84 Honda CR 250 Modifications

[Kenneth S (222)]

Thanks guys for all your comments.  I have a new barrel but it requires a rebore and a new top end...$400, when I have only recently spent that on the current barrel. The course of action I have decided to take is rule out the cheap fixes first. The mechanical seal was suspect so I have rebuilt that whole system with all new seals. If it was slowly leaking coolant into the clutch cover it won't now. I have also changed coolant to a blue motorcycle coolant so I rule out the coolant and see a colour change in the oil if it does leak into the gear box, replaced all the tired head studs with brand new Honda studs and after Cooch's very interesting comment, I might go half way and put some teflon washers on each end of the head brace. Don't like the idea of racing a 30 year old motocross frame without all its bracing!

Thanks to Hardo and Nathan for the blasting.

Thanks Alex for the diagram, I followed all your measurements with my Dremel. The case looks better in the flesh than it does in the photo.

Fingers crossed!

[evo550]

There are plenty of head stays left off old bikes because of the issues they cause to heads and cylinders with frame flex, it's an idea worth serious consideration.

[crs-and-rms]

looks great glad to help

[GMC]

Thanks guys for all your comments.  I have a new barrel but it requires a rebore and a new top end...$400, when I have only recently spent that on the current barrel. The course of action I have decided to take is rule out the cheap fixes first. The mechanical seal was suspect so I have rebuilt that whole system with all new seals. If it was slowly leaking coolant into the clutch cover it won't now. I have also changed coolant to a blue motorcycle coolant so I rule out the coolant and see a colour change in the oil if it does leak into the gear box, replaced all the tired head studs with brand new Honda studs and after Cooch's very interesting comment, I might go half way and put some teflon washers on each end of the head brace. Don't like the idea of racing a 30 year old motocross frame without all its bracing!

You’re attacking a few issues but it sounds like you haven’t actually confirmed what the problem is yet?

Spending $400 on a barrel doesn’t sound like a cheap fix to me.
Unless the barrel has a crack in the liner then I doubt the barrel is the culprit.

If the mechanical seal was the problem then you would have enough water in the gearbox oil for it to be obvious.

Didn’t you run some clear hoses from the pump to watch water flow?
I doubt the shape of the impellor area was causing enough cavitation for it to overheat (although according to my wife I have been wrong before)

If the head stay is causing the head gasket to break seal or the bolts are pulling through the barrel then the head gasket should have shown signs of leaking. The leak will be from the combustion chamber to the water jacket.
Like wise if the head or barrel was warped.
Did any of the gaskets show any signs of this?
I have heard of head stays breaking heads before, the holes in the brace should be slotted to allow for some ‘give’ so it can cope with frame flex.

My money is still on a cracked head, both the heads.
It bothers me that this is still giving you grief, if you want to post down the old barrel, head and an old head gasket I will have a look at them for you. If I can’t find any cracks in them I will wear the return postage cost.

[Kenneth S (222)]

Thanks Geoff,
Your offer is much appreciated and I might take you up on it.

The head gaskets did let go and there were marks on the head gasket where the combustion gases had leaked through to the cooling jacket. My assessment is that this happened after the head was warped though. I believe there is a good chance that originally the engine overheated because the coolant level dropped to below the point where it would continue to circulate. I want to get the basics right first. Make sure I have a cooling system which is circulating properly and not leaking and then go from there.

I finished putting it together today and started it up and ran it for a while with no incident. I have a race meet this weekend where it will get a work out and see what the score is. The brace is not slotted so I think I am going to put the next size down in bolt diameter into the head stay where it bolts to the head just to give it the 'give' you speak of.

Regards,

Kenneth

[Cooch 04]

So how did it go is the problem solved?

[Ando]

Yes, no steam for the train!

[Scunge]

Sweet! All done!

[Kenneth S (222)]

So how did it go is the problem solved?

Cooch, I kept thinking I should have put something up on here letting you know but I still can't believe it myself and I didn't want to tempt fate. Practice and 3 races and absolutely nothing! The bike performed like a train!

I took the head brace off at the track. Thanks for the tip. One day I might put it back on and see what happens but for now I am going to ride the wheels off it and make up for lost time. 

[Cooch 04]

That's freakin awesum to hear isn't it great when a plan comes together 

[Hoony]

glad to hear its all sorted.

so what was the root cause then?

[suzuki59]

Great work,this is a prime example of the positive nature of this forum.
PS cooch good to see you at Easter I look forward to coming over and catching up with you at a Viper round.

[Kenneth S (222)]

glad to hear its all sorted.

so what was the root cause then?

Hoony,
I believe it was either a faulty mechanical seal allowing the coolant to slowly drain into the gear box to a level where it had stopped circulating and the engine was then overheating or the frame flex was causing the head stay to distort the head, thus blowing the head gasket.


Thanks again to everyone for all your suggestions. We got there!!

[gwc162]

nice work Kenneth  CU @ the nats

[Hoony]

Thanks ken. i admire your persistence. well done.