pepcak Posted December 5, 2015 Share Posted December 5, 2015 Restoring 28 Master Six I have find out that cylinders are quite out of round (shop manual specifies 0.002, mines are at about 0.01. Thinking about bore it straight and use oversized pistons. I want to go with cast iron pistons but have difficulty to find suitable replacement. Those from Chevrolet Master appear to fit but the piston pin has no offset while Buick ones have 3/32". Two questions 1) Is it a real issue to use pistons with no offset while originally an offset is specified? 2) Any chance to find cast iron pistons with exact 1928 Buick Master spec? (3 1/2" / 0.01 to 0.03 O/S; comp. height 2 3/16"; pin 7/8"; pin offset 3/32"). Bare castings OK, I can have them machined. Any help appreciated. Josef Link to comment Share on other sites More sharing options...
Mark Shaw Posted December 5, 2015 Share Posted December 5, 2015 Josef, Please explain why you want to use new cast iron pistons. Converting to aluminum pistons significantly increases the engine's efficiency by reducing the piston weight that the engine must move on every rotation cycle; using aluminum pistons and modern rings can increase usable engine power by about 10%. Link to comment Share on other sites More sharing options...
pepcak Posted December 5, 2015 Author Share Posted December 5, 2015 I just want to keep things stock, do not want to elaborate much with re-balancing the whole thing and with piston / cylinder clearances. Link to comment Share on other sites More sharing options...
Guest Posted December 5, 2015 Share Posted December 5, 2015 JosefI have a poor sister to your Buick (Pontiac). When I rebuilt my engine I went to aluminum pistons with 3 rings above the pin rather than three above and one below. There was no problem with having to balance anything at all. As Mark Shaw said the increase in power is about 10% but with the low horsepower to begin with the ease and comfort in driving is unbelievable.Reid Pearce Link to comment Share on other sites More sharing options...
Pete Phillips Posted December 6, 2015 Share Posted December 6, 2015 (edited) I have dozens and dozens of new old stock cast-iron Buick pistons from the 1920s, from when a long-time Buick dealer in Sherman, Texas went out of business in the early 1970s. They all have a very light coating of surface rust which will buff off with a quick flick of sand paper. If that doesn't put you off, I will start measuring. They are not organized as to size. It will take a lot of time to do this, so I'm not going to start unless you are seriously interested. Normally, I get about halfway through measuring and taking photos, and the person who sent in inquiry either changes their mind or finds something "better". Sorry to be so negative, but I've been through this too many times with people on this forum. Pete Phillips, BCA #7338 Leonard, Texas pphillips922@earthlink.net P.S.: These have the 1920s Buick logo stamped on the inside of the piston. Edited December 12, 2015 by Pete Phillips (see edit history) Link to comment Share on other sites More sharing options...
1967 - 1997 Riviera Posted December 11, 2015 Share Posted December 11, 2015 Whichever route you take, do not install pistons without the originally designed offset. Link to comment Share on other sites More sharing options...
bradsan Posted December 12, 2015 Share Posted December 12, 2015 I'm curious as to the theory behind not installing the pistons without the offset when going to aluminum pistons?Which begs the question why the offset was there to begin with?There is a lot of discussion on line about modern performance issues but that probably doesn't apply to these engines. There are also comments on offset reducing piston slap; that might have been more of an issue with cast iron and would make some sense if Buick was trying to make a quieter engine. Later engines didn't have itI had a set made up by Ross for my 25 Std with a shorter skirt and no offset based on their recommendation. Haven't installed them yet so I can still do something instead of lying awake worrying about making the right calll!!! Wouldn't be the first mistake I've made and likely not the last! Brad Link to comment Share on other sites More sharing options...
Leif Holmberg Posted December 12, 2015 Share Posted December 12, 2015 What meens with "offset"on a piston.Never heard of it before.Leif in Sweden. Link to comment Share on other sites More sharing options...
Pete Phillips Posted December 12, 2015 Share Posted December 12, 2015 Off-set = Piston pin not mounted in the very center of the piston's side, but more towards one side or the other. Link to comment Share on other sites More sharing options...
Leif Holmberg Posted December 12, 2015 Share Posted December 12, 2015 Thanks Pete.Leif in Sweden. Link to comment Share on other sites More sharing options...
dibarlaw Posted December 12, 2015 Share Posted December 12, 2015 Josef Thank you for bringing this up. My 1925-25, 191 cu.in 6cyl is pretty tired and noisy. I will soon be looking at a rebuild and I will go with Mark Shaw's recommendation and go with aluminum pistons. I see Brad has moved in that direction an his 1925 Standard. I will ask him for the contact info for "Ross". Link to comment Share on other sites More sharing options...
