Ford 800 172 engine sleeves--Overbore or Std 3.9?

[fordcomanche]

I've owned my Ford 850 for over 40 years and it was last overhauled in 1970. It ended up getting submerged in a major flood and I plan to remove block, crank, and overhaul everything.

I'm looking at the sleeve/piston kits and see that there is the standard 3.90" bore kit and a 4.0" overbore kit.
Is the difference between these kits just that the 4.0 sleeve is thinner so it has the larger ID but same OD to fit the block, or does the block have to be bored a accept a larger sleeve?

Other than the increase in power with the overbore kit are there any other advantages or disadvantages between the two kits--if the overbore sleeves are just thinner than the 3.9 kit, are they more fragile--is there more chance of distorting or getting them out of round on the install?

Thanks in Advance!
FordComanche

 

[John0829]

I'm looking at the sleeve/piston kits and see that there is the standard 3.90" bore kit and a 4.0" overbore kit.
Is the difference between these kits just that the 4.0 sleeve is thinner so it has the larger ID but same OD to fit the block, or does the block have to be bored a accept a larger sleeve?

You do not have to do anything to the block, you are correct the sleeves are slightly thinner to accommodate the larger pistons and rings.

Other than the increase in power with the overbore kit are there any other advantages or disadvantages between the two kits--if the overbore sleeves are just thinner than the 3.9 kit, are they more fragile--is there more chance of distorting or getting them out of round on the install?

No more of a chance of damage, same PIA as other standard dry sleeve to install

 

[jaxs]

I've owned my Ford 850 for over 40 years and it was last overhauled in 1970. It ended up getting submerged in a major flood and I plan to remove block, crank, and overhaul everything.

I'm looking at the sleeve/piston kits and see that there is the standard 3.90" bore kit and a 4.0" overbore kit.
Is the difference between these kits just that the 4.0 sleeve is thinner so it has the larger ID but same OD to fit the block, or does the block have to be bored a accept a larger sleeve?

Other than the increase in power with the overbore kit are there any other advantages or disadvantages between the two kits--if the overbore sleeves are just thinner than the 3.9 kit, are they more fragile--is there more chance of distorting or getting them out of round on the install?

Thanks in Advance!
FordComanche

What John said is correct but can you post a link to sleeve/piston kits you are looking at? I want to contact them to ask some different questions. Primarly why they go to expense of over-boring sleeves and fitting them with over-size pistons UNLESS they are selling used sleeves. If they are indeed selling used sleeves and since you didn't avail us,I reccomend you go slow and easy,read twice and measure thrice while overhauling your engine. There are many subtle details in shop manual that can spell disaster when overlooked. If it were mine,I'd disassemble,clean,inspect and mic old pistons and sleeves to see if they are within specs to be ringed and reused before ordering new.

 

[fordcomanche]

Hi Guys- I forgot to mention this is 1955 850 with the Gas engine. Due to the flood, the bottom area of the sleeves below the piston stroke has some rust. I can feel some slight wear but I have a machinist friend coming in a few days to get accurate measurements on the bore and crank, so I'll post back with the numbers.

John0829-Thanks for the quick reply and confirmation about the sleeves being thinner on overbore.

jaxs-Thanks, I started getting concerned about these kits when I was comparing prices from several of the online tractor parts places and saw all these overbore kits.
I had intended on getting the original 3.90 bore kit but some places have the overbore kit discounted quite a bit (and others are only selling the overbore not the 3.9 kit). This seems odd and got me wondering if there was a catch somewhere.

Heres links to a few of the site pages with overbore kits:
Restoration Tractor Parts-(only lists overbore kit)
TractorJoe (only lists overbore kit)
Abilene Machine Works
Steiner Tractor (only lists overbore kit)

Several of these places appear to be selling the Reliance brand components, others don't list a brand.

I just assumed most nowadays just install a new sleeve/piston set, but if there's a chance I can just hone and keep these sleeves and get oversize pistons, might go that route.
Please let me know if you have an opinion on brands, especially if it might be an option to just hone these sleeves and fit new pistons.

I'll post some pics of cylinders and measurements when machinist comes.

Thanks again!

 

[John0829]

The thing is a lot of folks see the overbore and think it going to make a lot more power because it is "overbore" but fact is .010 is not going to make a nickles worth of difference. Bottom line is it is a gimmick.

 

[jaxs]

Once agin I tend to agree with you John that nothing is gained with the overbore but I intend digging deeper next week. I sometimes wonder if people that sell this stuff actually understand the truth. I've made inquires to tractor parts and auto parts suppliers about exhaust valves and seats for unleaded fuel and they don't have a clue about the difference. If I were to guess,I'd say at one time someone desighned a kit taking unleaded fuel in consideration and over bored cylinders were incidental but marked the difference. The kits aquired acclaim from knowledgable mechanics and rebuilders then clever marketers captalized by omitting expensive but more important componets while retaining over bore. I might not be the smartest guy around but you must agree my imagination is secound to noone.

 

[John0829]

I see where you are going but the thing to remember is that the Ford tractors already had the hardened valve seats needed for unleaded fuel, came from the factory with em'. Nothing to change or add for unleaded fuel. Sometimes folks would remove the sleeves and put in an oversized piston to fit the block bore. That did increase the power some but still not to enough for the seat of the dyno to register much change, 3 to maybe 5 hp if lucky.

I have heard of oversized sleeves to repair a block that has been run without sleeves but that is obviously not the case with these. Be interesting to hear what if anything you find out.

 

[fordcomanche]

Thanks guys,
Yeah I can see that Overbore kit being used a marketing/sales gimmick--"...we can get you more horsepower for the same labor install as a standard kit and for less material cost than the standard kit...And this overbore kit is the only kit you need to stock...one size fits all needs" LOL

Reading back thru my service manual, looks like the original sleeves can be bored up to a max of .040 and refitted with new pistons.
I started checking on avail of .020, etc.. pistons just in case
But I'm also finding quite a bit in price differences in the individual pistons or ring sets alone depending on whether its std, .020,.030, .040, or the "4in Overbore".

The 4in overbore piston seems to be roughly same or less cost than the std but .020/.030/.040 pistons are higher in price.
Most of the places seem to be selling either Reliance or Sparex brands, havent seen much in way of other brands.

Havent been able to get at motor for measurements due to weather, but anxious to readings.

Thanks

 

[John0829]

When I rebuilt, well replaced actually, the block I found was from a 64' 4000. Same engine only it does not use sleeves, bored it .040 over to clean it up and got the pistons from Tisco. Don't remember who made them but the cost wasn't bad, mind you the work was done in 2014.

 

[fordcomanche]

Thanks John, I'll check on the Tisco parts.
I have everything disassembled and the engine block is out of the tractor. It had quite a bit of rust inside from the floodwater, mostly up around the camshaft and lifters. The rust seems like mostly loose scale and seems to be coming off with minimal pitting.
I talked to machine shop and I'm planning to get the block and head hot tanked and got prices for cleaning up the original sleeves and boring them .020 over
(Looks like just boring the original sleeves may be the best option right now if I can get a set of .020 pistons and rings with all this "supply chain" shortages. Most are just carrying those 4" overbore kits and pistons).
Heres some of pics of the block