CRF250R 2008 decompressor
Posted: Sat Aug 28, 2021 11:13 am
Hi!
Long time ago I bought CRF250R 2008 In a box, competely trashed, with exhaust valve broken and destroyed head.
After 2 years of thinking what to do with it I started to completely rebuild it.
Engine is almost ready, but I have 2 consernes regarding it, and hope that this is the place where someone could clarify them for me.
1) 2008 CRF250R is single cam engine, with marks on cam sprocket with 180 degrees between them. I managed to install cam with all marks being where they should be, Piston in TDC and cam marks in line with head. But after that I got worried that in theory you can install cam wrong way, (by turning it 180'degrees). After looking through manuals, I think I installed it correctly. Intake cam lobes are facing intake side. (as shown in manuals). But when I turn engine with kickstarter, after TDC first valves that start to open are exhaust valves. In some forums I found that after TDC intake valves should open... Which one is correct?
2) I didnt disassemble decompressor, but installed as it was when I received it. But ... When I turn engine slowly as soon as decompressor shaft meets exhaust cam arm, it gets pressed to one side, and as soon as it passes it, it jumps back to middle with uncomfortable clanking sound. When you manually turn weight up on end of cam, that decompressor shaft turns and passes arm smoothly without any sounds. Am I just worrying too much, or its something wrong with it ?
3) I think I shimmed my gearbox correctly, with all washers just like in spare part book, but still from countershaft or mainshaft (dont know which is which) (shaft where small sprocket mounts) I still get like ~0.7mm movement inside-outside, is it something wrong with it and I should brake engine open again, or it is normal with CRF's ?
Big thanks on any answers in advance.
Long time ago I bought CRF250R 2008 In a box, competely trashed, with exhaust valve broken and destroyed head.
After 2 years of thinking what to do with it I started to completely rebuild it.
Engine is almost ready, but I have 2 consernes regarding it, and hope that this is the place where someone could clarify them for me.
1) 2008 CRF250R is single cam engine, with marks on cam sprocket with 180 degrees between them. I managed to install cam with all marks being where they should be, Piston in TDC and cam marks in line with head. But after that I got worried that in theory you can install cam wrong way, (by turning it 180'degrees). After looking through manuals, I think I installed it correctly. Intake cam lobes are facing intake side. (as shown in manuals). But when I turn engine with kickstarter, after TDC first valves that start to open are exhaust valves. In some forums I found that after TDC intake valves should open... Which one is correct?
2) I didnt disassemble decompressor, but installed as it was when I received it. But ... When I turn engine slowly as soon as decompressor shaft meets exhaust cam arm, it gets pressed to one side, and as soon as it passes it, it jumps back to middle with uncomfortable clanking sound. When you manually turn weight up on end of cam, that decompressor shaft turns and passes arm smoothly without any sounds. Am I just worrying too much, or its something wrong with it ?
3) I think I shimmed my gearbox correctly, with all washers just like in spare part book, but still from countershaft or mainshaft (dont know which is which) (shaft where small sprocket mounts) I still get like ~0.7mm movement inside-outside, is it something wrong with it and I should brake engine open again, or it is normal with CRF's ?
Big thanks on any answers in advance.
