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 Post subject: Help for a young guy?
PostPosted: Sat Jan 20, 2018 8:58 pm 
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Joined: Sat Jan 20, 2018 8:29 pm
Posts: 27
Location: Ohio
Country: United States
Bikes owned: 77 GT250
Hello fellow 2 smokers! Been lurking a year or so but finally my turn to ask for help! Sorry for the incoming wall of text, but I'll try to keep it easy to read.

I purchased a 77 GT250 with 4500 Miles last February. It's cold in Ohio and wasn't ran much until probably May. The bike is stored outside under a cover.
After riding it a good bit I started noticing a knocking. It for sure sounds like it is coming from the bottom end. It ONLY happens when the bike is hot, and generally from 2500 to 3200 rpm when off throttle or holding it steady. It never does it under load. I started noticing the problem when slowing down to stop, Sounded like someone knocking on the side of the crankcase.

I tried to check if it was detonation. The bike had BE8S plugs in it when I got it, So I put the 9's in. No change. I tried high test gas, No change. I took off the stator cover and made sure everything was tight on that end and everything seemed ok. The sproket cover was absolutely packed in 40 years of old chain goo. Got all that cleaned out and made sure the chain had tension and everything.

Leads me to today. I finally got the bike torn down and the motor out and on the bench. Got the heads and jugs off. Pistons look fine, Some light scuffing but no deep gouges. Rings are nice and free and the cylinders were free of any gouges or lips. Top end looks fine. I did notice that the wrist pins were harder than I expected to remove from the piston. Is that normal?

There was no vertical play that I could tell in the pistons, just side to side. I never assumed there was an issue with the top end at all to begin with.

Now for the bottom end... There is 0 Vertical play that I can discern in the big end bearings. (There may still be some oil left keeping me from noticing any?) There is a good amount of side to side movement.

I was reading in my workshop manual and noticed they had a excerpt about discoloration of the flywheels, Well.... There is quite a bit to be honest. The outside flywheels have small amounts of oxidation. The middle ones look clean. Both have spots of discoloration, that match between both flywheels for each cylinder. See Pictures.

I did notice having to bleed the oil lines a time or two. I took the tank off to clean it at one point (Much later after I noticed the knocking). I bled the system as best I could and kept going. I resued the washers at the time which I wasn't really concerned with as the problem had been occurring for a good amount of time beforehand. I am wondering if the crankcase gasses were getting past the check valves. The left most side of the crankcase top had a little bit of oil pooled in it.

My main question is: Should I continue tearing down the motor to have the crank rebuilt? I would expect to see some amount of play in the big end bearings, but since I don't I am skeptical. I would hate to have the crank rebuilt and it not fix my issue. It is going to cost a few good bucks....

Here are some pictures
Engine https://imgur.com/IYkuorM" onclick="window.open(this.href);return false;
Combustion Chambers https://imgur.com/rleXHXJ" onclick="window.open(this.href);return false;
Cylinders w/ Pistons https://imgur.com/tP8Uo7S" onclick="window.open(this.href);return false;
Exhaust side of Pistons https://imgur.com/EuREmnJ" onclick="window.open(this.href);return false;
Intake side of Pistons https://imgur.com/lidazXn" onclick="window.open(this.href);return false;
Crank https://imgur.com/V05alA3" onclick="window.open(this.href);return false;
https://imgur.com/YDoaEUO" onclick="window.open(this.href);return false;
https://imgur.com/QWKE6u2" onclick="window.open(this.href);return false;
https://imgur.com/4hBMZ2q" onclick="window.open(this.href);return false;


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PostPosted: Sun Jan 21, 2018 5:38 am 
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Joined: Mon Dec 01, 2008 2:52 am
Posts: 1109
Location: Manchester, UK
Hi and welcome. First, that discoloration on the crank flywheels is entirely normal, so don't worry about that.

Maybe it's the pics, but those pistons look like they might have had a mild seizure in the past - measure them carefully and feel for scratches / scuffs on the pistons. Maybe they just need a clean. Check the cylinder walls for scratches & gouges, and measure the ring end gaps.

