Hi guys,
I'm just wondering how a machinist goes about centering the dome perfectly to be able to drill and dowel it?
Quote from: rd400canuck on December 06, 2020, 01:30:35 PM
Hi guys,
I'm just wondering how a machinist goes about centering the dome perfectly to be able to drill and dowel it?
By using the spark plug thread as origin. If the head is modified for squish or changed CR, he would have used a mandrel to hold it in the chuck. Then one could use the same mandrel, screwed in from the combustion chambers side, and make a slip fit sleeve for it, with the sleeve OD slightly smaller than the cylinder bore. Aluminium, plastic or even brass would be a good sleeve material. If the sleeve is made for stock bore, brass shim stock could be used to compensate for larger bores.
I made a jig
thanks guys!
Another way to insure the head and bore are concentric is to bolt the cyl & head together, drill for pinning holes, scribe bore to head, separate head and cylinder, use mandrel in 4 jaw chuck and center scribed line by adjusting chuck to establish squish is aligned to bore. Sparkplug holes are usually off center a few thousandths from bolt holes.
Does anyone have a picture of where the dowels/pins go when doing this? I had thought that the dowel would be in a blind hole in the head and cylinder but after reading drilling as a set bolted together I am guessing that is not the case.
2 different ways I have seen it done
(https://uploads.tapatalk-cdn.com/20201208/44e894c0e562fe2b9b2a38a4594284a6.jpg)
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The top picture of the head in Rodneyas' post is how I do our personal engines but I machine a stepped sleeve insert and put the smallest diameter in the head. After doweling we bolt cyl & head together and scribe head so combustion chamber is concentric when machined. Have to use pinned as shown in other pictures when RD's are converted to bolt down style.
looking at machining is like looking at porn for me... actually better.
This is a pretty easy project for an engine with a concentric spark plug hole and split heads. Doing this on something like GT750 takes a bit more process.
That said, I need to do this to my 350.
When I do this modification I bore my cylinders first then put them in the mill find center of the bore then put the dowel pins and o ring in. I then fixture the heads in the mill find the spark plug and machine the heads with a cnc mill and dowel pin. This allows me to machine Daytona heads and not cut them in half as well both heads being perfectly the same.
Check out my sight for pictures.
Gra2strokes.com
Garrett