Project Honda CB250RSD Project

Hi Fred,

thanks for offering a manifold, but one turned up a few weeks ago, so that's taken care of. Only item I still need to order is a new camchain, that's if no other funnies are found inside the engine itself. Spares for these bikes are not all that easy to find here, not many sold in the Netherlands. Someone offered me an engine minus cylinder head but now no longer answer phone or mail... Some spares in Germany once you know where to look but patience needed. OEM stuff is available but very pricy.

A 250 four might be fun to have but they are very rare in Europe and expensive, at least way over my budget. Mind you, I don't really want to see what this RS has cost me so far, and it's not even running yet. As feared and expected, a money pit but it keeps me off the streets.

In another thread I see you've got new job, newly engaged, new/another project bike in and a baby underway. All the best wishes for you & fiancée, but boy, are you going to be busy... enjoy!

 

Update!

News of little progress! The engine is now back in the frame but when doing up the bolts for the cylinder head cover it felt as if the threads were stripping, didn't dare doing them up to the full torque. Once I get round to actually starting it the whole thing may have to come off and out again to set helicoils all round. Now if only I had an M7 repair kit? Yes, there is M7 there, really, just like an old French car built to pre-WW2 standards but Honda must have had a better reason like better than M6 and no room for M8.

It also turns out the polish spare supplier sent me a nice drive chain kit for a nice price last August, but I never noticed untill January that they included a 46T rear sprockeet instead of the intended 44T, and now the chain was suddenly short of a few links. The (cheap) aftermarket front brake master from another supplier had the clamp threads factory mangled to save me the trouble of doing my own mangling.

So things are not going terribly fast and have now come to a full standstiil as we've sold the house unexpectedly quick and now need to pack stuff and all boxes seem to end up in the garage awaiting the move to the new place. This doesn't make for a nice place to mess about with bikes, look at it:



I mean, the bike looks better, but the only reason the bike is still visible is that I cannot lower it because of the muck underneath! No room to work on it.

So, give me a few months to move house and once I can find my tools again I'll be back here to tell you if the head came apart or not under load. That is assuming these guys in Poland send me a 44T sprocket and not another 46T... their service desk keeps on insisting I send back the 44T and they'll send me a 46T......oh well....

see you later, off to pack more stuff for moving to the new location!

 

Update !

Finally, finally, got some time left after all this moving house business and doing up the CX500 for this years tours (first one to the UK Cx club rally went well, thank you).

The RSD went on the table and the drip feed:



that's after replacing the ducktail which got crushed during the move, luck had it there was a usable one on this bay in the UK.

Opening the dripfeed tap resulted in the not totally unexpected mess, float valve stuck. The normal tap using the hammer handle didn't work of course. Now there was a way to get this carb out... reinvented that wheel... fixed stuck needle.. put carb back.

Even with the e-start living up to its reputation of difficult starting guess what, IT RUNS ! Nice steady idle, smooth, no rattles of any sort. Should not have them of course with new cam chain and balancer chain properly tensioned now, but even so nice to hear. Left it idling for a bit and it of course became f***ing hot, no airflow, I've been doing with watercooled engines of the CX type too long for my own good it appearently.

Still, it runs, sounds good even with the dodgy cylinder head. It is now cooling down, check valves etc later and if OK take out on the road, see what happens.

Even so, if anybody has a good cylinder head lying around? Yes, hen's teeth and all that

to be continued... at last !

 

minor news: it now has been on the road for the first time in years.

Dangerous stuff these test rides, even if like me you live in a 30 kmh (about 20 mph) village. Gave the engine a bit of throttle, and off we went. First defect found : forgot the mirrors, second very shortly after : front brake does not really brake... oops. Fitted a new master and a used CX500 caliper last year, was supposed to work, maybe I should have degreased the pads or something ? Guy in the opposing car had his brakes in good working order I'm happy to say and a good thing I live on the low end of the local hill

Also a bit of a nice surprise though, I'd forgotten just how light and nimble a bike this RS really can be. This is what I wanted the 250 single for, great! Just back from a 1K+ rainy trip on the fully loaded and fairing-ed CX500, very different ride to say the least. And yes, the carb still tends to flood, float valve needs a reminder what it's duties are.

(to be continued after bug fixing, safety testing will be included this time as well)

 

@Fred : thanks, let me know what happens with that head, actively searching for one here.

Progress report...... brakes fixed or at least better, mirrors found, real test run including motorway.
Result :

runs really well, but leaks between cylinder head and cover - as feared because of a PO partially stripping threads in bolt holes. Original rear shocks completely clapped out. Didn't let it go above about 110km/h for now. measured compression, about 11, fine with me.

