'Bout that time again! xr 250 top end rebuild

[waffles]

Some of you may remember that I rebuilt my bodged together xr250 over the summer, during its time with a previous owner it has sustained some serious damage and had been rather badly repaired. I rode it a couple of times and was out with some friends when they pointed out that it was churning out funky coloured smoke from the exhaust when I rolled off the gas. That, coupled with the fact that it was drinking oil like its going out of fashion, all pointed to the need for some investigation. I started this before Christmas and completely forgotten to post up here so I am going to copy across my rebuilt writeup!

27th November 2011

This is how the xr looked after its makeover in the summer....



Compression test was the first task, according to the Haynes manual compression for my bike should be between 180 and 191 psi and the xr was producing somewhere around 80. So here we go again, stripped down and back in the workshop for some engine tinkering.



The first thing to check over was the carb as it may have been tinkered with by the previous owner, the bike is running too rich so checking the settings would have been the logical place to start. Subframe had to be lifted up, wiring free'd up, cable ties cut and bolts out. Sadly I rounded one of the bolts holding the subframe in place so it needed some "persuasion", I need to add some of those onto my shopping list.



Taking the carb apart revealed there was some grit in there but nothing that would suggest the fuelling was set up incorrectly. Arse, time to tackle the engine it is then! I took off the exhaust (this needs repacking anyway) and headers which were starting to discolour where they bolt onto the engine. Another sign that all is not well and its running too hot.



This looked familiar, I got a lesson in how 4 stroke engines work by cranking the engine over and watching what happened. After finding all of the bolts (there are loads by the way, some of them are craftily hidden) off came the top of the engine. The plan was to strip the engine down to check out the barrel and piston.



Camshaft, just to the right of it is the camchain tensioner. The Haynes made it look very easy to remove using a high tech piece of equipment - the Honda opened-up-paperclip. Half an hour of struggling, head scratching and cursing later the executive decision was to leave the f*****g thing in place and carry on removing bits of engine. Clutch cover off with some difficulty as bolts were stuck and the gasket had welded everything together.



Im going to work on the clutch later as the bike has issues going from 1st to neutral when the bike is running.



By this point it was getting on a bit but may as well keep going and delve deeper. I pulled out the oil filter at the bottom of the engine and checked it over. Looked in good nick to me so I gave it a quick shake off and replaced. Time to go for broke and get to the piston. As the bolts came out they appeared to have baked on oil over them and they smelt like burnt chips.





Viola, it looks terrible! The smell was awful and there were chunks of oil sitting ontop of the piston. Turning the engine over so that the piston dropped back down revealed something interesting.



Around the side of the barrel is heavy corrosion and some pitting, pretty sure the engine has been drowned in a puddle at some point. Hopefully this is the cause of the poor compression and terrible oil comsumption!

The to-do list now stands at:
New subframe bolts
Rebore
Oversized piston
New gasket set
Inspect clutch plates
Repack exhaust
Stop fiddling with my bikes!

[waffles]

30th November

More bits fell off the bike today

This is the corrosion inside the barrel as a result of a dunking in some water.



I whipped the clutch basket off to get to the bottom of the camchain tensioner, more of that later. Off came the barrel with some careful thumping with a hammer and some wiggling of different engine bits. With a final tug the piston and barrel parted company and I could finally see the extent of the corrosion inside. Its fairly deep but will come out with a rebore. Go up 0.5mm or 1mm is my biggest decision. The fact that I can't seem to source a 1mm oversize piston unless I import from the states is a bit of a PITA. I'll keep looking!



Gratuitous engine gloamour-shot, its got no clothes on!



Here is the clutch basket, horribly discoloured on the outside and didn't fare much better on the inside.





Closeup showing pitting and wear marks. This will be buffed/polished out later and I wobn't bother replacing it. Its had a hard life but everything is well within limits according to the Haynes.







I have my shopping list, off to hammer the credit card into submission!

[waffles]

10th December

After a cruddy week at work it is again time to take out some aggression on an inanimate object, this time Mr Clutch Cover parted company with its gasket thanks to a razor blade. I gave it a bit of a clean up and it went into a bag ready to go back on once I have cleaned up the various clutch plates.



Ooh, shiny! Next up, the exhaust. I bought this from fleabay and it sounds pretty brutal. My bike became one of those antisocial bastards that I complain about. I could hear things rattling around in there! Time to bust out the drill and drill bits of various sizes. I read an article about how to do this in Ride, how hard could it be????



First few rivets came out with very little effort.



