Help needed with my 1979 GS425e

[Guest]

I have had the bike for about 5 years. It has 30,000 kms. I maintain it myself. Valves done last year, was in good running shape. My daughter had been riding it this year. She is in Ottawa and we are near Toronto (about 4.5 hrs drive)
Last night my daughter called from the side of the highway. The bike had lost power, was leaking oil onto the right side cover, and had smoke coming from the right muffler and airbox.
A Harley rider stopped to help her. Determined there was no compression on left cylinder. She rode the bike 3 km to an exit. He later brought back a trailer and took the bike to his nearby house for safety.
So, She had ridden about a half hour in rush hour traffic and then onto a highway where she was riding about 7000rpm (130km/hr, and yes I have chastised her for riding that fast when she is a first year driver)

The bike has been leaking a bit of oil from the gearshaft seal which I was going to replace when she brings the bike home for the winter.

So, I have never got into the engine internals before. The bike is 37 yearss old. It sounds from what I read here that the head gasket is blown. My concern is what might cause that. Could the bike still run on one cylinder if the engine had eaten valves or lost a ring on the right cylinder. She said there was no weird noises when she started it and rode, but it did stall when she slowed down.

My concern is if something inside has broken I am probably not able to fix it myself.

Is there any chance it could just be the head gasket which I could replace myself? Anyone have any suggestions? The rest of the bike is in good shape, ie no rust, all original, tuned up, as I said was running well.

This is my wife's bike and fits her very nicely and is a good size for the riding we do. (My bike is off the road this year due to lack of funds).

[Brendan W]

Without seeing it's all guesswork but it could be the headgasket which is do-able. The absence of expensive noises or silences is encouraging. Any chance of a pic round the front of that pot when you get the chance.

[John Park]

The smoke from the air box is the major concern here. It could come from a totally blown head gasket which could allow some exhaust to pass into the cam chain tunnel and out the breather into the air box. This would also allow oil to be sucked into a cylinder and cause exhaust smoke.

The 400/425 head gaskets weren't wonderful, and the rubber seals on the cylinder studs would usually rot our pretty quickly. The engines also ran hot in comparison to the 450s which have considerably deeper finning. It isn't doing 7000rpm at 130K that will overheat it - although that's probably the practical limit, but idling in traffic, which is pretty deadly for any air cooled engine.

It isn't difficult to remove the cylinder head; just be forewarned about the exhaust bolts breaking off if they haven't been loosened for a long time. At 30k or 20k miles the rings should still be good; you can possibly get away with just a new head gasket. The tricky part is to get the head off without disturbing the cylinder block which can tear the base gasket thus requiring lifting the cylinders off the pistons. I don't know of a really good solution there other than maybe lashing it down really well with a rope over the cam chain tensioner; you can't wiggle the head side to side because of the locating dowels so you just have to pry gently.

Once it is apart the damage can be assessed. Even if it needs pistons or rings, it's still way easier than doing a Four. Finding parts could be difficult as they're pretty scarce for the old roller bearing twins. Try cmsnl.com . Modern Motorcycles in Vancouver may still have a few bits left; I gave them a valve cover gasket recently. There will be parts; somewhere…. eventually.

I have a soft spot for the 425, having done my best to wear one out. Failed, but fun trying.

[John Park]

On cmsnl.com the pistons are listed as unavailable, but the head gasket and its o ring are available at about 85 Euros. It's possible that the rings from a later 400 [GSX400] will fit as the diameter is the same - 67mm - but there could be differences. The cylinder base gasket is still available and inexpensive.

There's a set of cylinders and pistons that look functional on E bay for $150. Look under Suzuki GS 425 engine.

[Barneycanoe]

Thanks for the replies. I have the bike home and will get into it tonight. Apparently there was not a lot of smoke coming from the airbox, just a wisp and there was no oil there.

[Barneycanoe]

Bad news I'm afraid. Took the cam cover off and the plugs out and I can see there is a hole in the right piston. Thus is beyond my skills. I guess I will get a quote from a cycle salvage shop in Toronto but I think I may have to get another bike.

[Boba]

Bad news I'm afraid. Took the cam cover off and the plugs out and I can see there is a hole in the right piston. Thus is beyond my skills. I guess I will get a quote from a cycle salvage shop in Toronto but I think I may have to get another bike.

Noooooooooooooo...

what about grabbing a working engine off of ebay? Keep it alive! The engine from the 425 is very similar to the 400 from earlier models and the 450 from later models. The frame of the 425e might be a little softer than the 450 from later years, and the suspension is probably a little softer as well, but it will probably still work!

I'm pretty sure the carbs are the same as the 450 save the jetting.

All this to say, there is more than one motor that you could put into it, enabling you to shop around.

[geol]

The piston hole because your left carb holder is compromised and leaking cold air. The cold air tends to focus on the piston crown and will hole it if you are running at higher RPMs. Please don't ask me how I know this....

On eBay right now is a used set of pistons and a block. http://www.ebay.com/itm/1979-Suzuki-...p=mtr#shpCntId

To change the cylinder and pistons isn't a very difficult job and for about $300 (US) you can probably take care of this yourself with a service manual in hand.

