jrsunt Posted October 12 Report Share Posted October 12 My well used and abused 2006 bike is ready for full engine rebuild. Con rod, piston, cylinder, cam chain and head work. The con rod is straight from a CRF 250 and will have to be aftermarket as a genuine Honda part is only available as a full crank set ££££ The piston, cylinder etc are fairly straight forward, but I’ve never delved in to a cylinder head. I’m presuming valves will be need to be replaced and the seats re cutting and profiling which I will be getting someone else to do as I don’t have the tools to do them, whilst the head is off and stripped I thought I’d get it gas flowed. Anyone have any thoughts or experience with this? After reading the service manual, the valve stem and valve guides need measuring together and against new valves (which I have) to determine whether new valve guides are needed. These valve guides DON’T exist in the parts list or drawings. Any thoughts on this? The cylinder head, cam, valves and everything in between have not changed from the original 2005 250 engine right through to the current 301. I was surprised by that too, and again the valve guides don’t exist in any parts diagrams. Again, has anyone had any experience on cylinder head work on bikes in general and any thoughts on the allusive valve guides? Thanks Quote Link to comment Share on other sites More sharing options...
konrad Posted October 12 Report Share Posted October 12 I have a little experience with this. As you know, replacing the guides is not typically a DIY job. After installation, the ID needs to be reamed to size and the seats re-cut. The US company Kibblewhite manufactures aftermarket valve guides (and other head components as well). See: https://www.kpmi.us/ The potential problem I see with gas-flowing the ports is that the technique is generally used to improve WOT flow. Unless the person doing the work has experience specifically with trials, the results may actually make the performance worse. Quote Link to comment Share on other sites More sharing options...
jrsunt Posted November 5 Author Report Share Posted November 5 After a bit of time on the google, I found Ben Coyle Racing for the head and crank jobs. He was familiar with the 4rt and knowledge about trials. After a quick phone call, gas flowing was ruled out as the process moves power around. What you gain in one area you lose in another, but a head clean up and polish would help things. The valve guides wouldn’t be a problem either as they custom make them for race engines. I’ve nearly all the parts gathered up, just the con rod and big end to decide on. The dogs dangles of rods is the CP Carrillo at around £280, but they don’t supply the crank pin, bearing or washers. So another manufacturer needs to be considered for those. In my mind, it appears to be pointless to put best rod in and then have to compromise on the pin and bearing. The next best option seems to be Wossner or Pro X for the complete kit at £120ish Quote Link to comment Share on other sites More sharing options...
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