CBF250 Engine Problem - Part #2 - Planning the fix

The damage to my CBF 250's engine seems fixable at a reasonable cost.
 

I was keen to attempt a repair because the engine is in surprisingly good condition for a 250cc that has done 65,000 miles. Remember that at its normal cruising speed it's spinning at 7,000 rpm. 

The parts - two inlet valves, cylinder head gasket, valve stem oil seals x4, exhaust gasket.

The oil seals aren’t essential but it seems a good idea to replace these while the bike is apart. They are very cheap items. The CBF's oil consumption has increased recently and it's likely that oil is being lost through these seals. As it turns out it looks to me that the old seals are worn (the hole is bigger) Remember that the valves have moved up and down inside that seal 300 million times (give or take) 

valve guide oil seals - old & new

Also I have to repair or replace the tensioner. The spring is not available as a spare - it comes as part of the tensioner unit. The cost isn't prohibitive but I didn't feel like giving Honda the cash for the unit that had failed and caused the problem. Luckily a search on eBay came up with a solution - a manual tensioner. This is just a plate with a bolt & lock nut. You set the tension manually. There is nothing to fail. I was surprised that this was available for the CBF, these are usually fitted to competition machines but I realised that the CBF's engine was similar to the enduro XR250.

Tensioner old & new

Tensioner fitted

Also I need stick with suckers on the ends……see next instalment

CBF250 Engine Problem - Part #1 - What went wrong

My Honda CBF250 has been going very well but a few weeks ago that changed.

On a visit to my local Aldi supermarket for some essentials (a cordless drill & a six pack of Stella Artois) the bike suddenly started making a knocking noise and vibration increased. I made it home but realised that something serious was wrong. 
   

I turned the engine over by hand and there was a loud clicking noise and no compression - yikes! I removed the cam cover and the problem became obvious. The cam chain was skipping over the cam sprockets and the cams weren't turning. I removed the cams but there was no signs of seizure. Because the chain seemed loose I removed the cam chain tensioner and found the source of the problem. The tensioner wasn't tensioning.  
 

This ain't right

The tensioner with broken spring. The spring seemed pretty thin - like a razor blade. My micrometer says 0.15mm, which seems pretty skinny to me.

The tensioner has a spiral spring (like a clock) that pushes a plunger against a blade. I stripped the tensioner and found that the end of the spring had snapped off. Slack in the chain had allowed the cam timing to go out. When the engine is running the valves go in and out and the piston goes up and down. They use the same space but at different times. When the timing when out they hit each other hence the noise and vibration.

I removed the cylinder head to establish the damage. The two inlet valves were bent. Luckily everything else seemed ok.  
 

The valves weren't seating properly

I don't have a valve spring compressor so I made a tool and used my vertical drill.

Bent

The head is fine

Once cleaned up the piston looked ok

I wasn't unhappy about the failure. The CBF has done a lot of miles for a 250 (65,000 miles) and works hard. But I have to make a hard-headed decision. The bike isn't worth much so it's not worth spending too much on it. It looked like a pair of valves and a head gasket would do it so a repair seems worthwhile.

The CBF is quite a simple engine and access is good so it's not hard to strip down.

To be continued.......

A Sad Sight

The weatherman said it would be hot today (well, hot by British standards) so I headed to the Pennine Hills.

Between Penrith and Alston I stopped at the ruins of the Hartside Top Café. This was a famous bikers' café that was destroyed by fire earlier this year. 

 

The view looking west towards the Lake District.

In Brampton I saw this horse-drawn caravan. I had a chat with the owner. He was touring the country at 8 - 10 miles per day! He said that they'd done 12 miles that day and had set off at 5:30am to spare the horse from the heat.

Country scene

Crucified moles - why?

Completing my Coastal Journey

Last winter I took some runs to the Lothian coast - from west of Edinburgh to Dunbar. I thought I'd continue this coastal run through the Scottish Borders.

 

A period of fine weather here continues but it was more cloudy at the coast, but this gives some dramatic skies.

 

My first stop is at White Sands just south of Dunbar where some intrepid children where braving the North Sea.

The small ex-fishing village of Cove which overlooks this impressive…eh…cove.

