I'm planning my engine build, and I'm looking at which rods to use. I have a 78mm crank, and from what I've been able to determine, if I use 3.325" rods, I'll likely need to flycut the case (my estimate is .020") or live with a larger than optimal deck height. I can get suitable 5.5" rods, but then I figure I need 4mm (0.16") cylinder shims. Does anyone make such a thing? The largest that I can find are .090". Also, does anyone make a shim for the pushrod tubes? I figure that they will need to be shimmed out 3-4mm to seal properly. Looks to me like there is room for that in the case. Finally, this will make the engine a total of 8mm wider than stock... I can't see this being a big deal, though... right?

I'm not gonna comment on the cylinder/rod/whatever part of the question, other than you have to calculate the shims, you can't just throw some at it. The pushrod tubes are floating. I dunno how you'd shim them unless you made some "stops" for the inner end to keep the outer ends within the range where they'll seal properly. I doubt it's necessary, though. The Cap'n

Is the crank 78mm or 78.4mm?
What CR are you designing this motor to achieve?
What pistons and pin height have you chosen (that will determine rod length)

Aside from squaring up the case you should not need to remove material from the case.
You want rods that may be a bit long with no shims and then you use the shims to lower the CR to an acceptable number, your target CR.
Jake can have any shim you need custom made when you figure out what that number is...
FAT does stock some shims, not sure what they have in stock.

Who did you get the crank from?
Have you called Jake/FAT to ask then what rod they use for your crank?

Rich

I measured it at 78mm

Undecided yet, but somewhere in the 9.0-9.3 range

Pin height is 1.110"... ideal rod length with no shims would be 3.345", which is not an option.

From what I understand, CR is set with chamber volume, not with deck height.

5.325" rods look like they will be .020" too short, and something will have to be milled to get me the proper deck height. 5.5" rods will require abnormally big cylinder shims, in the order of .160". 5.5" rods give a better rod ratio, but the type IV already has a better rod ratio than most engines.

A guy named Bill It is counterweighted and has type IV rod journals. The rod journals limit my choice in rods.

No, since I did not buy the crank from them, I did not feel it was appropriate to ask them questions about it. When I do buy parts (rods, pistons, cylinders), then I'd be comfortable asking questions...

Understood. I have measured what I can at this point, and mocked up the dimensions in CAD. What I have is an approximation, and will be measured exactly upon assembly. I'm just trying to get an idea where I stand, and what parts I'm looking at. 5.325" rods are close, but my estimate is that they will result in .020" excess deck height. Not the end of the world. 5.5" rods would give a better rod ratio, but would require large shims that I have not been able to find anywhere. Yes, I know that rod ratio is a minor consideration in the scheme of things...

I also have a set of clearanced stock 2.0 rods that I could use with stock stroke pistons big ass cylinder shims. I do not want to go that route. I can't see anything good coming from that.

Yes, the "stops" that you describe is what I'm talking about. I'm not sure that I can move the heads out 4mm and still have the pushrod tubes seal... I really haven't looked that closely at that measurement yet on the head end of the tube. On the case end, it looks like, if I need to, I can put in a 3mm shim and still have the pushrod tube seal within the machined area of the case bore.

Just trying to get my waterfowl aligned Doing my best not to have to take any backward steps in this build.

I agree with Crusty. Trying to calculate may get you close but, you really need to mock it up. The real issue will be clearing the cam. You need a reduced base circle cam most likely. There may also be clearancing on the case that needs to be done.

You mentioned clearanced rods so that's going to help.

You really need to get parts in hand and mock it up.

Dave

Way back when before we had so many cool parts available, I built an engine using 0.25" (1/4 inch) cylinder shims ( I think I got them from Rimco).

I got two sets of P/R tubes and cut and welded them so they were 0.25" longer. No issues putting the engine in a 914.

Got one.

I'm okay with that.

I guess my point wasn't clear. I'm not looking to buy the parts based solely on my calculations. I'm trying to find out if the parts are even available. I don't want to bark up the wrong tree. I don't want to buy the wrong rods only to find out that they cannot be made to work. The largest cylinder shims that I've been able to find are .090". I've found people saying that anything larger is called a "spacer", which leads me to believe that they are indeed available. But, I have not found a source.

Riddle machine Company = Rimco

But you have to have all your parts first, measure and then they make the shims to your spec.

