Cafe Racer Forum banner

61 - 70 of 70 Posts

·
Registered
Joined
·
44 Posts
Discussion Starter #61
A few weekends of activity and I'm just about ready to put the engine back together......

Head, cylinder and block have all been cleaned and taped off.....

103692


103694


Then primed and painted

103695
103696


103697


103698


103699


The engine fins are perfectly polished, but they've come up ok.......

And the tank was stripped of paint (what a fuken shit job that is.....)



Bogged where the tank was dinted.....

103701


And Primed.......ready for lovely Honda Red to go on......

103702


My panel beating skills arent the best either, so the bog finish is not perfect, with a few wobbles here and there, but it'll do this bush mechanic.

I've checked the ring gap on the OLD TOP RING and it's showing spec 0.012" at the top of the cylinder, but I understand they should be checked at the BASE of the cylinder?

Either way, I'll replace the existing set with new, and see how we go.......hope I don't fuck up setting the ring gap,never done that before.......

I'm also considering replacing the timing chain while I've got the side off.......but not sure if the position of the cam chain tensioner warrants it? See below from when I pulled the top off originally......Any thoughts are appreciated?

103703


Soooo, we're making good progress......now comes the tricky bit.....putting it all back together! haha
 

·
Registered
Joined
·
6,361 Posts
Does the cam chain have a plastic guide ?
I think you will find that to be the part that wears out before chain stretch necessitates replacement.
 

·
Registered
Joined
·
44 Posts
Discussion Starter #63
Does the cam chain have a plastic guide ?
I think you will find that to be the part that wears out before chain stretch necessitates replacement.
Hi Trials Rider,

yeah it does...... but that doesn't look to be too worn....... side walls are only a couple mm high, so it doesn't look like too much of the plastic has been removed......

I'll read up on it some more, thanks mate.....(y)
 

·
Registered
Joined
·
274 Posts
I've built a lot of the larger RFVC motors but never a 250 so not sure if this is relevant or not but thought I'd mention it anyway! On those the cam sprocket on the crank is not symmetrical (the teeth aren't quite central to the boss) and can easily be fitted onto the splines the wrong way round....moving the cam chain a mm or 2 closer to the crankcase....often enough for the side plates to just touch it....and make a new cam chain sound very old!
103706
 

·
Registered
Joined
·
44 Posts
Discussion Starter #65
I've built a lot of the larger RFVC motors but never a 250 so not sure if this is relevant or not but thought I'd mention it anyway! On those the cam sprocket on the crank is not symmetrical (the teeth aren't quite central to the boss) and can easily be fitted onto the splines the wrong way round....moving the cam chain a mm or 2 closer to the crankcase....often enough for the side plates to just touch it....and make a new cam chain sound very old!
Thanks UncleRob.....Not sure.... I'll take a look at it from my end and see if I can see what you're talking about.......
 

·
Registered
Joined
·
44 Posts
Discussion Starter #66
Continued Progress.....

1. The donk is going back together.....

Strangely, the NEW Wiseco rings seem to have a Gap slightly wider than spec.....without any filing.

I guess that would normally indicate that the Cylinder is over the 77mm size of the Piston.....BUT - the existing (old) rings seemed to be closer to Spec (.012") than the new rings, so I'm guessing it's not the cylinder.....either way they've been installed and the Cylinder and Head are back on.....

103789


And the timing cam and chain are back in.....but I seem to be missing the locating lugs which sit at either end of the cam, just beside each bearing......not sure where they disappeared to, so will need to get two more before the Cover goes back on and I can put it back in the bike......

The Tank has come up pretty nice.....

103790


I gave it four coats of clear over the weekend so it's ready to go....

And I started trueing the wheels......Front Wheel was the first attempt and it also came up pretty good....I wish I took a before vid because that rim was wobbling like a piece of spaghetti before I started.....Need to go round and tighten all evenly now, but hopefully she's good enough.

(How good is the footy in the background...... :)

Rear wheel is next.....I THINK the offset on these rims is about 20mm......wish me luck. ;)
 

·
Registered
Joined
·
44 Posts
Discussion Starter #67
Teaser Time......here's the progress so far....
103919


103920


Engine is all back together, in the bike and just needs Valve Clearances set.....QUESTION & CLARIFICATION PLEASE - I backed the valves right off when installing the top cover so I need to re-set completely. My understanding is that TDC on the Compression Stroke all CAM Lobes will be facing DOWN and all "Tappet" faces as high up as they can go, whereas on TDC on the Exhaust Stroke the two exhaust tappets should have lowered. Rotate another 360 degrees / stroke from there and we should be good. Is the above the best way to confirm Compression TDC when setting Valve Clearances from scratch? Or is there an easier way? Thanks in advance.....

Tyres are Pirelli Scorpion MT90 AT's, which have that more aggressive tread pattern I was looking for. I like em.

RHK Gold Chain matches the bars nicely.....and basically everything is coming up pretty well, particularly the black painted bits, even with the DIY flavour. I'm considering leaving the Brat Seat loop as is, sans rear fender, but will assess as we get closer to the finish line.....easy add/remove one way or the other....

Carby Rebuild is next - I'm hoping the old OEM Keihin Carb will do the job......(Was considering just swapping it out for a new Mikuni, but that would've just been taking the easy way out.....at least I'll learn about Carb's doing the rebuild). ANOTHER Question - Does anyone have a good recommendation for Jetting the stock Keihin Carb for a XR520 with a 77mm Piston (is that a 280 kit???)....thanks in advance.

Once the Carb is rebuilt and tarted up (probably just black paint but maybe some polished bits) that'll go back on then it's Electrics (scary) and cables, tank and set and we'll see if she fires up hey? (Pray to the DIY Workshop Gods for me....)
 

·
Registered
Joined
·
6,361 Posts
(y) Watch for the intake valves to just finish closing at the bottom of a stroke,
now as the piston rises we are for sure on our way to compression TDC.


Use a micrometer on your feeler gauges to get a feel for how snug the gauge should feel between the valve stem and the adjuster :geek: kind of like a practicing dry run.


The valve adjuster likely has a square head to turn it. That square is the same size as a (red) Robertson screw head. You can make an adjusting tool out of a short stick of wood with a Robertson screw threaded into one end of it.
 

·
Registered
Joined
·
44 Posts
Discussion Starter #69
(y) Watch for the intake valves to just finish closing at the bottom of a stroke,
now as the piston rises we are for sure on our way to compression TDC.


Use a micrometer on your feeler gauges to get a feel for how snug the gauge should feel between the valve stem and the adjuster :geek: kind of like a practicing dry run.


The valve adjuster likely has a square head to turn it. That square is the same size as a (red) Robertson screw head. You can make an adjusting tool out of a short stick of wood with a Robertson screw threaded into one end of it.
Thanks TrialsRider,

I assume though, that as the valves have been backed all the way off, I'll need to watch for the intake tappet assembly instead?

The micrometer tip is a good one, thanks.

The adjustment on mine is a simple flat screwdriver with double lock nuts.....so I'm not 100% sure if we're talking about the same thing there......def not Robertson screw....?
 

·
Registered
Joined
·
6,361 Posts
Adjusters must be a little different then mine (y) principle is the same,
Honda trials bike engines also have roller bearing rockers and the cam rides on a roller bearing.
 
61 - 70 of 70 Posts
Top