23 replies to this topic

[BiBiBiB]

Dear all,

I’m sadly having to deal with a bad situation. Advice and information appreciated.

Its regarding a fully restored and rebuilt MK5 which I bought for quite a large sum less than a year ago from a reputable dealer. However, there are now serious doubts on the quality of the engine rebuilt. Current engine is written off, which is barely 10k km after the rebuild.

Original 1275cc SPI engine was bored out to a maximum of 1398cc; fast kent cam and weber carb.
It never felt as fast as it should. I drove it once two or three weeks and mostly let it sit in de dry warm garage till this summer. Plan was to have the weber setup professionally; and to replace exhaust and manifold in order to get power up to expected levels.

However, it turns out the issue is much larger: there next to no compression in nr. 3 cylinders. Major damage on sidewall is the cause (nr. 1 and 2 have minor damage). Enclosed pictures. Feeling pretty screwed as you can well imagine.

So far the assumptions is either that the damage was done due to a chunk of carbon that got loose from the head; or shabby pistons.

• As it turns out, the head was not altered to fit the conversion from SPI to Carb. Red flag. May be cause of extensive carbon build-up in head. What do you think?
• The boring is not your typical 1380 but 1398. My mechanic stated in his report that the pistons sit too loose. See pictures. He however could not tell me what the correct size should or would have been, for a 1398 boring. I want to establish if the correct piston size was used. Can someone provide me with this information?

Thanks in advance.

Attached Files

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•  IMG-20220621-WA0000.jpg   65.87K   16 downloads

Edited by BiBiBiB, 27 June 2022 - 10:42 AM.

[sonscar]

In my inexperienced view it looks like a ring has broken.Personally when buying I like the I have never touched anything view and expect everything to be junk.Commiserations with your experience.Steve..

[cal844]

That block is saveable but needs sleeved back to 1275 or 1293. This needs done by professional machinists

[KTS]

a rebore to 1380 would usually mean the bores being taken out to 73.5mm, which is about the diameter of the firecontrol ring built into the head gasket.

 

the first photo shows what look like carbon deposits on the block face, so i would question whether or not the block has been substantially overbored; take the block to a machine shop and get them to accurately measure the bores.  only then will you know what your options are

[nicklouse]

 

As it turns out, the head was not altered to fit the conversion from SPI to Carb. Red flag.

 

Sorry what does this mean? Or what are you expecting?

 

 

Plan was to have the weber setup professionally

 

So it was never actually set up?

[mini13]

Important point here,  the block should be bored to suit the pistons.

 

Generally the pistons are quoted as 74mm for 1400cc, but between different manufacturers or even batches there may be size differences, you then bore and hone the block to give the correct clearance, normally 2-3 thou at the "A" dimension of the piston. Also pistons are tapered and barrel shaped, so when they are at operating temperature they are the right shape for the bore.

 

second important point, the piston ring gaps must be right, other wise when they expand the ring may run out of clearance, and damage the bore and piston or break up

 

Edited by mini13, 27 June 2022 - 10:45 AM.

[BiBiBiB]

Thanks all.  

 

Indeed the weber was never setup properly, as it turns out. I bought the car from a very repeatable Lotus dealer in NL. They got the car from a professional old timer specialist. Or so I was told.... the seller seems reasonable so far and we're going to talk, however, I want to know exactly what I got myself into, i.e. what was the quality or the rebuild. 

 

The inspection work was done by a mechanic I trust. My mechanic noted in his report that the engine started life as a 1.3 SPI and was later converted to a carb unit, along with the huge Weber. In The head of the engine was left stock however.  In his opinion, the head should have been rebuild to compliment the weber and carb build.

 

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. 

[PoolGuy]

 

 

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.

Edited by PoolGuy, 27 June 2022 - 12:38 PM.

[BiBiBiB]

thanks. That helps.

Finally, what is generally speaking the correct clearance between the piston and wall? .002?

[PoolGuy]

thanks. That helps.

Finally, what is generally speaking the correct clearance between the piston and wall? .002?

It really depends on the piston manufacturers figures. But that's the sort of figure that's used for Omega cast pistons, maybe a little less for a road engine and more for a forced induction car. But you really do need to take the manufacturers figures as I'm just generalising.

[BiBiBiB]

I inspected the engine myself. There was a minimum of 0.5mm of clearance, on average ......  

[sonscar]

When sizing pistons I thought you measured the skirt?Could very easily be wrong.I think that running too rich and not hard enough at break in has damaged the bores.Steve..

[ACDodd]

Bores look glazed and washed out to me.

Ac

[weef]

The lack of any carbon build up around the inlet valves does not look too good either, overfueling???.

[mini13]

as per my previous post, these a specific place to measure the piston the "A" measurement. right at the bottom of the piston at 90 degrees to the pin, you cant go by the top of the piston, it will be hugely different.

I inspected the engine myself. There was a minimum of 0.5mm of clearance, on average ......