Super Mini Mad
Posted 01 April 2019 - 06:02 AM
For the life of my I just can't find any 998 press fit pistons on sale anywhere! At least something affordable. Everyone seems to be selling circlip types.
I searched on the forums and read that its possible to fit the convert the press fit to floating gudgen pin by honing the little end and putting some button?
Could someone explain in greater detail please? Preferably with pictures if possible.
Moved Into The Garage
Posted 01 April 2019 - 06:31 AM
The Press Fit Rods were only used for 2 maybe 3 years in production. When 'compared' to floating type Rods, they are probably in the 'odd ball' class hence the lack of availability of Pistons etc for them.
As you are a little tight for funds on this Project, I'd suggest a better way forward with be to obtain a set of Floating Pin Rods, given how popular they are and that they are for the smaller engines, you'll possibly get a set for free or very cheap, I think this would serious de-complicate matters.
Regardless as to weather you keep your old rods or go down this path I would strongly suggest having the Rods reconditioned.
Super Mini Mad
Posted 01 April 2019 - 07:30 AM
Up Into Fourth
Posted 01 April 2019 - 07:39 AM
Car and Car Conversion had an feature on circlip failure and the merits of press fit pins.
About the same time, I was asked to remove the bushes from a set of rods for a guy.
As he was drove off, he told me he was just going to pick up a set of pins that he was having specially ground-------- oversize in the center !!
I have often wondered what he said when he tried to fit them.
Moved Into The Garage
Posted 01 April 2019 - 07:45 AM
Reconditioning Rods should include;-
Crack Test,
Check for Cap Fit,
Close on the Big End - this is where the cap and rod are ground back on the mating faces. It's only a few thousands.
Fit Cap with new Fasteners (the current new ones are dubious in quality and I would suggest ARP Fasteners)
Hone Big End to Round and Size,
Check Little End Bush - often they are OK, replace as required and Hone to Size
Check for Bend and Twist - correct as required
You can waste money on having them balanced as well.
<Edit: With Press Fit Rods the process is similar but a little different.
First thing is to check the Little End. If they have been heated, then they should be binned.
Next, if they haven't been heated, is to check the Little End Size and finish, checking for galling or other damage,
The rest is pretty much as above,
However, a final test is done when fitting the Pins. This is recommended by the Factory to be done COLD and the pressure needed to Press the Pins checked all the way 'home'. It Must Be above a certain value and if not, then the Rod shouldn't be used as the Pin will likley walk out in use.
Personally, I'm not crazy about Press Fit Pins and will never use them for any performance application. >
Edited by Moke Spider, 01 April 2019 - 07:53 AM.
Super Mini Mad
Posted 01 April 2019 - 08:39 AM
Super Mini Mad
Posted 01 April 2019 - 08:40 AM
Moved Into The Garage
Posted 01 April 2019 - 08:50 AM
Still i thought the reason for changing to press fit is because that is sturdier than the floating pin?
Press Fits are cheaper to manufacture.
Super Mini Mad
Posted 01 April 2019 - 09:56 AM
So Moke, what do I do with these bushes? http://www.somerford...roducts_id=6625
Do they just as act as a spacer to allow fitting floating pin pistons to press fit conrods? or would the conrods still need to be machined somehow?
Camshaft & Stage Two Head
Posted 01 April 2019 - 02:23 PM
Press fit gudgeon pins do mean you avoid problems with circlip retention groove wear in the pistons.
Up Into Fourth
Posted 01 April 2019 - 06:43 PM
A downside with press fit pins is that if they are not a suitably tight fit in the rod then the gudgeon pin can walk and score the bore.
Another issue with press fit pins is taking apart/reassembling the pistons requires a special tool. Circlip pliers are much easier to find.
Swings and roundabouts.
Moved Into The Garage
Posted 01 April 2019 - 07:36 PM
So Moke, what do I do with these bushes? http://www.somerford...roducts_id=6625
Do they just as act as a spacer to allow fitting floating pin pistons to press fit conrods? or would the conrods still need to be machined somehow?
They are what is fitted in to the Little End of the Floating Pin type Rods. Often you'll find what's in them is OK, and sometimes they need replacing. When I used to recondition these Engines, I would as a matter of routine replace the Bush as that's what the customer was paying for, however, in probably 70%+ of circumstances, they were on size and not showing wear. So, you'll likely find what's in the Rods you are buying, the Bushes will be OK. They do need to be Honed to size after fitting, it's a Machine Shop operation.
Press fit gudgeon pins do mean you avoid problems with circlip retention groove wear in the pistons.
Yes but as Carbon has said;-
A downside with press fit pins is that if they are not a suitably tight fit in the rod then the gudgeon pin can walk and score the bore.
Another issue with press fit pins is taking apart/reassembling the pistons requires a special tool. Circlip pliers are much easier to find.
Swings and roundabouts.
I've seen more than my fair share of Press Fits go for a walk and often it's not picked up until the engine starts burning oil, by which time, usually they are up for a sleeve.
Withe the Circlips, they can also fling out and that is always a risk, however, it is important that they are fitted correctly in the first place The Groove in the Piston must be checked for size and that it's clean. The Circlips themselves are made from Pressings, so they have a 'rounded edge' side and a 'Sharpe edged' side. It is absolutely critical that they be fitted 'Sharpe Side' out so the 'bite' in to the Piston. Fitting them the other way they will almost certainly come out.
Lastly, 2 further things I always did with them to assist in their retention was to fit the 'Ears Up' or 'Ears Down' so that the reciprocating motion and Harmonics are less likely to close them when fitted and lastly a drop a Loctite as insurance. Touch wood, I never had a clip come out.
IMO, the best means of Pin retention is to use Floating Pins and Teflon or Aluminum Buttons. There is simply no way the Pin will give trouble. It all the quick engine I built, That was what I have done.
Moved Into The Garage
Posted 04 April 2019 - 07:33 PM
On the question of the Pistons and Pins being different between Floating and Press fits, they are the same.
You can indeed fit 'Floaters' in this instance, to Press Fit Rods, just don' try and also fit the circlips !
Camshaft & Stage Two Head
Posted 04 April 2019 - 08:21 PM
Fair enough. What on earth is Des Hammill on about in his book then?!
Moved Into The Garage
Posted 04 April 2019 - 09:41 PM
Fair enough. What on earth is Des Hammill on about in his book then?!
I don't have Des's small bore book, so I can't really comment on that.
I do prefer to rely on Factory Data for hard numbers like these.
Des's books are good IMO for the guy at home, they do go that step in between the Haynes kinda material and professional books.
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