As for the knocking sound, make sure your exhaust pipes are clean inside and not blocked with carbon and oily crud. I had an infuriating knocking sound on my 380 for several months which sounded bad: it turned out to be a ring of carbon build-up in one of the exhausts that was causing a weird pressure-wave / knocking on a neutral or trailing throttle at 3,000rpm. Get one of those 'drain snake' metal springy drain cleaners and poke & prod up the exhausts every way you can. Also giving the silencers a good twatting with a rubber mallet (on the seams) can help dislodge crap too.

Some will tell you to tear the whole engine down now that it's out of the frame: I personally wouldn't, but that's because I'm lazy. If there is no measurable up & down or side-to-side play in the rod bearings, it's probably good. My 10 cents would be measure and check the cylinders and pistons, put it together with new wrist-pin bearings and gaskets and reinstall, and see how it goes.

Good luck.

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


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PostPosted: Sun Jan 21, 2018 8:51 am 
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Yeah Man, the Interstate

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 668
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
I agree with everything Craig said.
In addition;
I suggest you take some fine wet and dry paper to the skirts of pistons to take any high spots from the scoring.
I suggest you remove the exhaust baffles and remove carbon using a blow torch to burn it to a crisp then give it a whacking to knock off the burnt ash.
One of your pistons has a lot of black sooty carbon. Maybe the bike has been running rich on one cylinder. Get them balanced and make sure your air filter is clean.
And very importantly, make sure your oil lines and pump are bled through thoroughly and has no air bubbles.

I have one other question. Is there much wear in your bores? Could the sound be piston slap? Unlikely that this is your problem, but not impossible.


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PostPosted: Sun Jan 21, 2018 10:31 am 
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Joined: Sat Jan 20, 2018 8:29 pm
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Location: Ohio
Country: United States
Bikes owned: 77 GT250
Thank you everyone so much for your insight. Here are some more pictures that hopefully show the wear on the pistons and bore a little better. There is certainly some scuffing, But only one or two ridges that catch my nail. Bores feel relatively smooth and you can still see some cross hatching.

Here are the pics: https://imgur.com/a/JMxsR

Here is also a video showing the play in the big end bearings, What do you all think?: https://youtu.be/KnIMbxMfs58

Also notice the oil lines leaked over night :evil: :evil: I'll have to sort that out somehow.

Craig:"As for the knocking sound, make sure your exhaust pipes are clean inside and not blocked with carbon and oily crud." This could be highly likely! I did have the dreaded leaky petcock problem, and it was pouring out of the exhausts. I'll have to look into that. Thank you.

I have pulled out the baffles before and they never looked clogged, But there was hardly any wadding left. I'll definitely try cleaning them out with the drain snake and ill burn off the baffles. Used to work in a small engine shop and that was common to have to burn off spark arrestors on Sthil blowers.

Sporston: Carbon build up was definitely a little more on one piston, But it seemed odd to me that that piston came out of the cylinder with the cleaner combustion chamber. I'll for sure clean up the piston. The bike supposedly had the carbs done before I purchased it. It definitely ran great, but did have a bod at high load and low rpm. I'm fairly certain it wasn't piston slap or top end noise. It never did it at idle and never sounded like it was coming from the top end. Was much more of a deep knock as well.

Can the pistons be measures with a caliper? Or would that be too inaccurate for the shape of them? One measures 53.73 and the other is 53.75. Measured them right below the bottom ring.

And how hard should it be to get the wrist pins out? I always assumed they would slide right out but I had to knock them out. Not with a crazy amount of force. Just found a punch with a handle wide enough to catch the entire diameter of the pin and tapped it out.

Thank you all so much for your help! I really do appreciate it. What kind of sick bastard buys a 40 year old 2 stroke as their first bike? Hahahah


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PostPosted: Sun Jan 21, 2018 11:14 am 
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Joined: Mon Dec 01, 2008 2:52 am
Posts: 1109
Location: Manchester, UK
So it's an GT250A, with the extra transfer ports. Nice!

One of those pistons (and the corresponding cylinder) looks like it's ingested a bit of grit at some point. You could go over the scored parts GENTLY with some very fine wet&dry (800 grit), and then some metal polish and see how they turn out. The pistons in the 250A and B models are different to the pistons used in the earlier J/K/L/M models - they have the ring pegs in a different position because of the extra ports, so try and re-use the pistons you have.

To measure the pistons it's best to insert them in the bores and use a feeler gauge, like it says in the manual. Measure the ring gaps carefully too to make sure they are in spec.

