Piston direction ?

[sleek lemur]

Hi all,

Assembling the pistons and rods in my B18A rebuild. The new pistons have a small notch on the upper face, which could face the rear or front of the cylinder. Apart from this notch, the pistons look symmetrical. Which way round should they go ?

Thanks as always.

SL

[Derek UK]

https://www.youtube.com/watch?v=D-JVOhefUcQ

From about 15 minutes in. Pistons and rods have to fit together the right way round.

[sleek lemur]

Thanks Derek. That video has been by Bible!

However the pistons that Rob uses in the video have an X mark which aligns with the number on the rod. My pistons have no such mark, but a notch in the crown, which could be oriented either front or rear of the cylinder. In fact I just found this, which shows that the notch should face forward.

http://212.247.61.152/EU/ZF0001_bild...%20the%20locks.

Before I go ahead, I think I'll just see what our fellow forumers have to say!

[sleek lemur]

Brookhouse advise that the notch goes to the front.

BTW, remember that the number stamp on the conrods goes to the opposite side to the camshaft.

[142 Guy]

The 1971 service manual for the B20 confirms that the slots / notch faces forward.

Remember to check the ring end gaps by inserting the rings into the cylinder bore and measuring the gap with a feeler gauge. Use a piston inserted upside down and pushed up against the ring to 'square up' the ring in the bore. The 1971 service manual says 0.016 - 0.022" for the end gaps on the B20. Check the SM for the correct gap for the B18. I had to file a couple of my ring ends to get them 'in spec'.

I can't remember whether you did a rebore. If you didn't rebore check the end gap at the bottom dead center position where wear on the cylinder walls should be the lowest. Remember to break the ridge on the top of the cylinders if you didn't do a rebore.

Remember to offset the ring gaps when installing the piston and rings. The B20 service manual just says "turn the rings so that their gaps are not opposite one another". I have never been quite sure what "opposite one another" means - 180 deg apart? I thing I installed mine with the gaps spaced 120 deg. Some OEMs specify where the gaps on each ring are to be positioned in the cylinders. The Volvo service manual does not. The Volvo service manual says that the top compression ring on the B20 is chrome. I don't remember that; but, it has been 9 years since I did my rebuild so those details may be lost in memory fog. If you have a chrome compression ring in your ring set, make sure it is installed in the correct position.

Re the note about fitting the connecting rod with the number stamp opposite the camshaft. I have a similar notation scribbled in my service manual about the marks on the connecting rod facing away from the camshaft. My notation just says marks so I don't know whether they are numbers or marks - maybe they changed during the production run (B18 vs B20?). The connecting rod and the end cap both have 'marks / numbers' so be sure that they match up and face away from the camshaft.

[sleek lemur]

Thanks 142. Really interesting. there was a significant lip on the bores, so had 30 thou rebore. The machine shop wanted to see the pistons as well.

I settled for 120 Deg offset on the rings.

Crank was still within tolerance. 0nly 1/2 thou wear, which is amazing, as the lump when bought was in a very sorry date.

Pistons installed safely and everything still turns.

Which is nice.

Onward!

[sleek lemur]

Another question. Would one usually replace the nuts for the big end bearing caps?

[sleek lemur]

Another question. Would one usually replace the nuts for the big end bearing caps?

[Army]

Originally Posted by sleek lemur

Another question. Would one usually replace the nuts for the big end bearing caps?

On the whole "I would" for most engines - having never delved deeply into the Volvo B18/20 engines I can't say I've ever read what the workshop manual says however...

{I must say I'm really glad some joker didn't answer the title of this thread by saying the piston direction is either up or down the cylinder bore!}

[Derek UK]

You might also consider measuring the length of the big end bolts to see if they are within spec. You might find one or two that have stretched.

Not listed by Brookhouse so probably not normally changed.