Maintaining a Honda GB250

[ZK-Awesome]

Righto so I got my first 250 (up from an A100) recently, a restored Honda GB250. When I say restored I say the frame, suspension, wheels etc have been done, but not the engine.

Carjam tells me the bike has approximately 90,000km.

As far as maintaining the bike, what should I be doing, and how many K's?

For example I just had the oil and filter changed, how often should I do this?

Bike shop did a compression check, it read 145psi but it should be 198psi, + or - 28. They suggested that doing the valve clearances may help this, otherwise the top end could be rebuilt. I suspect the valve clearances haven't been done in a long time, how often should these be done? Is there anything else that can be done apart from valves or new piston/rings to revive the compression? The engine still goes well, doesn't have any rattles or anything.

The speedo is also inaccurate - it is a Suzuki one. However even when not moving the speedo needle bounces around a bit- new cable needed, or would having a honda speedo fix it?

I intend to do a fair bit of riding during summer so I want it to be all sweet by then.

[ZK-Awesome]

Bump! 10chars

[CookMySock]

[trim] Carjam tells me the bike has approximately 90,000km. [....] Bike shop did a compression check, it read 145psi but it should be 198psi, + or - 28. They suggested that doing the valve clearances may help this, otherwise the top end could be rebuilt. [....] Is there anything else that can be done apart from valves or new piston/rings to revive the compression? Those kms are really high, and than means general wear and tear on the engine. If you want "ride everywhere" this summer, then really you are looking at doing a freshen up on that motor. At least rings and cylinder hone, and a valve grind. It might not be much more expensive to do piston/rings/rebore and bearings and seals, valve guides and seals, and then you have a near new engine.

Steve

[dogsnbikes]

Those kms are really high, and than means general wear and tear on the engine. If you want "ride everywhere" this summer, then really you are looking at doing a freshen up on that motor. At least rings and cylinder hone, and a valve grind. It might not be much more expensive to do piston/rings/rebore and bearings and seals, valve guides and seals, and then you have a near new engine.

Steve

What Steve said my speedo needle bounce and the odometer stopped working if your concerned about the speedo you have two options first find a replacement chances are it will be second hand unknown milage and condition may have same problem then you need to notify LTNZ on change of milage and reason but its all straight forward process

second option send speedo to Robinson's instruments in AKLD they will cheak it over and send it back like new...they did that too my CBX speedo cost was a $100 more than a second hand unit but they replaced cogs and I needed a trip rod and they reset the speed sensor light

but it all comes down too your buget etc

[Magua]

For example I just had the oil and filter changed, how often should I do this?



A safe bet would be to do it every 5,000km. Do you have a service manual?



Bike shop did a compression check, it read 145psi but it should be 198psi, + or - 28. They suggested that doing the valve clearances may help this, otherwise the top end could be rebuilt.

Do you have access to a compression tester? Get your valve clearances done (can you do them by yourself?) and see if it makes a difference to compression before you decide to do anything else. And I'd do valve clearances every 10,000km, or sooner if you think it's warranted.

[xwhatsit]

First of all I reckon you should grab a CBX250RS Haynes manual or an XR250 Haynes manual (I think the appropriate years would be 1984 on -- you need the RFVC engine). I don't think they made a GB250 manual, it was a Jap-only bike. That'll tell you how often to change the oil and things like tappet clearances for the valves.

90,000kms is a lot for these early XR250 engines. A lot of them are abused and go tits-up well before then. Like the earlier pre-RFVC engine, they (particularly the early RFVC engines) tended to crack cylinder heads, between a valve and the spark plug boss. That could be lowering compression too, perhaps.

On the other hand, if it's going fine, why bother? Unless it's particularly slow to the point it bothers you, or if it sounds like it's about to explode... is there any cause for concern? If it's low compression because the bore and rings are worn, then what's the worst that could happen, provided it's not burning shitloads of oil and you don't check the level.