[Barneycanoe]

I'm taking it to an old bike expert

The piston hole because your left carb holder is compromised and leaking cold air. The cold air tends to focus on the piston crown and will hole it if you are running at higher RPMs. Please don't ask me how I know this....

On eBay right now is a used set of pistons and a block. http://www.ebay.com/itm/1979-Suzuki-...p=mtr#shpCntId

To change the cylinder and pistons isn't a very difficult job and for about $300 (US) you can probably take care of this yourself with a service manual in hand.

Decided to take it to an engine rebuilder near me to see if he can sort it out.

Question though: My air cleaner filter disintegrated last year and so I replaced it with some similar foam. DO you think this could have anything to do with the problem? I checked it periodically and it looked fine, the piece I used had a very similar consistency to the original. Bike ran fine with it.

[Chuck78]

What ever came of this?

I know where you can get some stock bore forged high compression aftermarket pistons for the 425 (798cc GS750 pistons).
Also, a set of used standard bore GS850 pistons will bore 2mm oversized into the 425 cylinder, & rings are available. Wiseco GS750 844cc 10.25:1 pistons will also work, & Ape Race Products sell the pistons snd the aftermarket head gasket needed for this. Big Jay the owner is a forum member.

You will need to have the carbs re-jetted after a bigger bore piston set or higher compression piston set is installed, however.

[Barneycanoe]

Thanks, sorry for taking so long to respond. My mechanic says I need an entire engine, not just pistons so I am looking for one. Hope I can find one as bike is otherwise in really good shape.

Dave

[smilinbrad]

If you find a complete set up to fit could I buy your old carbs? I need the air screws and maybe even one of the bodys for my 425.
Thanks
Brad

[Chuck78]

Are the air screws really that hard to find? Are they different from the GS 450 carb air screws?

Most generic kits come with the air screws on carbs that I have worked on in the past.

To the original poster, a GS400 engine is nearly identical and you can bore 844cc Wiseco gs750 Pistons into it for 449 CC 10.5:1. A 77-78 GS400 engine is a direct bolt in. I even know where you can get some GS750 798cc high compression pistons to bore into the 400 cylinders to get the stock 423cc but in high compression form.

There was a 425 engine on ebay not too long ago.

What exactly was so wrong with the old engine that the mechanic told you that the entire thing needed replaced? Was the connecting rod damaged???

I'd just get a pair of stock bore pistons off of ebay from a GS850, bore the 425 cylinder out to suit, new 850 rings, and re-jet the carb accordingly using a WideBand o2 sensor and Air Fuel Ratio gauge.
Then have a valve job done and resurface the head, maybe the cylinders. Should run better than new. I can't see needing an entire new engine just because of a lean condition burning a hole in a piston. Have you questioned your engine rebuilder?

Aside from crank bearing replacement (press-pin type of roller crank needs to be taken to a shop generally speaking), rebuilding one of these engines is very simple. Just a bit time consuming. Camshaft timing is one of the few stumbling blocks where you really need to pay attention well to the manuals or else catastrophic things could happen.
Luckily the roller bearing cranks run practically forever as long as you don't run them out of oil. A friend of a friend had a surplus of gs550 engines, & decided to try to blow one up. He rode it to his buddy's house after draining all the oil out, then proceeded to rev the crap out of it and do fully pegged burnouts with the front brake locked for an unbelievably long time until the rings suffered heat seizure... once the overheated engine cooled off, it would crank over again and fired up, & they did even more burnouts...
Roller bearing crank, same as GS425...
My wife ran her GS550 out of oil multiple times and eventually the rings and cylinders were shot. It stalled out on the highway due to low comoression, but the roller bearing bottom kept going. That speaks volumes for how tough they are.

[smilinbrad]

The air screws for the 400 and 450 are mounted down in the top of the carb body. The 425 has the screws sticking out horizontally. Can't seem to find rebuild kits for the 425. Generics for the 400, 425, 450 that I don't feel have what I need although I may end up going that route just to find out. No longer available from Partzilla or Bike Bandit or Suzuki. Oh! the JOY of old, one year only stuff !!
Actually, I got the old screw out tonight. Shot it with PB Blaster for months. The bottom several threads on the screw brought a fair amount of carb body thread with it The top of the screw is toast as I had to turn it with Vise-Grips. Got the threads cleaned, a little oil and put it back in (needs O-rings). I'm not feeling all warm and fuzzy about it. I usually do better work than that

[Chuck78]

Please ask your mechanic the specifics of why you need an entire new engine, to help us help you out.
If you do really need one, I'm in central Ohio, & there are a few NorthEast Ohio members even closer to you in Toronto. Perhaps you could have one shipped to Ohio and drive down to pick it up if US to Canada shipping was too outrageous.

I have a running 425E still in the bike, and a seized (rusted rings from sitting) 425 junkyard spare but have race bike engine plans for both of them. I specifically was after 425's for the larger overbore capacity...