Monday, February 10, 2014

Rebuilding the Head

This is an area I have worked with several times before and there was not a big learning curve, although I tried a few new things.  Valve adjustments had been neglected and one of the valve stems was peened over. I ground off the stem of the offending valve and tapped it out.  When the valves were out I heated up the head in an oven and pressed out the old guides with a simple press I made. I have used a punch in the past but elected to try the press this time. It worked well and I will use it for future rebuilds. Pictures of the tools I used are below. This is also where I had a learning experience for next time. I bought nominal sized outer diameter guides with undersized bores. I purchased a valve guide hand reamer from Cylinder Head Supply to take the guide inner diameters to size. I also obtained a lap to finish the inside of the valve guides. From what I understand this is critical for valve guide life. The lap leaves an excellent finish and this makes sense to me. I should have also purchased a hand reamer to clean up the scoring in the aluminum. I suspect that galling in the head caused the guides to be a slight bit off center when they were installed. This is not a problem as everything cleaned up but it will improve my process next time.

A picture of the head as removed from the bike. 

Valves & guides removed. 

After the new guides were installed I ported and polished the head. I matched the ports up with the intake gaskets, which were already pretty close, and cleaned up the flash in the exhaust ports. I did not reshape anything and elected to take off a minimal amount of material. I focused on getting a uniform finish to 320 grit paper to facilitate flow. If you want top notch performance you should take your head to someone with a flow bench and experience working with BSA’s. I have no plans to race this bike but want it to perform well so I chose the route I did. If you are not confident in your ability to handle an air grinder on aluminum I would leave this job to someone else. It would be pretty easy to ruin a head. My experience benching and polishing aluminum in the tool and die trade gave me confidence to approach this job. I am happy with the results although I will not know how well I have done until I get it running.

Once the head was ported and polished I used a set of Neway valve seat cutters to clean up the valve seats. After they were lightly machined all around I lapped the valves so no light would show around them in a darkened room. This took about an hour per seat to accomplish but the final result looks good. 

Intake port matched to the gasket and polished. 

Exhaust port casting cleaned up. 

The tools used to recondition the head. 

Valve seats cut & lapped. 

Assembled head ready to go. 

Elephant foot valve adjusters. 

As far as parts go I used OEM spec springs and keepers, Black Diamond valves and elephant feet adjusters. Yes, I realize that I cannot get the head bolts installed since I have put in the front rocker arm shaft. I figured this out shortly after assembly. Lesson learned……again #$&#!!! 

Monday, February 3, 2014

Turning Brake Drums

The brake drums were rusted and I suspected they were out of round. I made a simple fixture by machining aluminum round stock to accept the hub bearing surface. A bolt in the center was used to draw the hub down to it. The fixture was machined in a 3 jaw chuck and the hub put onto it without removing it from the lathe. This ensured everything ran concentric. If this fixture is setup again it will be put into a 4 jaw chuck and indicated concentric.  

A simple fixture turned in a 3 jaw chuck.  

 The hub was checked with a dial test indicator to see how far out of round it was. 
It measured .005 inches out on the radius. 

Very light cuts were taken and the drum was opened up about .020 in on the diameter. This is the minimum amount that could be removed and still get it to clean up. The resulting finish is good and new brake shoes will be fit to the larger diameter. Both drums were refinished in this manner.