engine rebuild advice - pictures attached

[bnamunds]

I'm rebuilding my 1988 petrol 2.5L motor, the motor has just over 60,000 original miles and I'm looking for some advice whilst rebuilding it, sorry for the multi-part question but I know there are much smarter engine people out there than I.

a. Is there an easy way to determine if I should to replace the piston rings?  The pistons run smooth in the cylinders, and the cylinder walls are smooth, and flat to the touch. At the top of the stroke, there is just a barely perceptible amount of lateral play in the cylinder when you try to wiggle it side-to-side.  I attached pictures of the cylinders for reference.

b. If I do need to replace the rings, must I then have the cylinders re-bored .01 or .02 over and then get new oversize pistons and rings?  Or can I just replace the rings on the existing pistons?

c. When I'm in there doing the rings, is it always a good idea to put in new con rod bearing shells too? 

d. Any other misc advice?

Thanks mates..this forum is wonderful

[Bowie69]

The bores look pretty polished, i would invest in a dial bore gauge and inspect them properly at 3 points down the bores for wear and ovality etc.

New pistons and rings go together, if rings are worn, pistons are very likely done for as well.

Unless the bearings are spotlessly new with no wear at all, always replace imho.

 

[Les Henson]

I'd be concerned about that vertical score as well.

 

 

Les

[Bowie69]

Oh, missed that first time round

[monkie]

Just as Bowie69 says, you really need to take the pistons out and measure the bores carefully and corectly using one of these:

http://www.ebay.co.uk/itm/Metric-Dial-Bore-Gauge-50-160mm-Cylinder-Internal-Bore-Measuring-Engine-Gage-/252741792846?hash=item3ad895b44e:g:X-YAAOSw4DJYiifu

you will also need these for other measurements and to zero the bore gauge:

http://www.ebay.co.uk/itm/4pc-Micrometer-Set-External-Outer-Metric-measuring-0-to-100mm-with-Ratchet-Stop-/152244092036?hash=item2372747c84:g:jCoAAOSwAuZX3A-S

You need to find out how much the bore has worn and how it has worn (out of round and taper). These figures compared with the tolerances in the workshop manual will answer your question. If it is in tolerance then lightly hone the bores to make a cross hatch pattern for the new rings to bed in. If it is out of tolerance then you will have to take the block to an engineering shop and get it bored oversize and have oversize rings and pistons fitted.

For the cost of bearing shells, I would just renew them anyway if you have gone to the trouble of stripping the engine down, but I would imagine that they will show wear so will have to be renewed. I would also measure the crank journals for wear too using a micrometer. Don't forget to check the end float of the crank too to check if you need an oversize thrust washer fitted. Same goes for the camshaft.

If you don't want to buy the measuring equipment, I'm sure an engineering shop will take the measurements for you for a small charge and then offer you advice.

This link is for motorcycle engines, but I think it explains how to measure bores really well:

.http://www.realclassic.co.uk/techfiles/tech05031600.html

HTH

[cackshifter]

Or just save money on the measuring kit - if you are going to buy new pistons and rings, just grasp the nettle and rebore anyway, then you know you are off to a clean start - I don't like the look of the score either. Replace all bearings and oil pump while you can, but before doing that check crank for ovality & scoring- check existing shells in case you are already undersize. Short term it might hurt a bit more, but then you know it's good 

[Les Henson]

I agree. If the current pistons are standard, then buy maximum oversize and get the bores matched to them. With care, the resulting engine will outlast you  The block will have to be totally stripped for a re-bore, so I suggest you go for a full rebuild/ restoration. All being well, you will be installing a brand new engine. It is well worth it and I speak from experience.

 

 

Les.

[bnamunds]

Thank you gentlemen..I think I shall go with the rebore and total rebuild.  Here's another dumb question, I'm looking at these pistons from Paddocks, "Piston assy with rings - 040 o/s - 2.5 Petrol" and interpret that to mean they are 0.040mm oversize, so I should tell my machinist to rebore at standard bore size plus 0.040mm correct?

[monkie]

040 is in inches. It equates to 1mm in sensible units

My view is that I wouldn't buy any pistons or other parts until you have consulted your engineering shop first. It may not be necessary to go that far as you can still see the cross hatch on your bores from the pictures. It will depend on the measurements taken as described above as well as how bad any scoring is. They will be able to advise you on the best option after assessing the bores in detail.

There are lots of measurements on many different parts to take to assess wear which is why I think atleast the set of micrometers and feeler gauges are a must in your tool kit. Taking measurements to assess the degree of wear is the most important part of any overhaul proceedure.

However; in the absence of any measuring instruments - take the conrods, crank and the cam shaft along with the block to the engineering shop. It may also be wise to take the head for them to look at too so they can check to see if a skim is necessary and to check the valves / guides for wear.