Herald pistons - differences in 1200 engines, early and late?

[Colin Lindsay]

I'm working on two Herald engines at present, one from 1962 and one from 1967. I've already found substantial differences in the heads but whilst researching pistons I've found that some dealers will sell pistons as suitable for 1961 - 1965, and others as a one size fits all from 1961 - 1970. 

I've found hints of changes at GA80000 - prior to this is referred to by some as the 39bhp engine - whilst others will sell parts up to pre 1966 or post 1966. I'm nearly certain this only affects the head, which was redesigned regarding coolant flow etc. I'm keeping like for like regarding original heads with blocks, camshafts etc so it's only the lower end that's causing doubt.

I can't find any reference of changes to the block or lower engine, but I just want to make sure before I commit to purchase; does anyone know if there were any changes that might affect the piston required? 

[Pete Lewis]

my wsm shows  solid skirt intro ga137545   gd21229    fc24449   compression ring groove of  0.0807" / 0.0797"

if thats any use  

Pete

[Nick Jones]

Pistons likely to interchangeable even if different.  At some point the cam follower diameter changed (increased to 0.8” IIRC) and possibly some breather changes. My 64 built 1200 had an open breather tube on the rhs under the manifolds. Later engines were blank. I have also seen them with core plugs fitted in the hole.

Nick

[DanMi]

As far as I know the difference was as Pete says split v solid skirt. The early pistons had an extra oil control ring below the gudgeon pin (split skirrt) these proved to be a bit weak on the more powerful (particularly the higher tuned spitfire engine) so they went to solid skirt. the later ones can be used in any 1147 engine but I wouldn't put the split skirt in my MK2 spitfire. The other difference (not sure it applies to heralds) is most 1147 engine had small end bearings with gudgeon pins held in place by circlips some spit engines had no small ends and gudgeon pins that were pressed in so no circlips. Either can be used so long as the pistons match the conrods. The other difference in the lower engine is the rear oil seal, early cars had the scroll type later had a rubber oil seal. Again interchangeable as long as the oil seal housing matches the crank.

[DanMi]

ps I have a set of NOS hepolite split skirt pistons +0.020 with PEP top ring in the loft bought fro ebay b4 I relised the difference when rebuilding my spit engine

 

[Nigel Clark]

I was involved in stripping an 1147cc Herald engine last week, with an engine number just a few below GA50000. For what it's worth, the pistons appeared original and had split skirts with gudgeon pins retained by circlips.

Nigel

[Colin Lindsay]

22 minutes ago, Nigel Clark said:

I was involved in stripping an 1147cc Herald engine last week, with an engine number just a few below GA50000. For what it's worth, the pistons appeared original and had split skirts with gudgeon pins retained by circlips.

Nigel

These are the pistons from the later 1967 engine; the early ones are still in the block until work progresses that far. These are the ones that I need to replace more urgently once block boring work is complete.

If, as Dan says, I can use later pistons on all then that sounds good; if they were strengthened to reflect the power increase caused by the other modifications that they should in theory be suitable for all whereas the earlier pistons won't last in the newer engines. Makes sense.

The interesting thing is that one seller selling sets of Hepolites on eBay has two sets for Herald and Spitfire, one early and one late, but yet he is showing the same label for each sale; earlies are £80 and lates are £60 for the set - see the lower pic for what they look like boxed. It's a substantial saving over what the engine-work companies are charging me if they supply, but only if they'll fit a GA229***HE block. The earlier block is GA119***HE which going by Pete's post would be split skirt, but I now assuming can be changed to solid easily enough?

  

[DanMi]

just looked in the loft hepolite Nos 

Split skirt  16178  fine for the early lower powered herald 1200 and prob even the 1250 but not ideal for the 67hp spitfire

solid skirt with small end 18690  

press fit solid skirt   18261 these are rare

Most sellers simply put 18690 even if split skirt hence the no written in pencil which is why I bought a set which I have never used. 

[Colin Lindsay]

These are 16178 but he's added 18690 on the box in marker. The funny thing is that they're two different boxes, going by the writing he's added on the front, yet both the same pistons, same reference numbers, same labels, but £20 difference.

I don't yet need pistons, only rings, as the wear to the bores is amazingly slight and I might get away with standard pistons with new rings - waiting for confirmation at present - but with the price of just new rings, VAT and postage, it adds up to almost the price of pistons and all.

[DanMi]

Plus I would rather pay a few quid more for NOS quality, even if you just use the rings and swop them to the existing pistons. They are also PEP so have a slight lip on the upper ring so are designed not to break on the slight ridge from bore wear, though I would have hat honed out anyway

[Pete Lewis]

step rings used to be the normal when re ringing was a common game , i doubt if honing would remove the  ridge in the bore 

pete

 

[Nick Jones]

Split skirt and 4 rings is archaic.  They went away from the 4th ring due to the considerable extra drag they cause, sapping power, and increasing fuel consumption.  If you do use those pistons, at least leave the 4th ring off!

Nick

[Colin Lindsay]

On 12/01/2020 at 16:47, DanMi said:

press fit solid skirt   18261 these are rare

He has 18262 for the larger engines:

https://www.ebay.co.uk/itm/Triumph-Spitfire-Std-Pistons-1296cc1967-Press-Fit-Pin-Fitting/202790838181?hash=item2f37469fa5:g:swsAAOSwlRpZaStD

15 hours ago, Pete Lewis said:

step rings used to be the normal when re ringing was a common game , i doubt if honing would remove the  ridge in the bore 

pete

I've to get the block checked but as I can't lift it at present it's holding things up slightly. It's a very very slight ridge on two pistons only. One local member who checked it told me that back in the day he'd have used step rings; Cords were recommended as they'll seal right to the edge of the lip but are angled so as they're below it. I'll probably end up going for good pistons be they modern or not; those on eBay are a step back. It all comes down to the final cost!

[Pete Lewis]

and they are still about  that surprised me 

http://www.cordsduaflex.com/index.html

pete

[Colin Lindsay]

Not sure which one the Herald fits into these days... stationary, maybe?

CORDS Duaflex supply OEM and OES standard piston ringsets for the 
following applications:-

agricultural
heavy industrial
stationary
commercial
aviation
marine

[JumpingFrog]

FWIW County pistons are actually quite good by most accounts, consistent weights and consistent sizes in my sets. The rings packs they're supplied with are okay too, made by a major manufacturer (Grant).

Probably 4-ring pistons are a hang over from when the SC engine first appeared @ 803cc in the Standard Eight, I'm pretty sure even the 948 only ever had 3-rings.

Can someone shed some light on the reason for standard size replacement sets to exist? I was under the impression that bores should be bored to the size of *each* piston to get correct clearances, and with factory pistons coming in multiple grades, it seems odd to me that you'd be able to just replace these and maintain correct clearances?