924Board.org

[Mike9311]

I am working on an engine using very lightweight long rods already in hand for a stroker setup. Wanted to wait until I was all done to post up. The set-up will be piston guided with bronze washers. I was going to go tighter than what you stated Anthony based on my research i was seeing 0.005" but I'll confirm for you. I figured I would have to machine the piston sides flat for the washers. It will also be using custom rod bushings so I can control the piston pin location. I have already confirmed the rod end clearance. The real problem is still off the shelf piston choice -CC especially for a stroker. I went this route after spending 2 months designing a custom piston only to find out how insane material cost would be. Could have bought a car

522g 153mm long rod custom bushed for 22mm wrist pin to control compression height and quench distance as well as overall piston choice. Right now that's a 313g forged piston. Posted these up on my flickr in dec



The casidium coated 22mm are shorter and lighter (I was hoping for the advertised 95g but it is what it is...). The 22mm lets me play with offset bushings in the rod and compression height.



Early version of the abandoned piston project if your curious. If you see any design with bridge support like this one, a great amount of time went into the design. Later, I quit using them to give the piston more "give" and the ability to spread the load. The bridges concentrate stress...anyway, like I said, I abandoned this and went for off the shelf pistons. 313g units that I am also working on a better way to oil cool. The real problem for the stroker is my head will be major custom to use these pistons. This will be for another thread. The point here is the rods



Fitting up the rods to check clearance with plastigauge. Edit: that's a Crower on the far right



Edit: The final version of the piston when I quit wasting time on it. I had 3d printed versions in a block etc. Lost too much time


_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

[Mike9311]

Rod bearing choices become much cooler too


_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

[anthonimartini]

thats some great work! its funny that ive become so worried about the side clearances in this project because the aircooled VW engines ive built over the years all had massively varying clearances and i never once had any issues. none were over the .100" gaps i was getting with this 924 project though. i also talked to a local machinist (brian at bearing services) about going the route you did, custom piston controlled rod setup but it quickly exceeded my meager budget. and alas i went full circle to lightening the stock rods. there are still some nice made in germany rod bearings available on ebay in undersize, so i cut my std crank to use those.
_________________
ive saved alot of 924's
current:
79 MochaSchwartz 931
83 944
87 924S
Instagram @anthoni.jpeg
formerly known as turbellion, lost password.

[TJC]

There are various reasons to control clearances and side play at the big end of the rod not the least is oil control. Excessive clearance at the big end can cause improper oiling as the side play clearance and fillet design as well as even the size of the chamfer on the crankpin oil hole all play a part in proper engine oiling to some degree. That is one of the reasons that rod side clearance at the big end is the method used to control rod movement and not at the little end. When building a high performance or race engine the builder also relies on building to a specification and not a tolerance and uses the proper measuring tools, parts, machines, knowledge and experience to do so. Tolerances are fine for manufacturers as most engines are never used to the extent that they're designed for. With the thousands and thousands of engines they produce if they have a low failure rate percentage due to an engine being on one side or the other of those tolerances and an end user is punishing the engine to it's limit and it blows up, it's not a big deal to them. When you're building a specific engine for a specific purpose and especially for a specific customer who's footing the bill the mindset is a bit different! However having said that not everyone wants to be building an engine to such exacting specifications as they may not be able to justify the extra research, time and expense for their intended purpose. And unless one intends to use their car for some serious competition or harder than normal use they probably don't need to. Hell in the old days engines ran with dippers on the rod caps, poured Babbitt and relied on splash oiling and they served their purpose! Personally, I would pay attention to the big end side clearance in any engine I build regardless of which rod I would end up using.
_________________
'95 BMW 318i/5 ..."Pearl"
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"
'04 BMW X3..."Xander"
Still on the Prowl!

www.ttrs1.com

[Mike9311]

It was interesting to go down this rabbit hole when researching every option. For me the easiest thing to do would be to just buy custom pistons though I wanted to exhaust my off the shelf options if there were any.

Nascar tech brought to where I'm at currently and there is that debate exactly regarding big end side clearance. I too felt like it was a tad crazy at first but they are doing piston guided rods in a lot now. Nascar did it to reduce friction and big end weight. There are issues however. You need to control the rod vertical position and therefor the pin washer clearance needs to be tight. A loose big end doesn't help matters. Then there are potentially oiling issues both for the washers and the pin. There are differing methods of handling that via washer design, one of which I think is strange.. oval shaped on the pin to allow pin oiling from the pin at the piston to travel along the pin. Personally I think that's a machining nightmare. Holes and feeder slots would be my choice

One of the things I was checking out of curiosity in the other photos was how the big end tilted when comparing bearing clearance and rod type.

Keep in mind I have never done this before but have been investigating for a little while now this winter and posted when I saw the discussion. Its hard to find any rods wide enough for our app and the same big end size.
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

[Juho]

im gonna order 5 sets of 924 rods with 22mm smallebd bores

[anthonimartini]

if you do that let me know i would buy a set, let me know what they charge you for that!
_________________
ive saved alot of 924's
current:
79 MochaSchwartz 931
83 944
87 924S
Instagram @anthoni.jpeg
formerly known as turbellion, lost password.

[Juho]

i going to get some rods made gonna take 30-60 days