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Giko, the restoration I did was a 1961 aermacchi / HD sprint. Yes, first one and loved it. Did another one afterwards.
Restoration was not that difficult, getting the engine to run was as I toom it completely apart. A lot of trouble shooting. Ended up with same issue: spark fine, gas fine but low compression. The fix was simple but to find the cause was not.

Btw, what is the status? Bike still not running?
 

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Giko - I'm very interested in this as well. I took my bike in for an 8K service about 3 weeks ago. I rode it home - about 20 miles, then started it briefly about a week ago. I went to start it today and it's making the exact same noise yours was upon starting (never fires to idle). I have no idea what happened.
 

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Discussion Starter #44 (Edited)
Long overdue update...

Long overdue update…

So I recently had some time and I started working on my engine. Here is my compression result:
Dry compression test 30PSI
Wet compression test 60PSI - tablespoon of oil in the cylinder
Note all compression test were with Wide Open Throttle
This would suggest more likely problem with the rings than with the valves.

My valve clearance was as follows:
IN valve clearance Both 0.13mm
EX valve clearance Left 0.18mm, Right 0.23mm

Valve clearance should be:
IN 0.16mm (+-0.03mm) - 0.13 to 0.19mm
EX 0.27mm (+-0.03mm) - 0.24 to 0.30mm

The IN clearance was border line and EX is tight.

So I took the engine out and this is what it looks like.
You can see all pics in this link:

https://plus.google.com/photos/116190529240870307837/albums/5961799949317740097?authkey=COi5la7NwJPhaA

Two compression rings were seized. The oil rings were fine.
I did the leak test on the valves and I was getting minimal leakage. Half a drop in 3H.

I have to say that I’m not a mechanic and this is very first time i’m actually holding a piston. I’m looking for your guys assessment and advice.

Since the engine overheated, I figure that I should replace the cylinder, piston, and gaskets.

I believe that the head should be okay to be reused, but I will reseat/lap the valves.
Any advice?
 

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The compression figures speak for themselves - definitely far too low. What is baffling is that the rings are seized without any major wear on the cylinder bore ( at least in your pictures). Could the engine have had water damage? You should also be checking for basic mechanical faults such as valve timing being way off or conrod bent.

Regards Roadster
 

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Discussion Starter #46
thanks you for the info Roadster,
I will upload more cylinder pics in two weeks when I will be back home. I can tell you the the pic of the cylinder bore was the worst side (of the cylider bore) showing the vertical line.
I will also inspect the cylinder and conrod.
I don't see how the bike got water damage...The bike was parked inside all the time since the very last ride. However my very last ride was in pouring rain for about 3H and 300km. I got home and it did seem like it had less power, but id definitely ran.
How can I check if the timing is way off now that the engine is apart? I don't think I can...Keep in mind that this is the very first time I'm working on the engine
Could the seizure been explain by excess carbon build up? or that the engine was overheated when it was at 2000km?
 

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thanks you for the info Roadster,
I will upload more cylinder pics in two weeks when I will be back home. I can tell you the the pic of the cylinder bore was the worst side (of the cylider bore) showing the vertical line.
I will also inspect the cylinder and conrod.
I don't see how the bike got water damage...The bike was parked inside all the time since the very last ride. However my very last ride was in pouring rain for about 3H and 300km. I got home and it did seem like it had less power, but id definitely ran.
How can I check if the timing is way off now that the engine is apart? I don't think I can...Keep in mind that this is the very first time I'm working on the engine
Could the seizure been explain by excess carbon build up? or that the engine was overheated when it was at 2000km?
Yes its too late to check whether the timing chain had jumped its sprockets although you can check that the tensioner and guide blades are OK.

It seems unlikely that you would have been able to cover 8000 km since overheating if something had been seriously wrong and I think you would have heard and seen any issue caused by distorted cylinder head and leaking gasket. The part of the cylinder bore which I could see seemed to still have original honing pattern. Is this uniform across the entire area of the bore? You may need to get the barrel professionally inspected and measured to make sure it is in spec. and not deformed. Maybe someone with experience of these engines can say whether this is the normal appearance?

Taking account of the poor condition of the piston and the unusual appearance of the bore it seems plausible that the rings have been damaged and seized since the overheating incident and they have gradually got worse to the point were a cold engine has too much piston clearance to run.

It would probably be false economy to try to use the old piston even if the barrel checks out OK.

Regards Roadster
 

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Discussion Starter #48
It would probably be false economy to try to use the old piston even if the barrel checks out OK.
I got myself a dial bore gauge and took the measurements. It took me a while to figure out how it works. Here is what I found:
The bottom of the cylinder was good and round I got the same reading left-right VS front-back. Middle was off by about 0.0005". The top of the cylinder was way off with 0.0020" difference. Front-back diameter was longer than left-right diameter. So basically the top of my cylinder is OVAL.
Service manual limit for out-of-round is 0.004" so I am 5 times over the limit.
Needles to say I will be ordering a new cylinder.