Leif Holmberg Posted December 12, 2015 Share Posted December 12, 2015 To buy old cast iron pistons are a challange just becuse there hard to find piston rings that will fit that wide .When I was looking for original 3" rings for my last restored 1925 Std.I get rings from 4 different kits(I bought them from a very big piston ring shop in US)When buying new aluminum pistons and the rings,the rings are half as wide as the old ones,and that`s a + as well as the not so heavy pistons.Leif in Sweden. Link to comment Share on other sites More sharing options...
bradsan Posted December 12, 2015 Share Posted December 12, 2015 Larry Ross Racing Pistonshttp://www.rosspistons.com/My dad's buddy used them for his 29 LaSalle.I was going to go with a major antique parts supplier but wasn't happy with the quality of some of the parts I previously received from them ( I think they were having some 'issues' at the time, maybe things have improved since then?)Ross was helpful, they came with wrist pins and rings (solves the problem of finding rings for stock cast Iron!) If I'm not mistaken, the originals had four rings, Ross reduced it to three because the modern oil rings are vastly superior to the 1925 tech used. Price was a little cheaper than the other firm. That said , they are still sitting in the box 8 years later waiting for me to be the guinea pig!!!The offset is more than just a few thousands, it is actually quite noticeable.I worried about the offset when I ordered them. Ross said they could do it either way but their recommendation was to centre the pin bore and get some sleep.Still, I'm always curious about other opinions. Brad Link to comment Share on other sites More sharing options...
pepcak Posted December 13, 2015 Author Share Posted December 13, 2015 Thanks for all the responses. I understand all the reasons about significantly lighter Al pistons (I have some Al pistons of 3.5" size that are at 547 grams vs 911 grams of the original piece). I still think that using iron ones will keep the car closer to original spec with "stock" (?poor?) behavior & performace. From what I found on internet the pin offset helps to reduce load on cylinder wall during the expansion period of the cycle and reduces noise / slap. Possibly not a big deal on 2k rpm engines and possibly even less with Alu pistons. Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted December 13, 2015 Share Posted December 13, 2015 For what it is worth, the 263 piston has an off set of 1/16th inch. Ben Link to comment Share on other sites More sharing options...
Terry Wiegand Posted December 13, 2015 Share Posted December 13, 2015 And what happens if a person doesn't get this 'offset' on the right side of the cylinder? I'm with Leif, never heard of the like before. This sounds like a setup for uneven wear in the cylinder. I want to make sure that I am understanding what I am reading here. Ben, are you telling us that Buick deliberately built their engines doing this? I am considering very seriously having the engine in my 1916 D-45 completely rebuilt. You can bet your bippy that I will go back with aluminum pistons, modern rings, and have the rotating assembly balanced. That Light Six Buick engine was a powerhouse to begin with and doing this will only increase power and smoothness. I am a huge fan of originality in restoration, but, doing what I want to do will not show and the person looking at the engine will never know that anything out of the ordinary was done internally unless I tell them. And what happens if when the engine is opened up and some cylinders are found to be tapered or out-of-round, or both. It will have to be bored to straighten things up and then God forbid, it isn't original anymore. The point I am making here is this - if certain things must be done, what is the harm in 'modernizing' the internals a bit and making the engine more dependable and trouble free. I really want to hear what the supposed purpose of a piston wrist pin offset is all about. This just doesn't make a lick of sense to me. What say you all out there? Terry WiegandSouth Hutchinson, Kansas Link to comment Share on other sites More sharing options...
Pete Phillips Posted December 13, 2015 Share Posted December 13, 2015 This summarizes the reason for offset piston pins: http://www.motorcycleproject.com/text/cows-offset.html To summarize it in a couple of sentences, it reduces the crankshaft turning stress on the connecting rods and on the pistons. It also allows for the use of lighter weight pistons and higher r.p.m.s. The connecting rod spends most of its time at an angle, compared to the up & down piston movement. It helps to compensate for that angular force, as I understand it. But as usual, I'm sure there will be those on this forum who will disagree. Pete Phillips, BCA #7338 2 Link to comment Share on other sites More sharing options...
Terry Wiegand Posted December 13, 2015 Share Posted December 13, 2015 Pete, thanks for putting that article on here and educating us about this engineering point. I certainly was not aware of this purpose. In the case of my '16, we are dealing with a slow speed and low compression engine. As time went by the compression ratios increased, engine speeds increased and inti-knock fuel came into being. It was stressed in several places in the article that by doing this it would allow for higher engine speeds. When I take my engine to the rebuilder I will talk to them about this. Maybe this is something that will not be necessary in this engine. It sure is and has been obvious to me that a person can learn a lot in playing around with these old cars. Something else that really amazes me is the degree of technical innovation that Buick employed for only being in the business of building automobiles for a little over 10 years. Terry WiegandSouth Hutchinson, Kansas Link to comment Share on other sites More sharing options...
Larry Schramm Posted December 13, 2015 Share Posted December 13, 2015 Something else that really amazes me is the degree of technical innovation that Buick employed for only being in the business of building automobiles for a little over 10 years. Terry WiegandSouth Hutchinson, Kansas I agree. My 1915 Truck has roller lifters. Link to comment Share on other sites More sharing options...
ROD W Posted December 14, 2015 Share Posted December 14, 2015 Thats what,s great about this Forum, you learn new things every day. I rebuilt my 25 standard engine 30 years ago using Aluminium pistons from egge. didn,t even know about offset, so if there was offset in the wrist pin, they probably went in the wrong way. The engine in my 1920 K-44 is very tired and smoky so like Terry,s 1916 it is time for a rebuild. I was thinking of just putting new oil rings in, but I think I will let the piggy bank build up a bit and do the job properly with new Aluminium pistons. Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted December 14, 2015 Share Posted December 14, 2015 Terry, the 263, that debuted in the 1950 Super was built this way. The shop manual does not say why. And they, of course, are not flat topped pistons, with a dome to one side. Difficult to install wrong. Ben Link to comment Share on other sites More sharing options...
LAS VEGAS DAVE Posted December 14, 2015 Share Posted December 14, 2015 Offset piston pins have been around for at least since the fifties in all overhead valve engines. Link to comment Share on other sites More sharing options...
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