This monument commemorates fishermen from the village that died in the storm of 1881 and depicts women and children looking out to sea.

Pease Bay. It's always fun crossing a ford on a bike. There's been a dry spell so I guess this is as low at it will get.

The coast road

The next fishing village - St Abbs.

My final stop was at the fishing port of Eyemouth.

This fine mansion overlooks the town. Built in 1753 by a local smuggler, John Nisbet. Smuggling must have been a lucrative business and the house is said to have many secret places for the contraband to be stashed.

In the ground of the mansion is "Nisbet's Castle". Actually a dovecot that has been converted into holiday accommodation.

They take fish seriously here. Each year a "Herring Queen" is chosen and past Queens were displayed in the town.

I'm not happy about this. A pub called "The Contented Sole" I get the joke but puns should be reserved for hairdressers etc, drinking is a serious buisness

The Heap Ain't Getting any Smaller….

I've enjoyed riding my re-activated FJ1200 over the last 6 weeks but have had to deal with one issue of owning a heavy, powerful bike - they eat tyres. I had a pair delivered this afternoon and fitted the rear.

When you run three bikes, do a fair mileage and fit your own tyres you have the problem of disposal. I have an impressive pile of dead tyres at the bottom of my garden. My local coup (rubbish dump) wouldn't take them in the past but now do but charge £3 a tyre. 

Featured Bike - Honda CRF450L (2019)

This recently announced bike has generated much excitement in the dirt bike community. It's a trail bike (dual sport to you Americans), a street-legal version of Honda's CRF450X motocrosser and CRF450R enduro. The bike seems to promise serious off-road performance and road bike versatility. The new Honda will challenge Suzuki's long-running DRZ400 and Euro exotica like the KTM EXC500-F. 

Honda CRF 450L

But enthusiasm for the bike diminished when its details became known. Firstly the power was quoted as 25bhp. Unbelievable since the bike's competition cousins put out 50+ bhp and the DRZ 39bhp. This figure seems to be an error by Honda Europe who mixed the bike up with the CRF250L. The real figure is likely to be in the 40's.

Suzuki DRZ400

Secondly the CRF's service intervals are distinctly competition bike - 600 mile oil changes and 1,800 mile for valve checks. The kicker was a scheduled engine overhaul at 20,000 miles. Again these figures are unbelievable for a dual purpose bike. The DRZ's intervals are 4,000 miles for oil & 15,000 for valves - the same as my SV650. The Honda's intervals only make sense if the rider was doing hard dirt riding only. Riders nowadays expect never to overhaul a modern bike engine. My CBF250 works pretty hard and had done 65,000 miles without an overhaul. 

KTM EXC500-F

Lastly, this competition heritage doesn't come cheap. Price in the US is nearly $11,000 - 50% more than the DRZ or Honda's own XR650L and about the same as the Honda VFR800 (Interceptor in the US)

There is no indication (that I can find) that the bike will be available on the UK market and at a likely £10,000 here it is not going to be a big seller. Still I'm interested in reading the reviews. 

As far as dirt bikes are concerned a favourite of mine was the Honda NC400 Falcon - never on the market here but a type of bike they just don't make anymore - and old fashioned trail bike.

Honda NX400 Falcon

Back on the FJ and a Simple Repair

If you follow my blog you'll see that I've been riding my Yamaha FJ1200 over the last month. The bike was unused since autumn 2016 but is going very well. I did about 1,900 mile on it in June and it was great to get the old thunderer back on the road.

I've done a little maintenance. I changed the engine oil & filter, checked the valve clearances (all ok) and put in new spark plugs.

There was one slight repair I did. The rubber tubes from the airbox to the carburettors had split. Luckily the ones on my old FJ (now a "donor bike") were ok so I swapped them.  
  
 

Both outer rubber tubes were split. This didn't effect running but would tend to make the bike run weak.

The airbox off my old FJ. Its tubes were in perfect condition. I soaked them in silicone lubricant for a week to make sure that they stayed pilable.

All back together

The bike has a K&N washable air filter. This is a great product but the 50-100,000 mile service interval is wildly optimistic.

Mine was pretty filthy after 7,000 miles. Restoration is simple (see here)

My old FJ selflessly donated parts to keep the new bike going.