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Engine Fail 10K Km After Rebuild. Q Re. Correct Piston Size For 1398Cc?


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#16 Spider

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Posted 27 June 2022 - 08:19 PM

 

 

 

The car was very explicitly sold as a) fully restored and rebuild; b)1398cc. My guess is that the pistons have to be a minimum of 73.50. Infact, that already is too small for the 1398cc bore.

 

I have yet to see the opened engine myself. Going to do that today and take measurements. 

1398 is 74mm bore and 81.28mm stroke.

 

 

Like all of us, I can only go off the photos here, but the bores to me don't appear that big.

The bores look like every other I've seen when a Weber has been fitted - save for the heavy scoring - that is well washed. Just my view, but they aren't a suitable street carb.



#17 Cooperman

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Posted 27 June 2022 - 10:48 PM

It is obvious that you will require a rebuild which will mean sleeving the bores. Best thing to do is go back to 1275 cc.
The problem with engines already at more than normal over-bore sizes is that they cannot be simply rebored.
You may be able to find some sleeves to fit, but if not you will need to get special ones made to fit. A better/cheaper way may be to find a block at no more than plus 40 thou over standard. The sidewall thickness of your block will be very thin and boring further for sleeves could break through into the water jacket.

#18 Earwax

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Posted 28 June 2022 - 09:26 AM

BiBiBiB .... it is probably worth getting the jetting/choke info from the weber in question ( I assume a 45?) 

 

I am a bit confused ... you say you ran it two or three times for putting away and have only now brought it back out ( which seem like very few real kilometres)  and you also say engine written off after 10k km ,,, is that 10 000km?

 

Probably not what you want to hear but having 10 000km worth of possibly extremely rich running and significant bore wash isn't a good look or feel, especially when you felt it wasn't going right power wise. ( I don't know how long it takes for bore wash to occur but there is a good reason a number of people basically take the car straight from heat cycling and start up to the dyno/rolling road)

 

I have a 1360 road motor, but it has head and valve improvements over standard, and i have had it running really well on a weber 45 on the track, but for street use it started with twin HS4 SUs and now currently runs a single HS6 ( a Hif44 would have been good too).  Both the SU setup runs well. 

 

I have found it much harder to guess a safe starting jetting on webers (others with more knowledge can offer advice on the webers, whereas i could confidently say twin HS4s running #6 needles or equivalent  or a HS6 or HIF44 with standard needle will safely start you up and get you to a rolling road or at least someone with a wideband AFR meter.

 

and finally - it would be prudent to look at the whole unit now - that way you will know the gearset used the diff ratio, whether you have a centre oil pickup etc and also it is much less problematic seeing and replacing a worn diff pin, or get a thread helicoiled now rather than roadside somewhere down the way....... 

 

Best of luck



#19 Cooperman

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Posted 28 June 2022 - 11:36 AM

https://www.med-engi...cylinder-liners

 

These are what you will need and they will enable you to go back to 1275 cc with 3 more re-bores still available.



#20 Maccmike8

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Posted 28 June 2022 - 04:04 PM

Hopefully you will get some or all the repair bill paid by the seller and to your specs, at least then you know exactly what the build is. And get it set up once rebuilt. Best of luck.



#21 DomCr250

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Posted 29 June 2022 - 04:21 PM

 

 

 

 

The car was very explicitly sold as a) fully restored and rebuild; b)1398cc. My guess is that the pistons have to be a minimum of 73.50. Infact, that already is too small for the 1398cc bore.

 

I have yet to see the opened engine myself. Going to do that today and take measurements. 

1398 is 74mm bore and 81.28mm stroke.

 

 

Like all of us, I can only go off the photos here, but the bores to me don't appear that big.

The bores look like every other I've seen when a Weber has been fitted - save for the heavy scoring - that is well washed. Just my view, but they aren't a suitable street carb.

 

Could not agree more, twin chokes are more of a fashion statement than a performance upgrade on a roadcar.

 

74mm 1400's were popular in the late 70's and 80's in the UK, but I seem to remember wall thickness and head gaskets causing reliability problems, so the 1380's took over.

 

All engine builders can sometimes make mistakes - they are only human after all.

 

Have you measured the valve sizes and made 100% sure the heads not modded?  Some of the best work is very had to spot


Edited by DomCr250, 29 June 2022 - 04:31 PM.


#22 Turbo Phil

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Posted 29 June 2022 - 06:17 PM

The chambers are standard as are the valve sizes, 33/29mm. Even if there were other work done to the head it would be far from optimum for a big bore motor.

Phil.

#23 BiBiBiB

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Posted 02 July 2022 - 02:50 PM

Update: the seller and I came to an agreement. Decided to replace the entire engine with a newly revised A+ and Hif44.

#24 Spider

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Posted 02 July 2022 - 08:10 PM

Update: the seller and I came to an agreement. Decided to replace the entire engine with a newly revised A+ and Hif44.

 

That was very decent of them as usually, it's 'buyer beware'.






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