Looking at the junk thrown on the market by SIR its easy to spot their

handy work....BTW I saw another one of their heads that dropped a seat

yesterday,it had less than 3,000 miles running time.......First off it seems

the dual ports type 1s are more prone to cracking than the single ports type

1s....The most common areas for cracks are between the seats,intake and

exhaust or from seat to plug hole.....The worst ones crack both

places....Once the plug hole cracks sooner or later the plug blows out of the

hole creating another problem ;-) In their quest to repair worn out

cracked heads the rebuilders weld up and redrill the plug holes,leaving globs

of weld off to the side.....Next the attempt to weld broken cooling fins back

on leaving obvious grind marks and more shoddy workmanship for you....If the

seats are cracked they attempt to rout out the crack using a rotary file and

hopefully get it all.....Then they hopefully select the right welding rod and

attempt to fill the gaping crater cause by routing out the crack......Finally

they return the combustion chamber to a size near stock but make no attempt

to properly match CCs.....Add to this reusing old valve springs,keepers and

sometimes valve guides if they are marginal......They sometimes crack guide

bosses when installing guides and make no attempt to fix,its up to you to

carefully inspect the garbage uh er heads....I have gone through piles of

rebuilt heads looking for something that would work because the customer

specified rebuilt heads .....The intake valves because they are cooled by the

fuel air mixture also get reused ,and hopefully they replace the exhaust

valves,but even if they do its with the cheapies.....What you get is

mismatched,old possibly overheated jury rigged parts that may go 3,000 miles

or perhaps 50,000 and beyond ..Nobody has a clue because the heads arent

serialized and records arent kept.....Bottom line avoid rebuilt heads if you

are building anything you are planning to keep....Spend the extra 50.00 and

buy new so you have piece of mind.....

Zundfolge1432