[ZK-Awesome]

Thanks for the replies. I don't have access to a compression tester, however I think that doing the valve clearances might be a good starting point. I would be getting the bike shop to do them, so I could get them to do a compression test at the same time.

As for the speedometer, I have sourced a possible replacement. Do I really need to notify LTNZ? The last owner didn't, which explains the drop from ~70k to ~20k.

I have been told that these engines are quite hard on the ole oil as they run quite hot so it breaks down easily. xwhatsit how often do you change your RS's oil, and what oil do you use? There is a small oil leak out of the side bungs, but I also suspect that it is burning oil.

[CookMySock]

I think a compression test and a valve clearance check would be a good idea. Ask for a written evaluation/estimate of its internal condition, and ask for any suggestions to extend its' life, or refresh it's condition, along with quotes or esitmates to do said work.

But if you want to ride, ride, ride, all summer, I suggest you bite the bullet now and at least do rings, hone, and bearings and seals. Ask the shop about this.

You can save money by removing the engine and refitting it to the bike yourself. (not difficult)

Steve

[dogsnbikes]

As for the speedometer, I have sourced a possible replacement. Do I really need to notify LTNZ? The last owner didn't, which explains the drop from ~70k to ~20k.

.

you dont have too but it pays too as next time you get a WOF you may find that what ever is on your speedo now and what is on your new speedo are added as one and next thing you know your recorded milage is 145000 for example they askedme to send in a letter with the reading of the old speedo and the reading of the new speedo

[xwhatsit]

Thanks for the replies. I don't have access to a compression tester, however I think that doing the valve clearances might be a good starting point. I would be getting the bike shop to do them, so I could get them to do a compression test at the same time.

As for the speedometer, I have sourced a possible replacement. Do I really need to notify LTNZ? The last owner didn't, which explains the drop from ~70k to ~20k.

I have been told that these engines are quite hard on the ole oil as they run quite hot so it breaks down easily. xwhatsit how often do you change your RS's oil, and what oil do you use? There is a small oil leak out of the side bungs, but I also suspect that it is burning oil.
You don't need to tell LTNZ anything about the speedo (in fact I'm not sure what they'd do if you did tell them?). If it's jerking around it sounds more like the cable than anything else (unless it's a Smith's Chronometric speedo lol). I've changed speedo three times lol... having a bit of trouble working out if I've clocked 100,000kms on the old girl or not.

I suppose being an aircooled single it will run hot and cook the oil... also they don't have very big sumps, despite being a wet sump (did they make a dry-sump RFVC in 250 size?). I change my oil every 2000kms, but you probably don't need to do it so often as the RS is the more primitive pre-RFVC SOHC engine with no oil filter. Even so, oil is cheap, every 2000kms can't hurt, it only takes 10 minutes. What do people with oil filters do? Replace them every second change?

I usually use Caltex Delo 400 (it's either 10W-40 or 15W-40), it's a diesel mineral oil, supposedly quite good for old air-cooled lumps. Importantly it's cheap so I can afford to change it often... which is far more important apparently. Oil is like which deodorant you use, everybody's got their own favourite which they think does magical things... I would think your bike is of the age where mineral oil should be used in preference to synthetic (what year is it -- late 80s or a modern Jap import?) Which side-bungs is it leaking from? You mean the two little screw-looking things on the left side, one underneath each rocker box?

The DOHC RFVC engine uses bucket-and-shim, right? Do the cams have to come out? Might be an expensive service.

[lukejet]

Anyone know where i can get a head gasket for a Gb250? i've been looking for 6 months now and have had no luck...

L

[tychver]

Anyone know where i can get a head gasket for a Gb250? i've been looking for 6 months now and have had no luck...

L

GB250 was only ever officially sold new in Japan so you'll struggle to find that kinda stuff. Luckily a CBX250RS or XR250 84-85 gasket will work. I'm not sure about the XR250 86-90 gasket kits, they changed the engine again slightly and moved back to single carbs.