From the video, the big-end bearings look fine. Wrist pins can be hard to remove, it's best to use a puller rather than knocking them out. Do replace the wrist pin bearings in any case, they cost peanuts, it really is NOT worth re-using them.

For the exhausts, I can't recall if the 250 has separate headers and mufflers, or if they're all one piece. If they are two pieces, you're laughing. Get your drain snake into both and make sure they're as crud-free as possible.

One thing - when reassembling and setting the ignition timing, USE A DIAL GAUGE. Do NOT refer to the so-called timing marks on the generator. The GT250A had quite a different timing setting compared to the earlier models, that was considerably retarded. But Suzuki did not always update the marks on the generator. Use a dial gauge and do it right (then scribe some reference marks on the generator so you can refer to them in future), or risk holes in your piston crowns.

Here are some resources that may help:
GT250A service supplement (details the differences from earlier models): http://www.oldjapanesebikes.com/mraxl_G ... /index.php" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
Loads of parts & service manuals: http://www.oldjapanesebikes.com/mraxl_G ... /index.php" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

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


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PostPosted: Sun Jan 21, 2018 11:59 am 
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Joined: Sat Jan 20, 2018 8:29 pm
Posts: 27
Location: Ohio
Country: United States
Bikes owned: 77 GT250
I was under the impression this is the "B". I thought it was a 77 but I suppose there is a chance it is a 76?

It definitely does look like it picked something up and sucked it through. Ill try that with the pistons to clean them up then do as the manual states about measuring them, Hopefully my feeler gauges are long enough or ill have to snag another set.

Glad to see that others agree that the big end bearings look good. Ill keep that in mind regarding the wrist pins. They were not horridly tight, But ill keep the puller idea in mind. As you say, No way I would reuse them. Ill go ahead and get rings, pins, and circlips on the way. As well as the gaskets.

My 250 has the long one piece exhausts with the removable baffle. Ill give the drain snake a try and hope to knock anything loose. Would it be normal that the knocking sound would only occur when the bike is hot if it was the exhausts causing a pulse wave like you described?

The timing is the most daunting thing for me as I am young and rather inexperienced when it comes to points ignition systems. Luckly I grew up in the age where absolutely anything was possible to figure out how to do with 20 minutes of browsing the web and youtube. I'll order a dial gauge as well so I can make sure the timing is right. I've got almost 3 months before spring so ill take my time.

Another question: Is there a safe ratio I can premix this without too much risk of carbon fouling just to supplement the oil injection system for piece of mind?


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PostPosted: Sun Jan 21, 2018 3:03 pm 
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Joined: Mon Dec 01, 2008 2:52 am
Posts: 1109
Location: Manchester, UK
It could be a B model, or an A. The engines were identical, the only difference was paint schemes and minor details in the chromework.

Be gentle with the pistons, they don't have to be perfect, just smooth off any sharp edges on the scrapes that you can snag your nail on.

The knocking sound only happened with my 380 at between 3,000 and 3,500 rpm when on a trailing (i.e. slowly closing) or shut throttle, and usually only when the engine was warmed up. I can't say for certain that you're experiencing the same issue, but it may help point you in the right direction. I would suspect a carbon build up where the header is welded to the muffler, i.e. right after the bend. That's where I would suggest focusing your effort.

Generally, if there was a problem with the crank bearings you'd hear it whether the engine was hot or cold.

Don't premix on one of these Suzukis, it doesn't really help as the crank bearings rely on the oil injection system working.

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


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PostPosted: Mon Jan 22, 2018 7:08 am 
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Joined: Sat Jan 20, 2018 8:29 pm
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Location: Ohio
Country: United States
Bikes owned: 77 GT250
Thank's again Craig. Ill get the pistons and ring gaps measured in the next day or two. I'll have go get the drain snake and play around in the exhausts. The problem you described sounds like what I was experiencing. I seem to remember mine doing it later on with the throttle open as well but that memory may be a little foggy. Since the big end bearings seem fine I can feel a little better knowing I didn't cause too much damage riding it around with the knocking. I just couldn't help myself.

I'm going to turn my attention to the oil lines now and figure out whatever I need to do with them. Is there something advisable to try and clean them in? I took them off the engine and sat them on the bench, and when I came out the next morning there were oil stains on the rag where it had leaked out of the banjos. Hopefully the valves are just gummed up and I can restore them to a working condition. Replacing that whole assembly seems fairly daunting.....

