Honda Crf Has Gone Bang

[tootall]

Those exhaust valve seats are gonna want recutting at a minimum too.

did a proper job of it for a first engine blow up fella.

[Gix]

That motor was about 3 revoloutions from completly destroying itself.

Lack of oil? probably not. they don't hold a lot of oil anyway, so the lack oil in the site glass was due to it all blowing out the exhaust.

I'm going to disagree with Mille here and suggest that it was either piston skirt failure, or possibly big end. Either would allow the piston to hit the exhuast valves and bend them. The valves will open less if you lose the shims, but if you bend the valves they won't close fully causing the clearances to open up and allowing the shims to jump out.

These bikes are not designed for being held flat out on the roads for mile after mile, they are great fun when you do but there is a cost.

I'm guessing piston too.. I believe Daz( original owner) used a particular make of piston ( I think it was cosworth) and my guess is the piston has tilted then twatted the valves. Personally I think the head is scrap and you can pick em up cheap. But as has been said you are looking at around £900 to fix.

Crf has a 15hr service life on the rod but can easily do 50hrs or full season. I have built quite a few CRF motors for supermoto and once built are probably one of the best motors for road use but I would never use one on the road unless I knew it had been done.

If you really want a reliable crf for the road the 450x is the one to get as the gearbox ratios are far more roads orientated and most of the 'r' bits fit

[peter187]

On an MX bike we do a bottom end rebuild every 50 hours and a piston every 10-15. That's with mostly 2nd and 3rd gear riding. I don't know what the intervals would be if you're sitting near the redline in top for long periods on motorways and things, I'd suggest probably not very long at all.

[porter_jamie]

Smith brothers used them for mono racing and they were basically permanently inside the motor. And races only last 20 minutes.

[2T Institue]

Not much filtering down from MotoGP into a CRF then .......................? Your lucky you have the bottom end in tact usualy they put the rod through the cases.

[porter_jamie]

they are reliable. people think 2 strokes are unreliable, but they are not.

our rotax mono is reliable. we take it out after every race and check everything. it has a new rod and piston every season, a new 3rd gear twice a season and anything else whenever it needs it, absolutely regardless of cost. we run it in on the dyno and then take it out again to check the bore etc. if he misses a gear the motor comes out. we stick to a rigid warming up regime. oil gets changed every meeting. we check the afr every session. i stand at the side of the track and look for smoke on the downshifts. i listen at the pit wall to the sound and if anything sounds a bit odd the motor comes out. we monitor the oil temperature constantly (when the stupid logger works) basically you do anything you can to not the give motor an excuse to fail. i need to get better at recording the racing miles.

i think the hondas makes a good f450 (not that l like the f450, i think a 'proper' chassis is probably a better option) the standard parts are really cheap and you just wander into a dealer to get them.

[Superdunc]

Many of the replies suggest that the CRF would make a poor "moto450" - is this the case or can they be made reliable? Would something else be a better base for one, or are they not a great idea in reality?

Rich.

As Jamie says, they are fine as long as you maintain them accordingly, as as his schedule demonstrates, it's not cheap, even more so if you pay someone to do the work for you. The class seems like good cheap fun, but it really isn't.

The RRV450s which use the much maligned SXV motor, will do a full seasons racing and testing, they then go to an approved engine builder, at the end of the season for a rebuild which costs £1500.

However, the ECUs are set so they only rev to 10,500 rather than the 12,000rpm limit the supermot race bikes rev to probably reduces the peak power by 5-6bhp. This doesn't matter in a control formula, but if you were running in an open class you'd be running 12,000rpm, and tripling your rebuild costs.

[porter_jamie]

they use(d) the aprilia 450 v twin motors in moto450 racing when raced with Thundersport UK. I never saw one with a mechanical. And they rode them unbelievably hard.

[Superdunc]

Were the rrv450s based around the standard frame?

By the way, I'm more thinking for a toy for the road, rather than racing...

Yes they are. RS125 forks and brake, shorter rear shock and different linkage. Custom tank, subframe, rear sets and bodywork.

I know when I use my SXV on the road I invariably end up playing with sports bikes, and even on twisty roads I end up flatout for long periods of time. In some ways it's worse than racing them.

[peter187]

I'll just add in that if you are going to rebuild the bottom end of the CRF do not use a wiseco crank kit. They are total garbage. I've seen more than one fly apart with less than 5 hours on them and have heard reports of plenty more doing it.

[Chrisa112]

Back on topic...

That motor was about 3 revoloutions from completly destroying itself.

Lack of oil? probably not. they don't hold a lot of oil anyway, so the lack oil in the site glass was due to it all blowing out the exhaust.

I'm going to disagree with Mille here and suggest that it was either piston skirt failure, or possibly big end. Either would allow the piston to hit the exhuast valves and bend them. The valves will open less if you lose the shims, but if you bend the valves they won't close fully causing the clearances to open up and allowing the shims to jump out.

These bikes are not designed for being held flat out on the roads for mile after mile, they are great fun when you do but there is a cost.

