Hi!

I've taken my 69 chevy 350 to a shop to have it measured. Now I have a little problem.

As far as I know the standard bore for a cylinder would be 4 inches exactly. Well I have 102.14 to 102.25 mm which comes to 4.021 and 4.026 inches. Which piston size would I take? I have been looking at this: http://www.northernautoparts.com/Pro...uctModelId=380

Do I need to calculate some distance between piston and cylinder (can't be that much if any, right?) or should it be as close as possible (and what about rings?)? In the latter case I'd say I need a .030 larger piston and the bore matched to that size, right?

I'm not quite sure what I should have them do to the block in the first place. If I did anything that they offer I'd come to like 4500 bucks for which I might just as well buy a crate engine. But I'd really like to get some inside knowledge here. It's just I'm a real newbie .

Is there something that you seasoned engine rebuilders do in any case while having the engine in pieces? Or is it better to leave it alone unless you really need to do something?

Thanks .

 

Get the block bored out to .030 over. then get the pistons that mention they are for .030 over bores.

 

I'm wondering why the shop that did the measuring didn't recommend something.

.005" variance is huge. I wouldn't keep an engine in that shape together. It needs to be overbored to clean it up and make it consistent.

The bore itself is 4.000", 4.020", 4.030", 4.040", etc., depending upon whether standard bore or overbored to one of the oversize increments. The pistons are slightly under that for the required clearance (even though their size will be listed to those numbers above). The typical approach is to know what oversize you need to go to - that can be measurements by an experienced machinist, or doing the rough bore to a certain point under the final oversize making sure all of the cylinders clean up. Then get the pistons to the overbore size, the machinist will do the final hone to get the proper skirt-to-cylinder clearance.

In your case, it will probably take .040"-over to clean up the cylinders and get the proper honed finish. But, talk to the machine shop to get their take on the situation.

The crank will also most likely need to be turned to the next undersize. If the engine has been rebuilt before, then it's probably at least at .010"-under already. .020"-under is still fine. The rod and main journals don't all have to be the same size, but it's best for all of the rod journals to be the same size, and all of the main journals to be the same size. Conventional wisdom is to not go more than .030"-under.

 

This is a Swiss shop. They don't do chevy engines on a regular basis like most shops probably do in the States. They got the right information about original bore size and were a bit unsure because the actual bore is so much larger.

I'm trying to get a good picture of what needs to be done and whether it makes sense to put that money into the engine at all. Because it will be very hard to find someone who knows this stuff around here.

I'm unsure about the things you said about the crank. How does cylinder diameter affect the crank?

 

The crank doesn't affect the cylinders. I was moving on to other things you will probably have to have the shop do to that block.

I know it isn't easy getting American engines worked on outside of the States.

 

Ah, okay. Well all I know right now is they said the crank looked a-okay. They offered to have it toughened up a bit though I don't know how that process is called in English. In German they call it 'plasmatrieren'. He said if you want to have something with lots of power this could be a good idea but it isn't necessary.

They also said if this was gonna be a race engine they'd advise me to have the crankshaft balanced. But since this is supposed to be 'only' a street engine with some bite and not an actual race engine I don't think I'll take that offer.

I just realised I have no measurements for main and rod bearings. Well, I'll need to give them a call anyway.

What should I doo about valves in your opinion? They look pretty worn and if I need the seats redone, do I have to order larger valves? Since northern doesn't let me choose that size I am unsure how to proceed there.

 

My German is very poor, rusty, and non-technical. It sounds like a surface treatment with a plasma stream. It's probably a good process, but unnecessary in a street engine that gets good oil and regular maintenance.

Are these the '69 heads? Most likely the exhaust seats are "soft" plain cast iron. The exhaust seats and the exhaust valves should be replaced with hardened pieces (unless you can get leaded fuel where you are). Oversize valves typically aren't the approach for worn seats, but if the original intake valves are 1.94 inch or smaller, you could put in 2.02 inch valves and have the seats ground wider to accomodate them. Same with exhaust valves, but if you go with hardened seats, just get 1.60 inch valves and seats. You most likely will need the guides replaced as well.