Todd,
Check this place for custom shims/spacers http://www.cevw.com/products1.htm
Kev

Thanks, James... that's helpful. I don't really want to weld pushrod tubes. I've found "stroker pushrod tubes" that are .400" longer than stock, and very expensive.

Shimming the pushrod tubes out looks like a possible solution to me... I'm just wondering if anyone has done it... or am I nuts? I don't think that I can just move the heads out 4mm and still have a good seal. My initial assessment says perhaps that is why .090" cylinder shims are the largest that I can find... that is as far as you can go without addressing the pushrod tubes.

I'm running .130 shims on a 78X103mm nickies engine that I built....no issues.

Eureka!

I searched the Type IV Store for "shims" and got what I was looking for (in the past, my searches were too specific and didn't find what I wanted).

Precision Ground Base Shims 6508 - .060"-.500" in .010" increments

Push Rod Tube Shim #73 - for stroked engines (no measurement given, though)


I'm not nuts, at least as far as this goes

Type IV store IS Jake's place. not like we didn't "told you so"

What is your reasoning or rationale for the rod length you are choosing?

Yeah, I know. I looked there before, and I didn't find what I was looking for. My searches were too specific. And, Jake's got enough going on that I don't need to be bugging him with questions until I have $ in my hand. If he wants to chime in here, that's great.

My choice for rods, as far as I have been able to find, are:
5.160"
5.325"
5.500"
5.700"

Stock 5.160" rod length won't work with stroker pistons. Will work with stock stroke pistons and large cylinder shims. Not worth it.

5.325" rods will work with stroker pistons with minimal cylinder shims, or, by my calculations, will result in slightly too much deck height with no cylinder shims. As far as I can see, reducing deck height requires machining. Possible.

5.500" rods will work with stroker pistons and large cylinder shims (approx 4mm or .160") and pushrod tube shims. Looks like my best choice.

5.700" rods will work with stroker pistons and huge cylinder shims (approx 9mm or .350") and will require longer pushrod tubes. Things are getting out of hand at this point.

Another consideration, although not as significant, is rod ratio. Stock is 1.85, which is pretty good. With a 78mm crank, the stock rods give a 1.68 ratio, which is still not bad compared to most engines. 5.325" rods give 1.74, 5.500" rods give 1.79 and 5.700" rods bring you back to the stock rod ratio at 1.86.

At this point, to me it looks like 5.5" rods are my choice because deck height can be set without machine work, and they give a more favorable rod ratio (more torque and lower piston velocity).

first, the CR is calculated by the chamber volume...that includes the CC of the head and the CC of the cylinder with the piston at TDC...it would also include any dish in valve relief in the piston..

So, this is just me, I get the head CC's to match first.
Then choose the cylinder base shims to increase (thicker shim) or decrease (thinner shim) the total volume of the combustion chamber.

Now, we may be talking the same thing, I am not sure so that is why I said it.

Rich

Yup. My heads are pretty close to where I need them to get in the 9.0-9.3 range with a 1mm deck height. Might have to add a cc or two to the chamber.

I understand that you can change the CR by changing the deck height, but the air/fuel mixture in the squish area won't burn well. I'd like to keep my deck height at ~1mm (.040"), and adjust the CR by telling Len what size chambers I want

what a good learning process building a type IV is

what heads are you using?

mike

I have two sets of 2.0 heads. I plan on sending one set to Len Hoffman when the time comes. I've discussed it with Len, and I'm pretty happy with what we've come up with.

I'm learning a lot through research, and having fun while doing so. Learning is fun. I'm feeling more and more confident that I am on the right track, and by the time I actually start my build (hopefully in the spring) I think I will have all the knowledge that I need to be successful. My goal is a 78x96 2258cc engine that makes 150 HP with a flat torque curve, peaking at 5500 RPM but with the capacity to rev to 6500 so that I don't need to short shift. Topping it off, my target is to do it for under $4k carbs to muffler.

Do yourself a favor and just buy all the parts from Jake at the Type 4 store. You will be much better off now and in the long run. Get the 78.4mm crank with Type 1 journals along with the proper 5.4" H-beam rods to make the 2270cc engine. It's been tried and tested. Jake has all the other parts you have questions about...the pushrod spacers, the shims, ect. The R&D has already been done, all you have to do is buy the right parts and take your time assembling the engine.
Good luck with your engine!

Your block/crank/rods is your foundation.