Lucky it didnt destroy itself then haha. Good to know about the oil, was getting paranoid about it.

What do you mean by a big end failure? Not heard the term before :S

Yeah, I tried to keep it away from long straight roads but being in the south, thats pretty difficult!

I guess that holding them at constant revs is bad too (such as in slow moving traffic)?

I'm guessing piston too.. I believe Daz( original owner) used a particular make of piston ( I think it was cosworth) and my guess is the piston has tilted then twatted the valves. Personally I think the head is scrap and you can pick em up cheap. But as has been said you are looking at around £900 to fix.

Crf has a 15hr service life on the rod but can easily do 50hrs or full season. I have built quite a few CRF motors for supermoto and once built are probably one of the best motors for road use but I would never use one on the road unless I knew it had been done.

If you really want a reliable crf for the road the 450x is the one to get as the gearbox ratios are far more roads orientated and most of the 'r' bits fit

Indeed he did. It's a Cosworth piston.

I had seen people talk about the 450X engine (albeit briefly) and putting R components on it. Kinda just dismissed it though as I thought "Pffftt I've got the whole R engine, why would you even bother doing that..." Now I know haha.

Someone on here did recommend I change the sprocket sizes to get better gearing for the road.

I did wonder whether it was a piston or con rod bearing failure but the lack of damage to the inlet valves or evidence of any contact between them and the piston put me off that idea.

If the piston had been that out of control surely the inlet valves would have taken a hammering as well?

@Chrisa112 - was the motor still correctly timed up and the CCT working correctly? If the cam chain had skipped a few teeth you'd get what you've had happened....

Thinking about it logically I would have also thought that the intake valves would get damaged if the piston was changing angle inside in the barrel.

I dont know if it was correctly timed up or if the CCT was working correctly. Infact I cant even understand how the CCT works as its not like ones I've seen before. There's no spring or auto adjustment which makes me think its a manual one, but its not obvious to me how it adjusts either.

As I mentioned earlier, the cam chain did sound noticably more rattly from about 10 mins before it died, right up to when it died. My mate also suggested that the chain could have skipped a tooth...and that would make perfect sense (to me) with the damage the engine has. As you said, everything would be mistimed and start hitting each other.

On an MX bike we do a bottom end rebuild every 50 hours and a piston every 10-15. That's with mostly 2nd and 3rd gear riding. I don't know what the intervals would be if you're sitting near the redline in top for long periods on motorways and things, I'd suggest probably not very long at all.

I NEVER used it on the motorway! Even I knew that would be stupid/bad for the bike haha.

What you said about bottom and top end maintanence sounds more like what I had heard around.

Another question, hopefully not that stupid but the bike has a rev limiter, which I thought was to stop valve bouncing and over revving?

Cheers!

[Gix]

Crf R gearing for road should be 15/42

15t can be a struggle to get in but just grind off the little nobble on the swinger that holds the chain guide.

Its far better than going 14/38 as the chain will eat through the arm

I will argue the toss about wiseco cranks as I have used several including strokers without issue.Also used Falicon rods(farkin expensive)

Best aftermarket piston I have found is Vertex. I have heard of pistons 'rocking' with cosworths before and I did tell Daz prior to him building it.

FWIW once you have it rebuilt, never over rev a CRF, there is zero power in the last 7-800 revs so it is pointless and risky taking it there.

MY last 450x was more than a match for any R.

CRF's are one of the most reliable of the single 4t mxers and a well built one is a good choice for gp450/moto450.

Gearing is crucial so as not to rev it but also cam choice, carb set up and exhaust to keep the power in the mid range sweet spot with a decent top end.

Unfortunately, if they are not looked after they go bang big

[Chrisa112]

Cheers for the info Gix.

Deffo going to get this thing back up and running this year.

First question I have though, is it worth replacing the crank?

And if it not, is the best way of cleaning the crank/bottom end of metal shards and flakes just to strip it down and do each part indiviually?

[Gix]

You can do a rod kit but tbh speak with Mike Wright. Chances are he will have a full crank for similar money to a rod kit. I personally would do a crank. Be very careful removing the flywheel as you will see the crank has a soft end at the flywheel end. I've seen experienced Honda techs fuck a crank even using the correct puller, so put a socket over that

You will definately need to do the bottom end though.

There is also an oild reed valve between the cases that you will need to change out.

Best bet is strip it down and split the cases, then parts washer it and dry it off. Airline all the oilways. It will really need a complete strip but don't worry they are not complicated but oil pump timing and balancer shaft timing are crucial so get yourself a manual and be surprised by how clever you are.

Oil up all moving parts as you refit.

[Chrisa112]

After the initial thought of rebuilding...my mind is changing towards selling for parts/in current condition.

Offers? Haha.

[porter_jamie]

See my previous post

[Chrisa112]

See my previous post

Don't see an offer anywhere?

Only me saying I didn't want to sell it lol.

[porter_jamie]

How much? I don't know year etc..

[Chrisa112]

Pm'd