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Rebuilding 1979 Suzuki GS750 engine

  • Thread starter Thread starter DaveInTexas
  • Start date Start date
D

DaveInTexas

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Hello folks, my first post - glad to find this forum.
I have been looking for a project bike lately and found the one listed above for $300. I have some experience working with small engines of many types, and aircraft engine overhaul, and own & maintain a 1970 Honda CB750....& I own adequate toolage.

The bike I found is reported to have low compressions.
Before I buy it, I wanted to find out if it was still possible to get parts to rebuild this engine ie pistons, oversize rings, valves, bearings etc.
Where can these be found? Any suggestions on an all-up price to do an overhaul at home?
Rough ideas I have right now (please throw out corrections) is that this bike, after overhaul of the engine and any repairs of the bike will be worth on average, $1000-2000 depending on miles, condition of many things on the bike...but on average. And, would an engine overhaul be about 1000$?
I am not going to make money on this but I wanted to get an idea of what a fair price is for this bike considering all that must be done to it.​
 
You can get anything, it's not that expensive, Suzuki still carries most parts,

BUT !!!

Low compression on a poorly maintained GS is almost always caused by valve clearances being too tight. They tend to get tighter and toghter as the engine wears, there can be no compression if the valves aren't closing. I have resurrected many many "dead" Suzuki engines by adjusting the valves, and doing some other routine maintenance.

Check it before you tear it all down.
 
Great tip, thank you.

Where would I buy engine parts if it comes to that?
A link would be helpful, googling like crazy but no luck!
 
Google "suzuki motorcycle parts", you will find tons of companies selling OEM Suzuki parts.

Rings, OEM Suzuki gaskets, and valve stem seals is all you should need unless the engine has burned a bunch of valves or has more than 100k miles.
 
Google "suzuki motorcycle parts", you will find tons of companies selling OEM Suzuki parts
Click to expand...

A link would be helpful, googling like crazy but no luck!
Click to expand...



I have been googling. And I do find tons of companies selling OEM Suzuki parts....but so far no 1979 GS750 engine parts like the ones listed. Thanks for any leads.
 
I'd recommend you stay away from G&S Suzuki. They are, in fact, the cheapest, but you will have issues with them.

The general consensus/recommendation of the forum is to use Parts Outlaw, but there are many others. BikeBandit tends to be pretty expensive. I switched to PartsOutlaw after having problems with G&S.
http://www.partsoutlaw.com/
 
The bottom end bearings on a 78 GS750 are roller bearings and almost never fail. Top ends, unless you're talking really high mileage, are usually in good condition as well. Don't sweat the low compression until you've verified everything. Do the maintenance that's probably not been done for 30 years. You may be surprised to find that the engine is in much better shape then you think. Here's my suggestion.

Start with a good valve adjustment. Most cases of low compression are simply tight valves.

Change all your fluids. Change the oil and the filter. Don't forget your brakes. Change all your brake fluids out and clean the system.

Do a compression test. This should be done only AFTER you've adjusted the valves and not until then. Do this with the throttle wide open. A lot of misdiagnosed compression issues are because they didn't do the compression test correctly. Expect the compression to be around the 120 mark if the engine is cold. Best to do the compression test when warm but if she's not in good running condition then a cold test will give you an idea of her condition. Even if it's low you may find that, after she's been ridden a few hundred miles, the compression numbers will come up.

Rebuild the carbs. Do a proper carb cleaning. Not just a spray here or there with carb cleaner. You want to disassemble and dip the carbs completely. Poke through every hole and jet and spray cleaner in and out each passage. Here's a rebuild tutorial that will help: VM carb rebuild tutorial.

These are tough little machines and will take a lot of abuse.

Here's a link to BikeCliff's website that has a ton of information as well:

BikeCliff's Site

For OEM parts I've been using PartsOutlaw.com. There are many others but they seem to have good prices and have been reliable.

For some aftermarket parts you can find them at Z1enterprises.com


Welcome to the site and here's a link for that: GSR Welcome!
 
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Great choice in projects! The GS750 was the fastest and best handling 750 of the 1970's. the engines are very tough, and the stock camshafts have quite an aggressive profile and bark to them... The frames are better handling than any other big 4 japanese manufacturer's.they are lighter and better handling than a Kawasaki kz1000, and almost as fast in a quarter mile, I believe two tenths of a second and 3 mph slower (lighter bike). The kz fetches in much higher price tag in stock form and gets a few mpg better.

the downsides - although the bottom end is nearly indestructable, the massive crankshaft and kickstarter assembly make the 750 engine weigh 15lbs more than the gs1000, and these engines are fairly wide - DO NOT lower the bike much & epect to be leaning in hard into corners.

easy to fix flaws:
*it has a permanent magnet alternator, which is a plus, but the rest of the charging system was a flawed design. Ditch the regulator rectifier - especially if it's still the stock unit, sometimes on older models it is two separate units. after testing your stator output & checking the ohms resistance across the legs as outlined in the stator papers link on the GSR main page, Install a Shindengen SH-775 series style r-r (search here for the polaris rzr 800 oem part # that will allow you to find them on ebay or a polaris/can-am/seadoo dealer) or the CompuFire series style unit that cost much more but is as good as it gets.

*after the r-r upgrade, your engine and charging system will run much cooler, and you can get rid of that wiring loop that sends 1 of 3 stator output wires to the headlight switch and then back down to the regulator rectifier. this was to lessen the stator's load and heat output when the headlight was not being used and not drawing massive electric current from the charging system. the switch and wiring connections get dirty and will cause major headaches.

*the stock springs on most of Japanese bikes we're incredibly weak from the factory. Look into an $80 set of aftermarket Sonic/Progressive/RaceTech fork springs, or else research of chopping your stock spring to get closer to aftermarket rates and better handling. I got mine to .85kg/mm, .90 or 1.0 was what I would've gotten aftermarket.

*upgrade rear shocks, try to budget $200 for some hagon or progressives if you can. More modern technology will cost you at least double the purchase price of the bike (yss z-362, works perf., etc), but will be worth it if you really appreciate a better handling/cornering machine.



Follow the advice of forum members here on maintenance issues (there is a wealth of knowledge amongst us), and download the factory service manual from BikeCliff's site.
As stated, dismantle &dip the carbs, buy an oring kit from cycleorings.com as well as intake boot orings, & rebuild the carbs properly. Check out all bearings, chain/sprocket wear, fork seals, brakes, etc. Lastly, put a great set of tires on it to drastically improve the handling over 30 year old tires or cheap replacements. I LOVE the Shinko 230's, and they're CHEAP! Avon AM26's if you put a lot of highway miles (or straight roads, rather) on them still want an excellent handling tire.


there are tons of other mods you can do to them, Wiseco makes a very nice big bore kit for them also!you can upgrade to late model ninja and CBR brake parts if you search twin pot mod on this forum. lots of other GS models have compatible parts that you can upgrade yours with as well.

Best of luck.
 
Welcome to the forum Dave. I see you are in Texas. If you are in the Dallas Fort Worth area and need a hand with anything let me know.
 
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