Tell me what you know about these. Factual information only please...
Rod & Piston Question
- Thread starter Jon
- Start date
Dave Hensley
Well-Known Member
5250 rods have been around a long time. They were used in early 150's and were bottom guided. Later Merc made used them top guided using thinner small end and different thrust washers. 2002-2003 and up 280's and 300 Drags had a Chatfield rod which was the 5250 cnc machined using the Chatfield program. Piston looks a little like a Mahle. Not sure. It isn't top pinned. If it is a Mahle built for Merc it is 1992-1995 vintage.
I should have shown a better picture of those rods. Turns out they are Chatfield top guided rods. They're a little more rare than the stock stuff I am used to seeing.
Dave Hensley
Well-Known Member
Now that you say that I looked closer at what little bit of beam I can see and the parting line has been smoothed. Is that a top pin in the piston at the 7 o'clock position?
Dave, it is. So... do I run these pistons or go with a vertex or the like?
http://www.screamandfly.com/showthread.php?298857-Chatfield-Rods-from-a-2014-Drag-NEW!-pulled-them-before-running
pic of Chatfield rods
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bassracr
Active Member
From what I see visually, I would run those . I would take some micrometers and measure them all out . Maybe even send them out and have the ports modified on them while I had it apart with the money I wouldn't be spending on new Pistons haha
Scott in MN
Active Member
No, I have early 90's 245 big rods that are top guided. The only big rods with black paint on them I have are bottom guided but can be converted to top guided.
My Chatfield rods do not have any black paint on them and the beam center is machined.
Interesting. These appear to be factory machined on the bottom as the crack mark is still perfect, and the quality doesn't match the lightening work done to them. The couple of folks I had check them out locally offered to buy them too... which means I need to run them 
To answer though, not all are top guided.
To answer though, not all are top guided.
Dave Hensley
Well-Known Member
5250 is an old forging. Top and bottom guided. Chatfields I don't think had the numbers on the beams as Dickie mentions. Here is my experience with pistons. You want to run a forged piston in a nik bore. Measure the pistons 90 degrees from the pins and I will bet a dollar to a hole in a doughnut that they are .008"-.009" under 3.500". New they are at about .005" piston to wall. Every Merc piston I have seen "shrinks" after it's first few heat cycles. If the pistons have been in the hands of some metal removing "horsepower doctor" the loss of cam will be exaggerated. One weekend of racing will do it. Now, that much extra clearance in an aluminum bore that is expanding at about the same rate as the piston is going to decrease the sealing and increase piston rock hurting horsepower. That is the bad news. The other bad news is that if you want a few great hours out of a $2400 set of new Merc pistons I think they still sell them!!! Wizzards are about half that AND you can get Wizzards that the $650 per set Merc rings fit now. If I have a good set of Merc top pinned and have a block re-plated I have it finish honed at 3.4985-3.499"and use the old pistons. If the block doesn't need re-plating and the pistons are good other than the loss off the cam in the skirt.....I put rings on them and run them. Big Jon the best investment you could make in the piston/rod combo at this point would be to get a set of lite wrist pins...S3000's are nice.
Thanks for the advice Dave. Let's not bet though, and assume they are .008" under... after I just put my calipers on them
A set of Wizards are $1595ish I think I saw somewhere (are the merc rings Tn?), but can not find the part numbers on Pro Marine. Anyway, they're pretty steep for now. I want to run this thing one season I think, and see how it goes. I'll tear it back down later this year and decide if I want to invest some money into it for some more fun upgrades. The block is clean, and yes, the pistons have shrunk as you said.
What about a Vertex/Pro Marine piston with rings? They're supposed to be ok, chrome ringed, but cast.
I'm looking for the S3000 wrist pins now.
A set of Wizards are $1595ish I think I saw somewhere (are the merc rings Tn?), but can not find the part numbers on Pro Marine. Anyway, they're pretty steep for now. I want to run this thing one season I think, and see how it goes. I'll tear it back down later this year and decide if I want to invest some money into it for some more fun upgrades. The block is clean, and yes, the pistons have shrunk as you said.
What about a Vertex/Pro Marine piston with rings? They're supposed to be ok, chrome ringed, but cast.
I'm looking for the S3000 wrist pins now.
It definitely is more limited to run the hipo motors. If I were running a daily driver, I would go the 225 route for sure.
Dave Hensley
Well-Known Member
The Mercury and Wizzard pistons are both exceptionally good pistons. The nikasil bore is a difficult match up for ring material. Think about it this way. In a cast iron cylinder you have a a harder material for the ring than you do the cylinder wall. Even though it is a fraction of the total swept area of the cylinder over time it wears the cylinder out. In a nik bore the cylinder is harder than the ring. The ring at peak efficiency is touching the cylinder with a razors edge. Now double the rpm the piston in a cast sleeve usually sees for what the nik piston speed is and you have a built in accelerated wear item. Racers change rings and pistons the way casual boaters change underwear. If you expect a nik motor to get the same service as a 225 ProMax then you are plowing with thoroughbreds.
And that's why I'm going back with the stock titanium rings on the pistons above. They're $350 a set now, so I'll just plan on them being a regular maintenance item like rear tires on my mustang, but rings are cheaper than tires (I got 10k miles out of this set). When I started calling some of the really high end racers, I started getting the same answers. Run the titanium rings. I did not get the same feedback from the general public on the internet, it was 50/50 on cast vs forged pistons, but there was nothing but anecdotal evidence to back it up. Ignore what I wrote earlier - I woke up at 4am.
Engine is going back together this season as-is, new gaskets & seals everywhere, new rings, new rod bearings, etc. I've mic'd EVERYTHING and recorded it. I'll tear it down, if it makes it
, at the end of the season or sooner, and check it. I'll follow up and let you know what it looks like, with pictures.I got the best feedback from the folks on this site, both on the forum and via phone calls. Thanks everyone.
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Dave Hensley
Well-Known Member
FORGED PISTONS!!!!! Big Jon just make sure you ordered the ring for a top pinned Merc piston. I think the part number is 840663A12. I can't find them anywhere close to $350 for 12 rings. About $80 a pair shipped.
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patches
Well-Known Member
Forged pistons in a nic motor. Mercury pistons seem to hold up better than Wizards but either way use the Mercury rings. Those look like older 5250's that have been top guided. Definitely not Chatfields which isn't a bad thing. There are some very fast boats that run stock weight 5250's
These are side pinned Pistons. You are correct on the top pinned pricing.
39-848200A12 for side pinned per the fiche.
39-848200A12 for side pinned per the fiche.
If anyone wants the pistons, let me know. I'll try to sell them here first. I will clean them up tomorrow and get pics.