Hi All,

I am building a Supercharged 1275 +60 and have just done the dry build. I have found the piston sits 1.52mm down the bore and has a dish of 11cc. This is giving me a compression ratio of anywhere between 7 and 9 to 1 depending on which calculator I use with most results in the 7's. I am aiming for 8.5:1 . I have tried working it out manually but maths was never a strong point so am struggling to get an accurate result.

The pistons I am currently using are NOS Mahle with a compression height of 37.13mm or 1.462in.

I don't want to skim the deck any further and am considering changing the pistons.

Does anyone have any other options or any suggestions which pistons to go for? I don't want forged due to the cost.

Thanks

I had both Russell Engineering and Hypatec when my motor had a blower, both made the required squish and bang. GR machined the dish in the RE pistons for me

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did I tell you that I won a trophy?

If you want someone to check your calculations, they will need the chamber cc and possibly gasket being used.

Thanks.

I will be using the BK450 gasket and a 26cc chamber.

Your published figures equate to 8.2:1 CR
head 26.0cc
bk450 3.0cc
dish 11.0cc
deck 6.0cc (1cc per .010" bore)
total 46.0cc
1330 332.5cc per cyl
total 378.5cc
cr 8.2:1 378.5/46.0

hope this helps
For 8.5:1 you could take .020" off head

I am using stock Mahle pistons in a 1310 (1275LS engine). They have a slight dish. I am running about 14-15psi with no worries.
BK450 gasket, stock head (12g940 not shimmed).
Not sure what CR but it does the trick. I wouldn't worry too much as long as it in the ballpark. Just need to adjust timing curve to suit.

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1310 SC 1969 Morris Deluxe - 15psi boost
1293 1968 Morris Deluxe Miglia - 45 Weber
HSV Maloo Z Series - Comp Cam - 300rwkw
Ford DF LTD - 5Ltr

Thanks for the responses.

I am thinking I might settle for the 8.2:1 and if I need to I can skim the head later.

Another issue I have just found when putting on the timing chain. The chain appears too long. I have checked the part numbers on the box which are correct. I can think of 1 of 2 things causing it. 1- Incorrect chain in the box or 2- I have muffed something up big time. I have contacted the supplier, just awaiting a response.

Can someone please tell me that it is the chain and not me...

Count the links, should be 52.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I was interested so I counted the dots/pins from the photo and got 54 if that was what was supposed to be counted?

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1972 Leyland Clubman, 4EFTE 1330cc Turbo, 220Hp on 17psi
(1/4 mile: 13.8s @108mph @168Hp)

Yes.
So it's 2 links (actually are half links) too long.
Can cut it and fit a joining link.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I got a call from the supplier today. They had a batch that had 54 instead of 52 links awhile back. I have now removed the 2 links and fits perfectly.

Thanks for the advice

I have a timing cover with an external oil seal. How well do they work or should I give it a miss?

Thanks

Hi

I am sorting out my primary gear now. I need to get a thrust washer so how can I work out which size to get. I don’t really want to go trial and error if it can be avoided. I don’t have a 1275 one to try. I have a new minispares gear and a backing ring and C clip. Are the backing ring and C clip the same for small and large bore?

Thanks

Yes, the thrust washer is not though.

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1963 Morris 850 Smoke Grey
1963 Morris 850 Shadow Blue
1965 Morris Mini Smooth Van
1966 Morris Mini Van
1969 Morris Mini Deluxe Resto
5/72 Clubman Gt