Use Northern Auto's "customer service" website button to ask about the valves and seats and all.

I must say your English is a lot better than my German or French!!!

 

Well, I have been spending three months in Toronto spicifically for learning the language so I really do hope that it isn't too bad. But the technical aspect of it is rather complicated. I'm new to the whole hobby and due to a lack of similar minded people I have to scrape together my knowledge from foreign sources. That's why I'll probably have to waste lots of time from lots of people on here asking stupid questions .

As far as I know the heads are original. Hmm, thinking about it, I'm not even sure the seats are that worn... I'm pretty damn sure the valves are crap but that doesn't necessarily have to say anything about the seats, right?

Ah well. Christmas. Can't do anything 'till after Christmas anyway. But please do tell, is northern worth my time in the first place or are there better places to get parts?

 

www.summitracing.com , www.jegs.com are very popular around here. The bigger issue would be who ships overseas. I believe they all do. I've dealt with Northern Auto before, as well as Summit and Jegs, but domestically, of course.

A "free" check would be to use each of their customer service request functions asking about what you're doing, making it clear that you are overseas, and see how they respond. The one that gives the best answers is the one to deal with. Price would be secondary.

On older heads, the seats & valves would typically suffer equally. But, the valves you just replace, the seats may or may not clean up before they are too recessed.

By the way, the seats aren't "replaceable". When the cast-in seats wear out, the machine shop cuts them out for a seat "insert" that is slightly larger than the cut made to take it. The seat is frozen to shrink it and the head heated to expand it, the two are slipped together, and when they come to the same temperature, the seat is held in firmly in the head. The final seat grinding is then performed.

 

Hmm... too bad new heads still cost more than the whole work and parts.

As far as I remember the material of the valves looked quite okay. They were just full of... well whatever it was. Oxide with oil or fuel residue thrown in for good measure I'd guess.

I know this will probably be a stupid question but where exactly are the main and rod bearings? I mean the camshaft and the crankshaft both have bearings but I don't know how they're called .

 

The camshaft bearings are one-piece rings and are pressed into the block before the camshaft is installed.

The "main" bearings are half-shells with one half sitting in the block and the other in the main bearing cap. These are what support the crankshaft as it turns. The block halves are installed in the block, the crankshaft is placed in the block on them, the other halves are installed in the bearing caps and the caps are bolted in place on the block.

The rod bearings are half-shells like the main bearings, and go in the connecting rods in the part that connects to the crankshaft. One half is installed in the connecting rod before the piston is put into the cylinder, and when the piston is installed and the rod is down on the crankshaft throw, the cap with its bearing half is bolted onto the connecting rod.

 

Yea, so the rod and main bearings both touch the crankshaft.

$4500 for machine work? I would think if you're getting the machinist there to do the work, it'd be a lot cheaper than buying a new block and getting it shipped there. Most of the stuff you need is small parts, ie bearings, seat inserts, valve guides, etc.

I'd highly recommend you grab a book like david vizards "how to rebuild your small block chevy". It has methods (with pictures), of how to measure valve guide slop, suggested fixes for it, and how its done, etc. (thick bronze guides are a good idea...), and all other fixes for the wear parts.

I'd recommend choosing a high perf shop that carries all the parts you need, so you don't have to place a handful of orders. If you can lump it all together in one shipment you'll save a schwack of coin. A good reason to ask here, "is this list of parts everything i'll need to rebuild my sbc?"

 

five7: Well now that you explain it it all sounds so logical. Why didn't I think of it .

Sonix: that's one reason why I like northern. With a whole set I'm thinking I'll be safer because that stuff is supposed to fit together in the first place.

I'll see that I get the book through Amazon Germany. Shouldn't be a problem.

I guess I'll need an oil punp, a water pump and I'll need to figure out which camshaft to order. That ought to be funny. But before I ask about the camshaft I'll try getting some knowledge in and propose one. I want to learn something here after all . Same goes for the pistons. Shouldn't be too hard to find out what the difference between flattop, dish and dome is.

But I wanted to say thank you to all those who've been helping me so far. It is highly appreciated.