this about break-in:
First 500 miles - below 4,000 RPM
500 - 1,000 miles - below 5,000 RPM

Seems a bit excessive. Probably one in a hundred ever went by it The temptation was just too much.

[tz375]

If we did that with our race bikes, they would be worn out before they were run in...

The key to it is that revs are OK but watch the load and build that gradually with quick blasts in between.

[dyrberg123]

If we did that with our race bikes, they would be worn out before they were run in...

The key to it is that revs are OK but watch the load and build that gradually with quick blasts in between.

Hi TZ,

please specify quick blasts. Is that wot as a blast or what?

thx