Two kept spinning round with the drill and they had to be chiselled off. The exhaust tip was stuck in place with silicone so I tapped all the way round with a hammer and chisel (gently!) and the end slid off finally. And with it came a small pile of carbon and the ends of the rivets.



Minging!



Apparently FMF pipes are ones that you have to dismantle at both ends before you can take the packing out. I didn't know this. Hence myself and 416cc spent 10 minutes with the molegrips trying to pull the middle section out of the exhaust.....



Drilled out two of the rivets at the other end, had to chisel off the other four. With the link pipe bend in the way this became pretty difficult to get a good purchase on the tiny rivet. Eventually they decided to part company and the exhaust finally came apart. "How hard could it be????" Bloody difficult apparently!





Hold your noses, here comes the old packing!



I left that outside to think about what it had done. Part of it was solid carbon, it stank and there were little balls of carbon rolling around in it that had caused the rattling I mentioned previously. I gave everything a good scrub with a wire brush but had to leave repacking it for another day as I don't have any replacement rivets of the correct size to hand. Time to tackle the cylinder and cylinder head instead. During the week I picked up a replacement cylinder, piston, gudgeon pin etc etc from taggkent . Putting my replacement piston and the OEM piston side by side it was clear that it wasn't an original one. I measured it up and I have managed to buy a .5mm oversize piston and rebored cylinder. Awesome! There is an uneven burn pattern on the dome of the piston though but im going to worry about that another day.



Some detective work later and the general consensus is that it is a Wiseco piston, here is a side by side comparison with an xr400 Wiseco.


But mine is definitely a higher compression piston, check out ma dome!



On to the cylinder head. First, screw the spark plug back in and pour white spirit in there to check for leaks.



Two valves were fine, no leaks at all. The other two showed small leaks. Time to pull the valves out then! Using a handy valve spring compression tool!



I pulled out the collets that held the valve springs and seals in place, made me jump as they make a loud pop when they loosen up. To keep track of what came out of where, heres the map what 416cc drew in his bestest biro. Under each valve is either a 1 or a 2 depending on where they came from, the top of each spring has red paint to make it easy to work out which way they go back on again.



Cylinder head minus valves



An inlet valve (left) and exhaust valve (right). Something looks odd here.



A little closer, this time. Both of the inlet valves are worn. Instead of showing a 45 degree angle they are more curved.



So I need to add a pair of inlet valves to my shopping list. List price of them is coming up at £18 each, fortunately the exhaust valves seem to be in the region of £30 each! Im shopping around to find some cheaper

Next up, probably the clutch. Stay tuned.

[waffles]

22nd December

Bits of the clutch are very worn and have deep grooves gouged in them so the plan was to put each part on the lathe and gradually smooth out the grooves. Which I did with some success.



Time to repack the exhaust, the packing needs to be wound fairly tightly around the exhaust core. Too tight restricts performance, too loose makes a noisy exhaust. The instructions said to hold it in place with some masking tape before putting the wrapped core carefully back in the outer case.



This is where it got tricky! The packing kept slipping and became a bit bunched up meaning that it had to be readjusted several times. Eventually I slapped some high temp exhaust sealant around the top and everything was hammered home. Brand new shiny rivets now hold everything in place. Thats one end done, going to do the other end another day.





RiDE guide = 10 minute job.
Actual time spent = A couple of hours so far.

[waffles]

1st January

Once again hit that "Urgh, is it ever going to get finished?" wall of frustration.

No pictures recently but some progress has been made. The exhaust is repacked and riveted back together waiting to bolt back on once the engine is rebuilt. I have a new set of Wiseco piston rings - I checked the end gap of the rings on my old piston and barrel and they were way way out. One had a gap that was nearly twice the maximum allowable amount (20 thou was the max wear and mine was 41 thou). The oil rings just fell straight through the barrel. Pretty sure they were borked!

Progress was temporarily halted with the hunt for a stone hone to bust glaze the new oversize barrel. Its a thirty second job but took a few days to actually get hold of one of these things. Just for giggles I ran it through the shagged barrel to see if I could take out some of the gouges and marks, several passes later and it made no difference whatsoever. Im going to hold on to the old barrel and get a 270 piston kit or something similar at a later date, that way I can prep everything while the bike is still running then spend as little time as possible swapping one barrel for the other.

I finished cleaning off all of the old gasket gunk from the gasket faces so they are all ready, cleaned the friction plates for the clutch basket and gave the cylinder and cylinder head a bath and scrub in engine cleaner. Fortuntely most of the carbon that covered the exhaust ports seems to have come off so no more chippping away with a knife and screwdriver for me! Apparently swearing at it or threatening to set it on fire is not the recommened way to de-coke parts of your engine

Still lots of little jobs to do before any parts of the engine can go back together. I have some pics to upload of previous work so I will sort that out later and edit appropriately.

