Cylinder bore question

[Morris]

Well, I bought a set of pistons on eBay. I have a choice of sizes I can get. Originally, I was not planning on boring as my cylinders measure out as stock. But since I have deglazed the walls, I have discovered long scratches (perpindicular to the crank of course) on the walls of the cylinders.

My question is, can I safely make a guess of how much of an over size I need to get, or must I wait till the machine shop is done before I order my pistons?

 

[jcatnite]

You really need to have a machine shop measure the cylinders in regards to the depth of the scratches as well as any ovaling that might have occured in the bore. You can do this yourself if you have the right equipment. The scratches are most likely not deeper than .010" so usually the "out of roundness" correction will take care of the scoring as well...but not always. After you come up with a good number for boring, then order your pistons for that oversize. When you get the pistons take them to the machine shop and they will bore the cylinders to fit the pistons. (this will take into account the variations in manufacturing tolerances of the pistons) so that you have the absolute best fit. I know this isn't the fastest way or most convenient answer but it will give you the best results. Should probably let the machine shop take a look at the rods as well. There might be some wear in the wrist pin area that might have to be addressed. What about your crankshaft? Are you going to have to have it ground or is it in good shape? Flywheel? I know you are on a budget (and so am I bud) but a little exta effort here will directly impact the results of your rebuild in both power and longevity. How is the head? Take a look at each valve and seat as well as the condition of the valve guides. Most of the cost in these things comes from the cost of the parts which we have a good source for (sometimes better than the machine shop might have on older cars such as ours.
JC

 

[jlaird]

Ask the shop, they can mic. and tell you for sure. No place for guesses here as this rebuild will last forever.

 

[Morris]

Soooo, maybe I should just order the largest cylinders (.04 over) and drop them off with my block. Can anyone think of a reason not to got this route?

 

[jlaird]

.040 over sounds good to me.

 

[jcatnite]

Only problem is that you don't leave much room to bore the block again should any problems arise. Unless I'm shooting for larger displacement to marry a different cam and possibly stroke with, I always try to keep the bore as close to original as possible to give myself some wiggle room. Otherwise, I say go for it.
JC

 

[77_MG_Midget]

Personally, i would only recommend boring the minimum required. Mine had to be taken .020 over standard. Although on a budget, don't cut corners on machine work. I had my block/cylinder head dipped, the block bored, crank cut .010 and balanced, pistons and wrist pins replaced, rods and crank magnifluxed, valve seats replaced, all valves 3 way cut, new valve guides, head fitted with valve seals (which they didn't have originally), block decked and cylinder head shaved. Finally, had the machine shop put the head back together (much easier for them). Total cost was $550.00 out the door.

Keep in mind, the head work itself was $250.00. so, if you don't need your head rebuilt, would be about a $300.00 job or so for all block/rod/crank work. To save a little money, I decided to reassemble the bottom end myself. But, I have no doubt now that I have a motor that will last at least another 100,000 miles (i sure hope... lol).

Just my 2 cents.

 

[jollyroger]

Let the machinist tell you what size piston you need. Then order them. It doesn't take that long and that way you do the job the right way.

 

[Morris]

Too late for that one. Doh!

I've go to work on this patience thing. It's just that the weather is so nice now and it is going to be a looooong hot summer.

You know what I am talking about, Jolly.

 

[jollyroger]

I like the HOT summers. The hotter the better. Nothing better than 110 degrees and 90% humidity. Did I say I also hate snow and the related stuff.

 

[DrEntropy]

AWRIGHT!!! That's JUST the right attitude!

As for bore: I too am of the "minimalist" persuasion. Cut as little out of the poor dear as necessary. YOU may not plan on another rebuild, but there MAY be a *next* owner and they'd be at a disadvantage if it were max'd out now just for convenience sake. And if (heaven forbid) something goes awry internally, you still have some block left to do it over.

 

[jlaird]

I'm with Jolly. Give me summers.

Can always sleave Doc.

 

[Morris]

The wonderful man known as JollyRoger has offered me a spare 1500. So I have a back up.

I prefer the heat to the cold as well— but I prefer sunny, dry, moderate temperature spring to all else.

 

[DrEntropy]

Sleeving is okay, but ~preservation~ is more desireable in my opinion. I've had many a B engine sleeved, but I just think if it's at standard bore now, it'd be a shame to hog it to 0.040" over for no good reason. just my two cents' worth.

EDIT: It ~JUST~ hit me!! It's a 1500 *Triumph* engine!! Go-on then, BORE IT OUT!!! /ubbthreads/images/graemlins/jester.gif /ubbthreads/images/graemlins/devilgrin.gif /ubbthreads/images/graemlins/hammer.gif

 

[jlaird]

LOL