Thanks again so much for the help. I'll get that stuff measured and post back with it. I suspect everything will be in spec considering the low mileage on the machine. Everything under the clutch cover looks absolutely emasculate.


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PostPosted: Mon Jan 22, 2018 12:27 pm 
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Yeah Man, the Interstate

Joined: Wed Jul 10, 2013 12:04 pm
Posts: 668
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
one small thing. I forgot to mention; don't forget to clean your gasket surfaces thoroughly and remove all traces of old gasket and corrosion. While there didn't seem to be any evidence of a gasket leak, you don't want one in future.


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PostPosted: Mon Jan 22, 2018 1:01 pm 
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sportston wrote:
one small thing. I forgot to mention; don't forget to clean your gasket surfaces thoroughly and remove all traces of old gasket and corrosion. While there didn't seem to be any evidence of a gasket leak, you don't want one in future.


Will do for sure. Gonna take off the crankcase openings tonight and start cleaning everything up. The upper cylinder studs have corrosion for some reason so I'll clean those as well.

Just gotta figure out what to do about the oil lines.


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PostPosted: Mon Jan 22, 2018 9:59 pm 
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Sorry about the double post. I got the oil lines cleaned up and cleaned out. I think the check valves are faulty....

Hose assembly closest to stator side: Blowing through the banjo that goes to the oil pump, air comes out of the banjo that goes to the cylinder. No air will come out of the banjo going to the crank case. I can suck air from the banjo going to the oil pump. I can just barely blow through the banjo going to the cylinder. Can't do squat to the banjo that goes through the crank case.

Hose assembly closest to the clutch side: Exactly the same as above. Maybe I cant blow hard enough? Maybe it's the taste of carb cleaner getting to my head haha.

Is there something I can soak these puppies in? Any suggestions? I blew them out a bit with carb cleaner which got the old oil out. Maybe pack them full of it and let them sit?


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PostPosted: Tue Jan 23, 2018 4:46 am 
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Bikes owned: several gt250 ramairs
re: the oil lines - think about it logically. one side is just the same as the other. that would mean:
[1] both sides have exactly the same thing wrong with them [unlikely].
[2] there's nothing whatsoever wrong with them [probably].
i know the check valves do go wrong sometimes, but it's rare on low mileage engines.
connect the front banjos up and pump them full of 2 stroke from the oilpump end.
set your oilpump with the mark on the oilpump arm with the throttle dot in the carb and you should be fine.
make sure none of your nylon banjo washers are split - or get some new ones off fleabay
- 50 x m6 white nylon washers, about 99c :D
cheers, dd.

_________________
RGT250LC road registered. RG250 gamma engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.


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PostPosted: Tue Jan 23, 2018 7:14 am 
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dollydog wrote:
re: the oil lines - think about it logically. one side is just the same as the other. that would mean:
[1] both sides have exactly the same thing wrong with them [unlikely].
[2] there's nothing whatsoever wrong with them [probably].
i know the check valves do go wrong sometimes, but it's rare on low mileage engines.
connect the front banjos up and pump them full of 2 stroke from the oilpump end.
set your oilpump with the mark on the oilpump arm with the throttle dot in the carb and you should be fine.
make sure none of your nylon banjo washers are split - or get some new ones off fleabay
- 50 x m6 white nylon washers, about 99c :D
cheers, dd.


Yeah I didn't think about it till after I posted. I cleaned the old oil out with carb cleaner and it came out fine. So they may be ok. I ordered the Stat-o-seal washers from Mcmaster. Out with the old cruddy nylon washers.


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PostPosted: Thu Jan 25, 2018 7:26 am 
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Another double post....Sorry!

What's the best way to flush out any crud that may have made it's way down into the crankcase while cleaning up? Just wanna cover all my bases lol


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PostPosted: Thu Jan 25, 2018 2:39 pm 
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Bikes owned: several gt250 ramairs
there should be a fine threaded sump plug under each crank. it should be 14mm spanner to undo them. you won't undo the wrong bolts, because everything else [except gearbox sump plugs] is 10mm and 12mm :lol:
BUT - not all these gt250 engines have them. i've got some with and some without.
anyway, if you take those two plugs out, you should be able to squirt something up there to flush any crud out.
cheers, dd.

_________________
RGT250LC road registered. RG250 gamma engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.


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