Pony Motor Piston Replacement

Sounds to me like your best bet is bore the cylinders to the .060" over, that,s if you can get the rings for it.I,m not sure whether the pistons are cast for oversize in the structure or not so don,t know if the walls of the piston would be too thin if they were cut back to std. Maybe if you have more questions then go to an automotive machine shop & talk to the foreman for what,s best.At the Cat shop I have rebuilt dozens of starting engines & if the cyl. walls were worn then they were bored to clean them up & install the pistons to the fit & rings. Also many of them we put dry sleeves in the block & went back to std. size if the bores were excessively worn or scored.

I,m only saying what can be done but if I were you I,d take the block to an automotive engine rebuilding shop & have them check out the bores & see what is the way to go either bore oversize or sleeve the block.I don,t know if NAPA has pistons available or check with another Cat dealer for different size pistons if you overbore or back to std.with sleeves being installed.Guys on here post many places that sell Cat parts so when you find out what you need then check with these outfits to see if they can help. Even the Auto. machine shop might be able to help you with pistons. What is this starting engine out of?

Cat had thicker rings for the diesel engines to install if the lands got worn as I have cut lots of the diesel pistons & installed the wider rings.I don,t know if the wider ones are available for the starting engines or not but you could ask when you talk to your machine shop what can be done.When I was working yet there was no problem you just chucked the old ones & put new pistons in but today things aren,t so available so you have to go the route to get things done as parts availability is the thing.

Hi Vinny and team,
Serv. Mag. Jan. 18 1949 page 4 tells us that that a chart is included with dimensions for reboring starting engines and required piston dimensions to suit.
It goes on to say that:- "SOME pistons used as original equipment had tapered skirts, but the most practical way to finish pistons in the average Dealer's shop is to finish the skirt straight. Taper turning or grinding requires additional expensive shop equipment, and our experience has been that starting engine pistons with "straight" skirts will give satisfactory results".

I believe that the same piston body part is used for all pistons for a given engine and they are machined for the O/S required or even back to standard, laterly I believe only semi-finished pistons are available, I think there is a S/M covering this also, I do stand to be corrected on these last points.
If you let me know which starting engine you are working on I can pass on the dimensions from the chart, maybe if Ozdozer has it he may be able to post it? PLEASE.
SJ my arms still ache from turning those Manulathes to widen the ring grouves for D4/6/7&8 pistons as an Apprentice. See S/M May 31 1950!.
Regards
Eddie B.

Eddie - If I'd known you had such fond memories of those old Manulathes .. I'd have pointed you in the direction of this one, that was available just last week .. 😄

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&ih=009&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=190083195411

Here's the starting engine piston-cylinder reboring specs from Jan 18 1949, that you speak of ..

http://img227.imageshack.us/img227/2229/startingenginepistoncylcm8.jpg

I've left if full size, and in landscape format, so that the figures aren't squashed-up, and so it prints out better ..

[quote="OzDozer"]Eddie - If I'd known you had such fond memories of those old Manulathes .. I'd have pointed you in the direction of this one, that was available just last week .. 😄

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&ih=009&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=190083195411

Here's the starting engine piston-cylinder reboring specs from Jan 18 1949, that you speak of ..

http://img227.imageshack.us/img227/2229/startingenginepistoncylcm8.jpg

I've left if full size, and in landscape format, so that the figures aren't squashed-up, and so it prints out better ..[/quote]
OzDozer, does the chart apply to the pony engine on the D4-7 U also?

Hi OU@AL,
the Horizontal 2 3/4" bore line is your S/Eng.
This line covers starting engines for:- D3400, D4400, D311, & D315.
Eddie B.

Ozdozer
thanks for posting the above, I did eventually find my copy but I dont yet have the puter savvy to put the scaned in data into a post YET!.
Some years back I scavanged several profesionally bound books of S/M's, P/B's, P/L's & SNL's from the bins at the dealer. Some of these dont lend themselves to opening out to scan properly. Just now trying to get going again after dealing with DVA for 3 years.
I get the LOOK when I bring even these books inside, I thought they looked OK being bound in leatheret and gold embossed down the spine.
Regards
Eddie B.