jollygreengiant
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| posted on 10/5/21 at 08:04 AM |
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Just to throw a odd shaped spanner into the mix.
It IS possible to use a FLAT full race Xflow head WITH flat pistons. BUT you do need to know what you are doing.
Back in 1980, I home built a mother of a Xflow to go into my Mk1 Cortina, everyone said "nah, it work work/run nice". It worked and BOY
did it have some ooooomph.
711M block with the crank reground 10/10/std, re-bored to take Std (bore) Lotus Twincam (PowerMax/Hepolite) Pistons (1662cc in the Xflow block and
relatively flat pistons).
Flat FULL race head (with the biggest valves that could be fitted into the cylider bore/space between the valves and allowing for heat expansion off
the valve face, yes that is a factor when your valves end up that close together).
The trick was to make space between the valve face and the flat piston. this was done in 2 stages. Firstly the (then VERY expensive pistons, funny bit
was, the machine shop HAD to buy a second set as the machinist screwed the pooch on ONE of my pistons) pistons had there chamber faces machined flat
to removed the inclined valve pockets (25thou rings a bell).
Secondly the block was then machined (with much reassembly work) to give a working C.R. of 11:1 (we were trying to go 11.5:11 but could not).
The whole lot was weight matched and balanced, then toughened, heat treated and balance rechecked. the assembled and run with a Full race Cam, Piper
Ladder rocker gear and Twin 40 DCOE's.
Once run in, it was a beast. 30 MPG when cruised up the motorway at 70 (about 3800 rpm using a 3.7 diff), but the real fun was that the engine would
pull 8k in top gear. Quicker that the (then) new 2.8 injection Capri's.
Don't loose heart it can be done and you can get really good figures/use out of the Xflow engine.
The only down side was that plod used to pull me (strangely always a different one, on the same road at the same time) about twice a week (sometimes
more) for a "Document Check" (every time they ended up looking under the bonnet), It got so bad that I used to produce them at about 2am
in Wellingborough station and after a little while, I used to walk in, the Desk Sergeant would look up, say "Oh Hello Mr Taylor, Documents
Again", then pull out his book and tick off the appropriate section(s), without looking at my documents, only looking at the PC's numbers
on the producers. I guess it must have been a right of passage for the Road Traffic Squad. 
Beware of the Goldfish in the tulip mines. The ONLY defence against them is smoking peanut butter sandwiches.
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adithorp
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| posted on 10/5/21 at 08:40 AM |
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Haven't seen it mentioned yet so...
Make sure you check the rockers and push rods. With the valves hitting the pistons they might have been damaged. Pushrods tend to get bent by valve
impacts, though I suspect you'll have got away with it. Rods have probably only flexed.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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Deckman001
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| posted on 14/5/21 at 02:11 PM |
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Hi again, sorry been off line for a while sorting room changes and no computers connected. The pistons are bowl'd type and the original engine
was built by others before i got it so I assumed i could just change the head. Yes I also got a high lift cam and forgot to check the clearances.. The
bottom end was built and installed before the head was delivered and turned over very freely. The refurbished head was bolted to the bottom end and it
turned over very easily and fired up straight away. It was a bit noisier than expected but I just thought something was worn that i put back in but it
also sounded so fantastic with bike carbs and big bore exhaust i just got carried away and used it for the IVA retest a few days later, I
couldn't put the retest back as it was the last days for the retest before it needed a whole new test instead. It pulled like a train when over
2000 revs and it always pinned me back to my seat when the pedal was pushed too hard. Below 2k though it was very flat and I eventually realised i
needed to change down when at low revs and bid load like a hill.
Rocker gear looks great still along with the push rods all looking correct and straight.
The pistons had been hit towards the tops of the bowls so thankfully the thinnest parts of the pistons, which is hopefully why the bottom end looks
brand new still.
When the head comes back from the garage I will be dry assembling it to check clearances before i strip it again and build up the bottom end again,
get it back into the car before i then put the head and ancillaries back together to risk the restart.
No news yet as to when I get the chambered head back once it's refurbished.
Jason
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rusty nuts
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| posted on 14/5/21 at 04:29 PM |
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I did mention checking the valve to piston clearances on your “ my old locost has come home “ thread last November!
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Deckman001
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| posted on 16/5/21 at 01:52 PM |
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Yeah, but I had wrongly assumed that the new head should be the same along with bowled pistons and a slightly high lift cam will be ok, sadly it
wasn't and I should have rechecked it. I was rushing to get it started due to my retest dates being the last attempt to get an IVA pass. At
least the engine lasted long enough for the pass so the car can now just wait until i get the engine rebuilt correctly and checked along the way.
Jason
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