[waffles]

1st January, later that day

First up, this is the stuff I used to reseal my exhaust. Halfrauds very own bestest brand exhaust gum, its insanely stick and sets fairly quickly so it needed a good smear before popping the end cap back in and lining up the rivet holes. Mmmmm



Finished exhaust with no rattles and lovely new packing. Although it doesn't say on the packet I would recommend using some goggles, a mask and gloves if you do this yourself as the packing material is made up of very fine fibres that are scratchy and easy to breathe in. But look how shiny my exhaust is! I wish I had weighed it before and after, im sure it is lighter though without the mass of carbon wedged in there.



Here is my cylinder head with modified inlets, Tim explained how creating that knife-edge allows the air to be split in two and flow more quickly to both of the valves allowing the engine to be a little more efficient. Filing down any bumps means that no turbulance is created so the air flows smoothly over the surface instead of swirling around creating eddies. Hey, every little bit helps right!



You can see it a little better here



So the lack of compression and huge consumption of oil has been traced to piston rings, damaged barrel, shagged valves and loose valve springs. Hopefully going to do a little more work on it tomorrow.

[waffles]

TODAY

Checking my clutch plates against a set of new clutch plates and its pretty obvious that mine are worn (although still within tolerances). New set ordered!



Its absolutely freezing today so I layer up with the thermals and set to work. Bike on ramp, posing for his photo session.



I have already cleaned, degreased, scrubbed and polished the cylinder and head so the first task is to clean up the gasket faces and peel off the remains of the old gasket set. I should point out that the bike has been in the garage and it went down to -5 last night and the engine block make my hands go numb instantly Blue roll it all of the hole just incase a stray bit of gasket burrows its way inside.





I checked the surfaces for any scratches or remaining bits of gasket and was pretty happy with it. Next up, laying out all the lovely bits to go back on. Mmmmm!



My new clutch plates soaking in oil



The cylinder and head get another scrub with engine degreaser then a dunk in hot soapy water, the barrel immediately needs a coat of oil when you do this as when it starts to dry it will corrode. Apparently I missed some when I did them last!



Im annoyed that this next picture wasn't in focus properly but I will post it anyway. After everything got a blast with the air compressor (and coat of oil if required) it was time to add bits to the engine again. Piston on, gudgeon pin back in with some light taps from a rubber mallet and then the circlips to hold it in place. Make sure the gap in the circlips is either at the top or bottom as if it faces to the side the movement of the piston (and centripedal force) can close the gap for you and make the circlip pop out while the engine is running. A thin smear of coppaslip on the new gasket and viola! Note - extremely shiny piston.



With the piston rings in place and the gaps lined up according to the Haynes manual, the cylinder could go back on. This is most definitely a two-person job as you need to gently slide the cylinder over the piston and squidge the rings so that everything fits in to the barrel. I trapped my finger in between the cylinder and the engine too



But there it is! My oversize piston and second-hand cylinder I am keeping the original so that I can do my quick swapover when I go for a big bore kit.



Time for some OCD and organisation. Inlet and exhaust valves, with springs and collets all labelled up (ta 416cc!). Head rebuild?





If you want to do this job yourself and get mildly annoyed by anything, walk away and get someone else to do it. Im a pretty patient person when it comes to things like this but it is massively fiddly and took two of us nearly half an hour to get the first valve back in. Valve guide seals in place, grease up the valve stem, pop it back in, put the springs in place, compress everything, grease up the collets, find a torch, get some tweezers, line up the collets with tweezers, gently undo the valve spring compresser, find the collet that pinged out, re compress, swear a lot, repeat.



HALF AN HOUR. I found the nack after that and each valve became easier to do, the final one took about five minutes or so and I only swore once!



And that is all that I had time for today. So I tucked up the bike for the night with a bit more engine than it started with.



Fingers crossed it will be ready to start next week.

[Boris]

Great write up. I'm looking forwards to the next instalment

[boboneleg]

Great write up Waffles, at the end of this you're going to have a bike that you can be confident in as you have done nearly everything to make it as good as new.

Well done

[416cc]

It's a good thing that the piccies came out well to illustrate how it came apart. This has helped in places, when the Haynes manual doesn't explain very well about where the locating dowels go back into place.

Good write-up. Takes ages to sort out all the piccies onto photobucket...