I also inspected the play between the con-rod and the crank shaft and its solid (when pulling towards and away from the crankshaft).
There is very little play side to side, I believe that it should be okay.
 

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I got myself a dial bore gauge and took the measurements. It took me a while to figure out how it works. Here is what I found:
The bottom of the cylinder was good and round I got the same reading left-right VS front-back. Middle was off by about 0.0005". The top of the cylinder was way off with 0.0020" difference. Front-back diameter was longer than left-right diameter. So basically the top of my cylinder is OVAL.
Service manual limit for out-of-round is 0.004" so I am 5 times over the limit.
Needles to say I will be ordering a new cylinder.

I also inspected the play between the con-rod and the crank shaft and its solid (when pulling towards and away from the crankshaft).
There is very little play side to side, I believe that it should be okay.
Have you got some extra zeros in there somewhere? If the limit is 4 thou ( thousandths of an inch) 2 thou is just half of that. i.e. 0.002 is half of 0.004
Do you mean that it was out by 0.020 ( 20 thou)?

Regards Roadster
 

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Discussion Starter #50
Do you mean that it was out by 0.020 ( 20 thou)?

Regards Roadster
I measured the diameter once (front-back) and than at 90deg (left-right). So the difference between one to another was 0.020 (20 thou)
So if we could say that one diameter measurement was 0.010 (10 thou) longer than normal and the other diameter was 0.010 shorter than norm. Between the two was 20 thou difference.
I hope that i'm making sense....
Sounds excessive?
 

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Discussion Starter #51 (Edited)
I removed the valves today and I found this.
There is a crack inside both Intake valve ports.

https://docs.google.com/file/d/0B1KwundKmdKURFdkWFpTVGs4REU/edit?usp=drivesdk
I called a local machine shops.
One said to bring it in for a look and the other said that the cost to repair it will be way more than $130 which is the cost of the new head.
Could this explain high carbon build up and oil consumption?
 

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Discussion Starter #53
I can't really see the crack in your picture. Is it the valve seat insert that's cracked or the cylinder head itself?
Its the white line in front of the arrow. The crack (or grove) is on the head about 1mm from the valve seat insert.
It's more like a grove since it does not go all the way through.
 

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Its the white line in front of the arrow. The crack (or grove) is on the head about 1mm from the valve seat insert.
It's more like a grove since it does not go all the way through.
I see what you mean but it doesn't look like a crack from the picture. I would probably clean the surface with emery cloth then examine it again. If you are not satisfied with visual inspection it is possible to get a crack detection 3 part spray kit. These are typically used to check welds but should work on alloy.

Regards Roadster
 

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Discussion Starter #55
UPDATE:
Bike is running!!!
I rebuilded the top end myself and it runs. After speaking to a tech at a machine shop, I decided to reuse the head. He did not think that the problem with the valves serious. I did replace the cylinder, piston, and I laped the valves.

When the engine failed I felt like droping the whole bike of the cliff and watch it brake in to 1000 pices. I was so down and I thought I had the worst luck (buing a used bike). Now I can say that the engine failure was a blessing. I really enjoyed rebuilding it, and will even say that this is my new hobby. I might even take it all apart durring next winter...
Today when I started it and heard it come alive,... it felt really good.

Technical details
I tried to stick to the service manula as much as possible. Since the manual did not call for honing of the cylinder, I did not do that. The new cylinder did came with a cross-hatched pattern, which looked identical to the old cylinder. One corner that I did cut was when I reused the original connectors when re-connecting fuel pump. The manual called for using a new piece. I carefully inspectd the connector and found it to be in good shape, flimsy but mine was okay so I reused it.
I'm vary happy to be back in the sadle :)

thank you all for the help.

Roadster, beer is on my if you are ever in Nova Scotia :)
 

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Hi Giko....found your thread very interesting, because my bike is suffering from almost the exact same symptoms as you were suffering from. Would like to do a compression check but my compression gauge has 2 adapters with it and neither one is even close to the proper size, so just wondering where you got the proper size adapter for the cbr250 spark plug hole. Also where did you get most of your new engine parts? Local or mail order. I live in Lower Sackville, so any information you can give me would be very helpful if the parts were sourced locally. And any chance you can give me a ball park figure on the cost of your rebuilt.........
Thanks in advance from a fellow Bluenoser.....
Aaron
 

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Discussion Starter #59 (Edited)
PM send
BTW
The engine is still running well. Last June I rode the bike from Halifax to Toronto through New England 1850km. Epic ride, way better than Trans Canada Hwy. Last 400km were WOT for 4 hours (just a petro break).
 
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