AlfaGTA
Diamond
- Joined
- Dec 13, 2002
- Location
- Benicia California USA
Some light entertainment here....
Big scramble this week.
Have an Alfa Romeo 6-C 2500 engine that is nearing completion that needed some TLC.
This is an engine that Alfa made is some numbers from 1938 through 1952.
Twin cam iron block with an aluminum head....
Anyhow this project was just back from running on the dyno...in effect finished.
On the post Dyno work the spark plugs were removed to install a fresh set....
Trouble is that the head originally built with 18mm spark plugs, has had inserts fitted to allow use of 14mm plugs.
Of course a number of the inserts decided to come out with the plugs, and in so doing buggered the 18mm threads.
Normally this would be a small matter. Remove the head and set it up on the mill and install thread inserts to repair the damaged threads....
Further it was deemed important to return the head back to using the 18mm plugs as originally built.
Problem is that getting a new head gasket in short order (promised delivery schedule) was not in the cards........
Now for those familiar with spark plug repairs, there is a relatively simple fix to over tap for an STI insert. Kit consists of a special stepped tap.
Having the 18mm thread at the end for a short portion, and then a tapered reamer portion leading to the 18mm "STI" tap ....
Theory is that the small thread starts in the original thread (what is left) and as you thread it in the tapered reamer portion opens the hole up to accept the oversize
STI tap....This more or less gets the threads started true to the original plug thread, and gets a good hole for the oversized tap portion....
Well here this setup does not work! The head is made with what i call a "fire slot" ...the spark plug actually fits into a bore that has a floor that is machined with a small slot
that enters the actual cylinder chamber....This arrangement was used by Alfa in lots of their engines...Seems to give better control of the burn with poor fuels.
Anyhow the net effect is that there is no through hole into the chamber so no trick aligning tap.
Solution seemed to be that there needed to be an accurate way to drill and tap the insert hole/threads....All requirements pointed to using a machine.....
We own two Deckel FP4NC's. An early "camel back" that i run almost every day...fitted with the "Tool Makers Table" (2038)
And a later "Flip" having the rigid table.....
It was decided that due to height needs the "Flip" was the best option. Having the rigid table mounted roughly 3.5" lower than the 2038 would provide just enough vertical height to
enable my repair [plan.
So here is the basic setup:
Fully assembled engine, stand up on bell housing mounting flange of the block.
Use horizontal spindle to bore damaged plug hole and align tap for threading for thread insert....
Fully assembled engine, need to contain any chips from entering the engine.
Alignment to the plug hole was accomplished by tramming the ground shank of an 18mm tap run into the original plug hole.
This allowed indicating in 2 planes using the top and side of the tap shank.....Adjusting the engine to be flat in the horizontal plane was accomplished using feeler stock under the
bell housing mounting flange and screw jack.
Finding the center of the original plug hole was done using a modified spark plug.....Removing the insulator form a normal spark plug leaves a concentric ID bore that once the plug is screwed into the head
provides an indicating surface to align the center of the machine spindle....
As to the issue of chips....my solution was to make an adapter pipe that fit to the engine's exhaust flange.....
to that pipe i connected a hose from the exhaust side of out shop vacuum.....
The engine was rotated until the exhaust valve was open on the cylinder being repaired.....
The vacuum turned on and air forced out during the machining operation......
In all three spark plugs (of 6) were repaired.....In all a good job.
In order to get to the final plug (#6) the engine was lifted and placed up on 2,4,6 blocks to give the needed height. Of course realignment was required after the lift......
Side note here:
In order to do this job, i needed to remove and clean the "X" axis scale. Machine had been down with a fault on the scale, and this job pushed that repair to the front....
Cheers Ross
Big scramble this week.
Have an Alfa Romeo 6-C 2500 engine that is nearing completion that needed some TLC.
This is an engine that Alfa made is some numbers from 1938 through 1952.
Twin cam iron block with an aluminum head....
Anyhow this project was just back from running on the dyno...in effect finished.
On the post Dyno work the spark plugs were removed to install a fresh set....
Trouble is that the head originally built with 18mm spark plugs, has had inserts fitted to allow use of 14mm plugs.
Of course a number of the inserts decided to come out with the plugs, and in so doing buggered the 18mm threads.
Normally this would be a small matter. Remove the head and set it up on the mill and install thread inserts to repair the damaged threads....
Further it was deemed important to return the head back to using the 18mm plugs as originally built.
Problem is that getting a new head gasket in short order (promised delivery schedule) was not in the cards........
Now for those familiar with spark plug repairs, there is a relatively simple fix to over tap for an STI insert. Kit consists of a special stepped tap.
Having the 18mm thread at the end for a short portion, and then a tapered reamer portion leading to the 18mm "STI" tap ....
Theory is that the small thread starts in the original thread (what is left) and as you thread it in the tapered reamer portion opens the hole up to accept the oversize
STI tap....This more or less gets the threads started true to the original plug thread, and gets a good hole for the oversized tap portion....
Well here this setup does not work! The head is made with what i call a "fire slot" ...the spark plug actually fits into a bore that has a floor that is machined with a small slot
that enters the actual cylinder chamber....This arrangement was used by Alfa in lots of their engines...Seems to give better control of the burn with poor fuels.
Anyhow the net effect is that there is no through hole into the chamber so no trick aligning tap.
Solution seemed to be that there needed to be an accurate way to drill and tap the insert hole/threads....All requirements pointed to using a machine.....
We own two Deckel FP4NC's. An early "camel back" that i run almost every day...fitted with the "Tool Makers Table" (2038)
And a later "Flip" having the rigid table.....
It was decided that due to height needs the "Flip" was the best option. Having the rigid table mounted roughly 3.5" lower than the 2038 would provide just enough vertical height to
enable my repair [plan.
So here is the basic setup:
Fully assembled engine, stand up on bell housing mounting flange of the block.
Use horizontal spindle to bore damaged plug hole and align tap for threading for thread insert....
Fully assembled engine, need to contain any chips from entering the engine.
Alignment to the plug hole was accomplished by tramming the ground shank of an 18mm tap run into the original plug hole.
This allowed indicating in 2 planes using the top and side of the tap shank.....Adjusting the engine to be flat in the horizontal plane was accomplished using feeler stock under the
bell housing mounting flange and screw jack.
Finding the center of the original plug hole was done using a modified spark plug.....Removing the insulator form a normal spark plug leaves a concentric ID bore that once the plug is screwed into the head
provides an indicating surface to align the center of the machine spindle....
As to the issue of chips....my solution was to make an adapter pipe that fit to the engine's exhaust flange.....
to that pipe i connected a hose from the exhaust side of out shop vacuum.....
The engine was rotated until the exhaust valve was open on the cylinder being repaired.....
The vacuum turned on and air forced out during the machining operation......
In all three spark plugs (of 6) were repaired.....In all a good job.
In order to get to the final plug (#6) the engine was lifted and placed up on 2,4,6 blocks to give the needed height. Of course realignment was required after the lift......
Side note here:
In order to do this job, i needed to remove and clean the "X" axis scale. Machine had been down with a fault on the scale, and this job pushed that repair to the front....
Cheers Ross