Q on piston rings

[gwb72tii]

unbelievably, the block in our tii doesn't need to be bored (a first for me) and I can re-use the pistons, but should replace the rings

any magic to which rings to buy (Mahle pistons)??

[02fanatic]

I'm just curious, how did you have it checked?...machine shop?...do it yourself? I have an extremely early tii engine awaiting a rebuild...and I'd like to keep it stock if possible too.

Thanks,

John

[jimk]

I'm just curious, how did you have it checked?...machine shop?...do it yourself? I have an extremely early tii engine awaiting a rebuild...and I'd like to keep it stock if possible too.

Thanks,

John

Strip the rings, measure clearance with piston in hole in the correct position and below the top ring stop where the maximum wear occurs on the drivers side of the hole. If in spec, glaze break and look for low spots. If minor re-ring and go. It's not a purist's overhaul, but a lot of rebuilds needlesly bore.

[02fanatic]

I'm just curious, how did you have it checked?...machine shop?...do it yourself? I have an extremely early tii engine awaiting a rebuild...and I'd like to keep it stock if possible too.

Thanks,

John

Strip the rings, measure clearance with piston in hole in the correct position and below the top ring stop where the maximum wear occurs on the drivers side of the hole. If in spec, glaze break and look for low spots. If minor re-ring and go. It's not a purist's overhaul, but a lot of rebuilds needlesly bore.

Yeah, I've got alot to learn in this department for sure....but I've always wanted to do a total rebuild myself...well, as much as I possibly can myself anyway. I've always suspected many rebuilds were done needlessly. I'd like to not overbore, etc., unless absolutely necessary...one reason is trying to find stock bathtub tii pistons!

Thanks for the info!

[bevans6]

how did you actually measure the clearance? The only way I know involves a dial bore gauge to measure the bore for out of round and taper, and a micrometer to measure the piston skirts. If you measured with the piston in the bore as it sounds, I wonder how you did that.

Cast pistons usually run fairly tight clearances. It's often possible to install forged pistons, which use looser clearances, by just honing to clean up the bores. It's also really very possible to just re-ring and deglaze and re-use the existing pistons. You need to check to see that the skirts are not collapsing by comparing to new piston specs, and you need to check the ring lands to see that they have not opened up too far. That's what I call an engine "refresh" instead of a "rebuild".

Cast iron Moly rings are good to use for re-ringing. A ball type hone will give a good finish, but won't straighten the bores at all.

Brian

[02fanatic]

YOu answered some of my questions Brian....I have one more though, and please excuse my ignorance, but what does "deglazing" mean? cleaning the pistons up in a blast cabinet?

[jimk]

please excuse my ignorance, but what does "deglazing" mean? cleaning the pistons up in a blast cabinet?

To remove the glaze is to just remove the shine by using a glaze breaker. It doesn't remove much material, just roughens the surface so the new rings wear in to seal.

Google Lisle 23500 glaze breaker.

Measure clearance with the piston held in the hole upside down and feeler gauge on the skirt 90degrees from the pin. See your manual for inservice clearance.

[02fanatic]

Thanks for the info!

[Guest]

moly works great on a "Round" hole . On a re ring "According to a friend who is a hard parts jobber/warehouser in the mid west and hot rodder" go hastings cast iron. It will be more tolerant of a less than round hole. For a new round hole use a no gap type ring or moly on an iron detroit V8.

WARNING

have good seals on the valves your new rings will Suck Suck oil by the valve guides and seals .Learned the hard way

[trangieboy]

Buy plus .010" rings and file fit the ring ends for correct end gap.The bore WILL have slight wear and standard rings will have an oversize end gap.

Mal.

[bevans6]

YOu answered some of my questions Brian....I have one more though, and please excuse my ignorance, but what does "deglazing" mean? cleaning the pistons up in a blast cabinet?

I would be very careful of media-blasting pistons, it's all too easy to ruin the fit of the pin bores and the ring lands. If you do this, tape off all but the piston tops...I use solvent and rags to clean the pistons, or a 3M pad.

Deglazing refers to the bore surface in the block. If there is ANY ridge at the top, you really should be boring and fitting new pistons. If there is no ridge, you need to create the new cross-hatch finish in the bore surface for the new rings to seat to. That's deglazing. Honing is when you use a Sunnen type hone that removes a small amount of material and creates a truly round and taper-free bore (in the hands of someone who knows how to use it). There are manual hone heads but most shops use an automatic machine. These are NOT the $12.95 three stone things sold in cheap autoparts stores, they are good for light deglazing only...

Brian

[Guest Anonymous]

I have several sets of used pistons from which I would like to choose a good set for use in a spare engine. None of the pistons were cleaned up other than wiped down with an oily ATF-impregnated rag and placed in plastic bags for storage. A couple pistons look as though they were polished. Others have the patina and color of a well seasoned 100 year old frying pan. A few questions follow:

Is it safe to "hot tank" pistons? Or, should I stick with scotch brite and kerosene or some other solvent?

Did Mahle ever make pistons with a few (8) tiny holes (drilled?) around the outside of the piston tops through to the top ring land?

TIA

[gwb72tii]

John,

sorry to reply so long after my post, but i've been busy and just checked

my machine shop guy miked the bores in 3 places, bottom, mid and top. then he checked the diameter of each respective piston at the same locations to measure total clearance, and then to check Mahle specs to determine if the clearance is within specs, which mine are.

then he miked the piston ring groves in each piston to determine if the pistons were reusable. there is a max clearance allowed, essentially the width of each groove compared to the thickness of the piston ring. mine are ok.

now, let me mention one thing here. I've personally rebuilt 4 2002 motors, and this is the only time I won't need a rebore of the block. my machine shop guy mentioned before he measured everything that the bores looked really clean and new - the crosshatching was easily seen and was similar to motors i've put together after a rebore. my motor is already on the 2nd oversize, so the motor has been through at least one rebuild prior to my ownership, but when and how many miles ago is unknown. the darn thing was leaking so much oil, i figured i'd rebuild the motor for general purposes, and am quite surprised to get the above info from the machine shop.

also, when deglazing is mentioned, it is to the bores, not the pistons. personally, i'd never media blast a piston to clean it. if you screw up the ring lands, the piston is toast, and as you well know, these babies are NLA.

i'm with you, i'd like the car to be essentially stock, so sticking with Mahles is good, and now i won't have to spend $ on boring and custom forged pistons.