Situation is thus :-
Kent 1600 XFlow as fitted to TrackToyFour' FF1600. Bone stock as per regulations. Max rpm seen from datalogging ~7100 rpm

The car was recently treated to new exhaust valves on #1 and #4. It's been suffering valve seat recession as the head is not fitted with hardened seats and is running on unleaded. The removed valves were slightly pitted and showed signs of non closure (reason for original head strip was 0 compression on #1 and #4)

Engine ran sweetly during a test day covering some 60 odd laps without mechanical issue

On the next day the engine ran fine for another 10 or so laps of qualification before suddenly developing a top end rattle of significant proportions

A quick check revealed #1 exhaust valve had something like 1/8" clearance
Tappet clearances was reset (Look em up on Google kids ), no sign of issue with the adjusters. All other valves were near enough but were re-tweaked back to perfection so it was an issue sepeific to 1 valve only. Engine buttoned up, assumption was just one of those random events
Come the race the car completed another 6 or 7 competetive laps before a sudden onset of clattery top end. This wasn't stripped down again but the suspicion must be the same thing again.

Engine is currently away for a rebuild so the failure mode is currently unknown.

Given the apparent sudden onset and massive gaps involved I think it's cracked a rocker (google again kids).

Don thinks it's a wear induced follower or cam failure which is also a possibility given that #1 had previously suffered tappet gap closure due to the valve recession

Any other opinions

A friend of mine used to be into Fords in a big way and was always messing about with Pinot and Cologne lumps.

He's still running a Pinto lump in his Robin Hood and i remember he went through about 2-3 sets of cams in a short space of time because of upping the Rev limit too high.

So on that basis i wouldnt be surprised if its a common weak spot on these engines and thats the failure you've got.

Stock limit is something like 5600 isnt it? I dont know what they are built like but i dont think the stock cams would like running over 7k for too long.

Will be interesting to see the results of the strip down

The later xflows didn't have any sort of lock nut on the adjusters, just a tight fit. They were prone to adjusting themselves. Try to find a rocker shaft from an earlier one which had a more conventional screw + locknut.
The rocker face also tended to wear to a cup shape so using a feeler gauge gave a clearance much bigger than required.
I also seem to remember it didn't have valve guide inserts, just a drilled hole in the casting so it was common to have valves wobbling all over the place.

They don't build 'em like they used to

Sadly I think I ditched all my xflow kit years ago.

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If at first you don't suck seed, try drier grain.

Indeed it doesn't have locknuts on the adjusters but given the high rpm nature of the beast I'm not sure adding more additional reciprocating weight is a good plan

The adjusters did seem to be pretty tight still. Maybe they should be replaced with new ones incase there's any wear in them?

It's an unusual one given that the same thing seems to have happened again. Hopefully there will be an update from the engine builder on what they find..

As I said, very prone to adjusting themselves. I think I adjusted mine more often than polishing the car - until I swapped to the earlier ones, and they ran happily to 8K revs. More than can be said for the crank

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If at first you don't suck seed, try drier grain.

Just remembered another problem with the engine is that the rockers are sprung sideways against the posts, and are therefore prone to moving sideways under load once there is wear on the noses. A common trick was to machine up some spacer tubes to replace the springs. Never needed to do this on mine though.

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If at first you don't suck seed, try drier grain.

......due to a valve jammed shut in the head Maybe due to the very worn valve seats 'grabbing' the head of the valve? Fortunately no other damage found...phew!

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Don
GT4DC Chairman
1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
1994 Toyota Celica GT-Four Special GT 590bhp @ 1.8bar
1989 Van Diemen RF88/89 Formula Ford 1600
2008 Nissan Patrol GU 3.0L ZD30DDTi 154bhp