Shall have to put a bit more tension in these bolts, see what happens. Putting helicoils in these deep holes is not easy and it really needs longer threads than a coil will provide.

Try again tomorrow, after that time for a bit of a holiday and the CB250RS is not coming anyway.

To be continued, much later probably.

 

@my67xr

Thanks for pointing out that longer inserts are available, obvious once you think about it but I never did. I think all threads are M6 except from one M7. Bit unusual that, looked like they wanted more than M6 but there wasn't enough "meat" for M8.

Another practical problem is that the holes are deep and some are blind, difficult to tap threads straight by hand, I don't have access to a machine shop. And there are holes acting as oil feed as well, don't want any chips in there while cutting...

@Jim (v50)

Do you run it with the leak or ever tried to stop it by applying a sealant on the outside. Not that I think that would work, but would be nice if it could be done.

In my case a previous owner put a helicoil in the front left hole, but it either pulled out or was never inserted correctly, because when i took the cover off the insert was protruding a bit above the mating surface of the cylinder head. Couldn't get the *!!@!@#! thing out so in the end used a mini grinder tool to cut to offending bit off. Other bolts just felt as if they can strip the thread any minute. First action for now has been a small prayer to the gods in charge of old and abused motorcycles, followed by pulling the bolts down a bit more. None came out, but that may change once I start it again.

But it'll have to wait, couple of weeks holiday first, and no need to hurry in any case. I now have 2 bikes that can be used and a maybe for the 250RS, and that's two and a half up on a few months ago

now off for a nice sunny weekend, hope you have one too,

Frans

 

So St Columbanus is our patron, didn't know, no wonder my bikes sometimes have weird problems !

But he must have been a good chap, Irish and multiplied bread and beer it seems! Petrol wasn't invented yet at that time I believe, but if he did beer mutiplication doing same for petrol should be easy. Some stories imply he had to leave Ireland because the ladies found him too attractive and that too fits the bikers (self)image!

Thanks for enlightening us Jim!

 

for now I haven't used the patron saints name in vain, and sure enough just tightening the bolts a bit didn't fix anything.

So the engine is out again, took cyl head cover off and noted 3 stripped threads (one should take an easy helicoil) and one bad helicoil (can replace I think). The two remaining are the deep holes next to the bearing behing the cam chain sprocket. Deep holes, too deep to tap (using available tools). Maybe there is enough left to use a threaded rod and a nut on top.

Any body got a recommendation for best sealant to use?

 

News !

Even I find it hard to take in, but it runs! The bl*sted cylinder head cover stayed in place and does not leak !
For those who cannot appreciate this achievement : out of the 13 bolts normally used to hold it down, a PO had mangled threads of 2, put a bad helicoil in 1 and left at least 2 feeling as if the threads might come out any minute now.

Solution : Clean and check mating surfaces very, very thoroughly. Remove helicoil, tap M8 (yes, original was m6 !), use two threaded rods in holes where original bolts wont fit anymore. Use small torque wrench to tighten all down in .2 kgm increments up to minumum spec op 1 kgm or as far as you dare. 8 Bolts came to full torque, rest at .6 Used Dirko HT sealant which has a good reputation for difficult cases. Allowed sealant to cure for 3 days.

The M8 is a kludge but it works, looks funny.



tapped M8 as deep as possible, selected an allen bolt from the "stores" tried it to see how far it woud go in, added copper rings to fill the gap under the bolt head (copper because they fitted) to avoid hitting EOH (end of hole) when torquing it down. Used the same torque as specified for the original M6, and behold, it works! This corner was an oily mess before but 20 km today and still dry.

No, it aint pretty but this bike isn't meant to win prizes. Don't know if I dare cutting off the excess sealant, and that's just the outside. Note : asking price last seen for an alledgedly good used engine here on Ebay was 600 Euro. Yes, ridiculous, but saw multiple ads looking to buy one...

Now the carb needs fixing, had to bend the float tab very far to get it to close the float valve, so it runs but fuel is way to low in the float bowl and lots of horses are still missing. Next step probably investing in a new float valve or preferably a known good carb. And the rubber of the accelerator pump is cracked, should replace that but might just seal it off. And the float bowl seal ring (original honda!) expanded and no longer fits, and..., and.... sigh.

All that assuming no silly hidden ignition issues or whatever of course. I will get round to that eventually, only been working on this for a year. Garage still needs new door and isolation so I can work in it next winter...

to be continued!

Ride safely, Frans