19 replies to this topic

[Dan16v]

Model:1380cc A-plus
Year:
Description of problem (please be as in depth as possible):

I’m after a bit of advice about score marks in the main piston bores.

I am looking at buying a second-hand 1380cc engine from a friend which has done about 2 to 3k miles, it had been sat for about two years prior to being started, but we put plenty of oil down the bores and left it a few days before turning it over, first without the plugs and then put the plugs back it, it fired first time and all seemed fine.

We did a compression test, although a bit high (near 200 psi, which is probably to do with the accuracy of the gauge) they were all within 5 psi of each other.

After it burnt off all the oil we put down the bores, there was no visible signs of smoking at all.

We took the head off to check the bores before I buy it, and there is a small score mark on number 4 cylinder, its about 2 inches long and you can just feel it with your finger nail. There are two others about 10mm either side of the main one, but you cant feel them. In each cylinder there is also a ¾ inch wide shinny strip up the bore where the hone marks have disappeared, they are all in the same place at the back of the bore.

The question is, is this normal and will it run ok with a small score mark and are the shiny strips at the back of the bore normal?

Sorry for the long post!

Thanks, Dan

[Jordie]

Guidegeon pins loose?

Happened to me on the turbo engine. Either incorrect fitting of the pins (ie. conrod warmed up too much) or extreme heat during use, can loosen them.

They are interference fit. So no securing pins/clips or bushes at the ends.

If the pins are at fault and eventually dig a deeper score in the block, they will most likely damage the pistons aswell. Ring damage as expected and also the hole in which the pin sits, becomes ovaled and the pin will move up and down during use.

Strip it down and have a look. Scores in the block render that 1380 u/s now anyway.

Edit. Just read - back of bore? that might make the above information a total guess as the pins run from left to right as u stand infront of the engine. I should read better before replying.

Any pics?

[Dan16v]

Guidegeon pins loose?

Happened to me on the turbo engine. Either incorrect fitting of the pins (ie. conrod warmed up too much) or extreme heat during use, can loosen them.

They are interference fit. So no securing pins/clips or bushes at the ends.

If the pins are at fault and eventually dig a deeper score in the block, they will most likely damage the pistons aswell. Ring damage as expected and also the hole in which the pin sits, becomes ovaled and the pin will move up and down during use.

Strip it down and have a look. Scores in the block render that 1380 u/s now anyway.

Edit. Just read - back of bore? that might make the above information a total guess as the pins run from left to right as u stand infront of the engine. I should read better before replying.

Any pics?

I didnt get any pictures im afraid

Yes, the shiny section is at the back of the bore, you cant feel a ridge though, its just looked a bit more glazed than the rest of the bore that still has all the hone marks. And its the same on all 4 cylinders.

Is it the general consensus that any kind of score make that you can feel with your finger nail means the block is scrap?

[stardude]

could always bore it out to 74mm and get pistons from jonspeed. 1399 i think??

[Dan16v]

could always bore it out to 74mm and get pistons from jonspeed. 1399 i think??

Its finding the time to do it, I was trying to get a engine to drop straight in, and it depends on how deep the score mark is to determine if there is enough metail there to bore it out to 74mm, as your only taking 0.25mm of metal to get 0.5mm on the diameter

[MRA]

you can feel 1/2 of 1 thousandths of an inch with your finger nail........ if it didn't smoke, unless its piston ring damage, it may never give you any trouble.... it depends on the price and if you are willing to take a chance..... if it was for a customer I wouldn't even consider sending it out. however you have heard it running and seen no smoke so its a fair chance that it would be good enough for some time....

[Dan16v]

you can feel 1/2 of 1 thousandths of an inch with your finger nail........ if it didn't smoke, unless its piston ring damage, it may never give you any trouble.... it depends on the price and if you are willing to take a chance..... if it was for a customer I wouldn't even consider sending it out. however you have heard it running and seen no smoke so its a fair chance that it would be good enough for some time....

Thanks mra-minis, its only a very slight mark, have you ever seen the shiny verticle stips at the back of the bore that I spoke about?

Well, its £500 with a newly rebuilt gearbox and had all new bearings and bits 2k miles ago

[stardude]

how big is this strip??

oopsi should read better

Edited by stardude, 02 May 2009 - 03:10 PM.

[stardude]

what it might be is a steel insert used during the casting of the block, as described in vizards book on page 406

if that is what it is then its no cause for alarm

[MRA]

steel cores are usually between the bores...

[Dan16v]

what it might be is a steel insert used during the casting of the block, as described in vizards book on page 406

if that is what it is then its no cause for alarm

I think thats just a insert that apears half way up the bore isnt it? this is similar in width, but goes down about two inches starting roughly 3/4 of an inch from the top of the bore. Its shiny were as the rest of the bore still has very visable hone marks

[stardude]

ahh ok ignore me then

[ANON]

In each cylinder there is also a ¾ inch wide shinny strip up the bore where the hone marks have disappeared, they are all in the same place at the back of the bore.

have seen this a couple of times on blocks that have been off set bored towards the front of the block. been caused by the pistons running slightly forward of the centre of the crank.

[Dan16v]

In each cylinder there is also a ¾ inch wide shinny strip up the bore where the hone marks have disappeared, they are all in the same place at the back of the bore.

have seen this a couple of times on blocks that have been off set bored towards the front of the block. been caused by the pistons running slightly forward of the centre of the crank.

Does that usualy lead to it wearing out on that side of the bore over time?

[ANON]

don't know for certain, but it was the only thing we could think of that the ones i looked at had in common.
mate of mine has off set bored loads of mini blocks over the years, he only off sets to the sides not to the front. he was saying about having problems with the pistons not running true to the crank when you off set to the front of the block.

don't know if this is the case with yours but it does sound similar to the ones i worked on.

have you got a pic of one of the bores ?