SU piston stop cushion

Technical advice Q&A

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40GT
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Location: Herefordshire
Great Britain

#1 SU piston stop cushion

Post by 40GT » Thu May 21, 2026 6:28 pm

Anyone know the tolerance for the nylon stopper insert on the piston underside, ( damper cushion for piston drop to throat bridge ) , the SU part number for the smaller carbs is AUD 2435 and the air gap is 8 - 12 thou, but I think this is only for HS4/6 carbs, the HD8 having a separate air bypass which avoids the possible piston drop engine stall effect.
I will call SU tomorrow, but just thought if someone here has already been here.
Sean

S1 2+2 1966 BW RHD
XK120 1954 comp LHD

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Topic author
40GT
Posts: 62
Joined: Wed Nov 20, 2024 9:22 pm
Location: Herefordshire
Great Britain

#2 Re: SU piston stop cushion

Post by 40GT » Thu May 28, 2026 6:25 pm

So, after a call to SU, they confirmed the above part number and tolerance is correct for the HD8.
The parts arrived and were fitted yesterday.
Pressed in and lathe set to 10thou protrusion, air screws adjusted slightly and she's very happy.

If you have a gap at the front part of the bridge to piston of below .005 or a difference between carbs, it's well worth doing and they cost 48pence each.
Sean

S1 2+2 1966 BW RHD
XK120 1954 comp LHD

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mgcjag
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#3 Re: SU piston stop cushion

Post by mgcjag » Thu May 28, 2026 6:44 pm

Thanks for posting....Great info...
Steve
Steve
69 S2 2+2 (sold) ..Realm C type replica, 1960 xk150fhc

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