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TBI 350, Taper & Out of Bore....


chevy666
02-10-2016, 05:05 AM
Hi!

Iīm about to do a rebuild on my K1500 TBI engine, 5,7 vin K.
Iīve measured the cylinder bores with a bore indicator (with a dial indicator) and iīve noticed that i have some bore, taper and out of round measurments that are out of specs, so with this being a budget rebuild i wanted to check with you guys if you think a boring is needed or if i can get away with these measurements, im thinking of going with a rebuild kit with new pistons etc and do a honing.

Measurment of the worst bores are:
Cylinder 1: Diameter at top 4.0029"
Cylinder 2: Taper 0,0018
Cylinder 3: Diameter at top 4.0035"
Taper 0.0018"
Out of round 0.00276"
Cylinder 4: Diameter at top 4,00315"
Taper 0.00157"
Out of round 0.0024"
Cylinder 5: Diameter at top 4,00315"
Out of round 0.0031"
Cylinder 6: Diameter at top 4,0027"
Taper 0.00118"
Out of round 0.0029"
Cylinder 7: Diameter at top 4,0027"
Cylinder 8: Diameter at top 4,00315"

Haynes says the limits are 0.001" for taper, 0.002" for out of round and bore 4.0025. I would like to get your opinion regarding this due to this being a budget build but if a boring is neccesary the so be it, but i donīt want to spend money at the machine shop if its not needed due to the prices here in sweden...

Thank for all the help i can get!

/Sam

maxwedge
02-10-2016, 08:24 AM
For normal usage, this will not cause issues, after a quick hone you could use .005 over rings and end gap them to spec. Done right should be 30 over but expensive.

Schurkey
02-11-2016, 03:27 AM
I was told--decades ago--that the limit for taper on a "rebuild it and sell it" job is .007. I would expect an engine built with with "seven thou" of taper to be a time-bomb in terms of oil consumption, and with a possibility of piston knock and reduced power.

I'd expect those cylinders when new were 4.000". You're showing that the bore wear at the tops of the cylinders is as much as .035. To me, that's your cylinder taper (bellmouth). About half of the "worst acceptable" figure as I understood it.

Yeah, you could put it together. It should work for awhile. Taper and out-of-round is hard on rings and ring lands. I'm not saying I recommend it, and I can't figure out why you'd spend the money to put new pistons into worn bores. Assure that you have adequate ring end-gap in the least-worn part of the bore.

maxwedge
02-11-2016, 08:44 AM
As read it is .0035, not .035, no? Big difference.

j cAT
02-11-2016, 11:33 AM
This why I do not recommend the re-build of a very common engine that has high miles and wear. costs too much and the end result is not all that great for the cash you dump into it. if this was some odd ball engine/hard to find and restore to a vehicle of good resale , that would be then a machine shop and all new parts for a proper reconstruction . probably cheaper to have a 350 shipped to EU.

chevy666
02-11-2016, 12:43 PM
Hi guys and thanks for your replies and input, I'm struggling with choosing in what direction to go with this build, the thing is that it's a 350 Tbi engine that won't see faster speeds than 60 mph so how much should you invest in time in money for it to be worth it. Sure if it was a big block for an more rare car and I had more money I would go all the way with leaving the block and heads at the machine shop for work and inspection.
But a rebuild kit that I have been looking at is a kit from EngineTech: http://m.ebay.com/itm/Chevy-350-5-7-Truck-87-92-Rebuild-Kit-/300833831766?nav=SEARCH

Comes with all needed gaskets, bearings and even Pistons and oversized parts of needed (one of my oem pistons is missing a peace from the skirt therefore I'm thought it would be the same in changing the Pistons) and this kit is delivered to Sweden for approx 375$, the macine shop wants 400$ for boring the block and another 400$ for checking and leveling the heads, so to go all the way will make this simple tbi engine a very expensive engine and at the same time I think it's hard to make this engine with the tbi and all to produce any heavy hp numbers...

The odd thing is when I measure the bores the "worst" out of round is found in the middle of the bore, it's like it's almost wider in the middle of bore than at the top... Is this common that wear can be more excessive in the middle of the bore?

I wanted your input in this matter because you more than likely have more experience in these engines and what is possible and don't than any of the guys I've checked with here in Sweden, but I don't want to assemble the engine and all just to have it break down again after a short while so maybe It's best to put this project back on the shelf... It's funny, I've owned this truck for 8 years now and it's been in the garage for 7 of them waiting for something to happen with the engine... But with a house and three kids have come between me and the engine

maxwedge
02-11-2016, 04:27 PM
You are over analyzing the type of bore wear, not an issue, usually the greatest wear point is at top of the bore where the rings exert the most pressure on the walls. That said, rod angulaity, piston skirt design also enter the mix, every engine will show somewhat different wear patterns, go .030 and do it right. I assume in Sweden crate engines are less common and more expensive, no? Make sure the crank journals do not need resizing also.

Schurkey
02-11-2016, 08:27 PM
You're showing that the bore wear at the tops of the cylinders is as much as .035. To me, that's your cylinder taper (bellmouth). About half of the "worst acceptable" figure as I understood it.

As read it is .0035, not .035, no? Big difference.
Yup, I forgot to add another "zero". But as explained in the text, he has .0035 taper/bellmouth, which is about half of what I've considered to be the "worst acceptable" amount of .007.

It appears that the cylinder walls are wavy--worn in the middle, worn at the tops, less worn in between, and at the bottoms. None of that wear is good.

$400 to bore eight cylinders is $50 per hole, and my expectation is that the shop will not be using a torque plate when honing the fresh-bored cylinders. Fukkin' outrageous in the USA...but I don't know about Sweden. Have you considered showing up at the machine shop with a liter of Akvavit and seeing if they'll treat you better?

Were there any signs of cylinder head problems? How many miles are on them? $400 to "check and level" the heads may or may not be fukkin' outrageous. I assume this means they'll disassemble and inspect the valves, valve guides, valve seats, springs and retainers, and plane the gasket surface(s). Then--assuming the parts are OK, reassemble with fresh valve stem seals. I think you should be prepared for the inevitable valve face and seat reconditioning, along with bronze liners in the guides. I suppose this will cost extra. Consider having them vacuum-test the valve face/valve seat sealing after removing the valve springs and inspecting for guide wear. Hopefully you can get by without reconditioning the heads beyond installing fresh valve stem seals.

chevy666
02-12-2016, 03:06 AM
Yeah $50/hole is quite expensive and thats without honing, thats another extra $20/hole.... Thatīs the prices here in sweden but then the machine shops mostly deal with straight 4 & 6 cylinder blocks... If Akvavit would help then i would bring a hole box, but then maybe im left with worse wavy bores :)

No i didnt have any signs of cylinder head problems, more lifter issues or oil pump issues i would say. Previous owner "never" changed oil which resulted in terrible sludge that i found out a while after i bought the truck... I belive this sludge clogged up the pump & oil passages so the truck ran terribly at the end.
I have disassembled the valves on the head and the seats need a recond, and who knows what other things they find that need work on these simple 193 heads...

Im thinking of saving up and going with the reboring, if i put in new pistons, rings etc and then only to have it running terrible or seizing up again then im back to square one... Do you think a .02 bore will be enough or is .03 a must?
Do you have any experience in TBI units? Do you think the reboring will affect the TBI unit and maybe reprograming of the chip is needed?

maxwedge
02-12-2016, 08:14 AM
No issue with the tbi set and programming with a stock rebuild. .030 is the most common overbore on these engines. For a everyday driver a torque plate hone is not usually done.

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