Holy Cylinder Block!

[tz375]

Couple of things.

First off, most people do not use a mill to bore a cylinder. It has been done, but the correct way is to use a special boring machine and it is usually centered on the existing bore. http://www.ebay.com/itm/Kwik-Way-FL-AC- ... 2490730206" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

Bores on GT750 blocks are usually off from where we would expect them to be - stock. And boring say 1mm o/s if it was way out of place could only be at most 1mm out of place in an extreme situation, so that is not the main issue here.

Unlike some motors, say Honda for example, where the cylinder block is machined and then the liner is pressed into place, a GT750 liner is cast in place and that is not as accurate for placement. That, I believe, is why GT750 liners are always off and some are worse than others.

In addition, it would appear that heads and barrels are not machined consistently and some are a worse mismatch than others. In the majority of cases, head gaskets are a poor fit with bolt holes frequently out of place and they are grossly oversized for the bore.

If you found a replacement block, it would be interesting to bore those cylinders 1mm and 2mm oversized to see when the boring bar starts to break through.

[Drewski]

If you found a replacement block, it would be interesting to bore those cylinders 1mm and 2mm oversized to see when the boring bar starts to break through.

I was thinking the same thing...well almost. I would like to cut them down the centre If I can find a replacement, I definitely will investigate further

I'm still not sure if the thickness of the sleeve showing at the top of the cylinder is the same all the way down. I seem to remember reading that sleeves are "finished" at the top in some way, at least when they are replaced by pressing into the cylinder. I'm not sure what this entails, I may take the block to a well known borer in the UK that makes new sleeves. I notice LA Sleeve in The States sell replacement sleeves for the GT so presumedly they can be replaced?

[Drewski]

If you scroll down to the bottom, there's a video of the very machine that was used to rebore my block here..and the lovely bloke who did it. They specialise in vintage agricultural engines as well as old bikes, (mainly British).

http://www.cambridge-rebores.co.uk/serv ... nditioning" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

[tz375]

There is a cross section in the FSM that shows the section shape. It's the picture of where to measure wear.

Liners are thinnest at the very top.

[Drewski]

There is a cross section in the FSM that shows the section shape. It's the picture of where to measure wear.

Liners are thinnest at the very top.

Ah great...thanks, I'll have a look

What's your thoughts about the feasability of fitting new sleeves? I know it's not going to help much with my block, 'just curious.

[Drewski]

Do you have a Facebook account ? there are a bunch of nice GTers living in the UK that are on this site maybe they can help ya out locating a cylinder block in good shape https://www.facebook.com/groups/26261717446/" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

Big thanks for this tip Dave...one of the guys on there pointed out a respectable looking block with meaty sleeves in the US, ('sure I checked there )................ that I now own

Mechanical seal arriving presently so the bottom end can "get shut"..........all systems go....again

http://www.ebay.com/itm/291738869087" onclick="window.open(this.href);return false;

[tz375]

.....What's your thoughts about the feasability of fitting new sleeves? I know it's not going to help much with my block, 'just curious.

It is an excellent way forwards because it allows you to fit custom nicasil plated (after fitting) aluminium sleeves ported to your own specs. While the thick iron liners are out you can also take the time to weld up the edges of the transfer ports so they can be ported even wider and you could even add an exhaust bridge and additional transfer ports, auxiliary exhaust ports and put a shaped divider in the transfers. And you could add material to the top corners of the exhaust ports so you don't break through when you raise them and square them up.

All for the same price as a new bike or so I would guess.

[Drewski]

Sounds like fun

Many moons ago...and you may be able to settle an old, (and now totally redundant), argument here.....when I was a 17 year old trainee mechanic at a small bike shop in the UK, the head mechanic had a GT750, (A or B) and he had spent a small fortune on this bike. Everything that could be had been chromed, King & Queen seat, custom sporay job the usual home garage custom job. I can't remember what the motor looked like, but this guy said that the engine had been bored out to either 800 or 850cc, (memory fails me somewhat there). Everyone called BS on this as it was "well known" at the time that the water-jacket restricted how far you can go. He said the barrels had been worked on by a company called Barton and stuck to his story. His best mate, had a virtually identical bike and they used to ride around together, both doning their Chromed German army helmets and chain covered jackets:D

What do you reckon? True..or false?

[Suzukidave]

Barton would have been the company to do it , there was another shop that punched them out to 900cc

[Drewski]

Interesting, did they re-sleeve the original block?
The GT in question did a claimed 145mph, no mean feat back then for a "road" bike..but what impressed me the most when I went on the back once were the brakes. IIRC he'd fitted brembo brakes, may have even been a rear disc. At that time I hadn't owned a disc braked bike and was stunned how quick this thing stopped from top speed

How I wished we had digi-cams back then, I have very few photos of that era

[Drewski]

Ah just seen this:-

Barton Motors didn’t just make their own engines. They also modified many types of racing engines. Barton Motors offered mods to private owners for the Suzuki GT 750 which had established itself in F750 racing. Barton Motors offered four different stages of tune which resulted in the engine producing up to 115bhp. The conversion was extensive and included, keying the crankshaft tp prevent twisting, the insertion of spacers on the crank in place of oil thrower plates so that petroil could reach the main bearings, while big-end bearings were made fully floating to prevent seizure. A dry clutch mates the engine to a six speed gearbox and ignition is by Krober or the cheaper Femsa alternative. Barrels were re-worked and could be sleeved for ease of repair, heads were modified, and a floating exhaust system with expansion boxes was allowed to resonate on flexible stubs. The 750 development brought Barton Motors closer to Suzuki and they re-sleeved barrels for the Works racers and also manufactured replacement parts.

http://yorkshireferret.blogspot.co.uk/2 ... -more.html" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

One thing about this guys bike though.....I could be wrong, it was about 40 years ago, but I'm sure both his and his mates bikes had standard pipes Surely if someone goes to the trouble of having the block reworked, they'd at least fit expansion chambers?

[tz375]

Barton did offer a range of parts for GT750s and supposedly did barrel repairs for Suzuki GB. They used Cooper rings to seal the heads and offered liners and all manner of other parts.

That article is pretty old, but I agree that it is extremely unlikely that anyone hid a full on Barton motor under a set of stock OEM GT750 pipes. That would be a complete waste of time and cash and the latter is not going to happen with a Yorshireman.

[Drewski]

Replacement block has been blasted and I've got more rot it's nowhere near as bad though, the base and top I'll have skimmed not sure about the exhaust port, I may just get away with no leaks as is

[tz375]

That rot is all your own fault for cleaning it properly and looking....

You can safely skim say 10 thou off both lower and upper surfaces to clean them up a little and a decent (Cometic) gasket will seal the rest. That exhaust is a bit gnarly, but should be OK. I suppose you could have that welded up and then dress it back, but I doubt it is necessary. Even stock, they are not a perfect fit.

One might argue that the exhaust gasket (O ring) is not designed to take full on flame impingement, but I think you will be OK.

[Suzukidave]

I would say as long as the sealing areas around the bore , water jacket and transfer areas are clear of surface problems you would be ok to use as is . The exhaust port i would clean up a bit just so the carbon will not build up on the rough surface so fast and that could be done easy with a bir or sanding drum .