deadsmiley Posted September 15, 2011 Share Posted September 15, 2011 Interesting thread. I would like to note that polishing a connecting rod does not make it stronger, it makes it less prone to breaking due to removing any potential stress risers. Splitting hairs, I know. Link to comment Share on other sites More sharing options...
flyguyeddy Posted September 19, 2011 Share Posted September 19, 2011 i dont really think that the very minimal amount of machining that is required to get these to go in would really be a concern, in my opinion. the piston has 6mm from the top to the first ring groove, and i would guess that the interior of the piston would be similar. HOWEVER, only a small portion of the edge would need to be removed, sort of a bevel to match the head. might get a slight compression bump from this too. im gonna look into it a little further. next question, how do we deal with the head gasket? is there a big bore one we can buy? Link to comment Share on other sites More sharing options...
Veefer800Canuck Posted September 19, 2011 Share Posted September 19, 2011 I have heard of folks carefully trimming a stock head gasket, but I don't know how far one can go with that. Link to comment Share on other sites More sharing options...
Member Contributer JZH Posted September 19, 2011 Member Contributer Share Posted September 19, 2011 The big bore head gaskets used by TTS and Dynamo Humm are (were) modified OEM. Brian Law once told ne how he did it (using an air grinder, I believe), but I ended up having TTS install the kit and mod the gaskets for me. Ciao, Link to comment Share on other sites More sharing options...
Member Contributer RoadToed Posted September 21, 2011 Member Contributer Share Posted September 21, 2011 So has anyone got any further along with this? I gonna kick in a few things. If you want to know how much you have to play with getting the pistons decked; take one and cut it in half with a band saw will tell you much about how much material is actually there. Did it with a junk head from a Toyota pickup, I was porting the replacement. Did a lot of good cause I ripped the frame in half not two weeks after rebuilding it. Link to comment Share on other sites More sharing options...
flyguyeddy Posted September 27, 2011 Share Posted September 27, 2011 i dont have a spare piston to cut in half or else i would. im going to soda blast them all and try to machine the tops off. Link to comment Share on other sites More sharing options...
flyguyeddy Posted October 15, 2011 Share Posted October 15, 2011 i talked to a local speed shop, and we did some rough calculation based upon my guessing of the piston popup of the vfr. if i trim the piston tops to match the vfr deck height JUST enough to clear the squish area on the vfr head then i will be sitting about the same compression as before with stock bore/pistons. im also thinking of running two 900rr ignition units on this engine. one fro the front bank one for the back. ive heard they have a little more timing advance to them and i want to see how much it would affect things. i will be machining the pistons today, ill post pictures of my progress later today. also, where would someone send the upper half of the block to get it bored? i was thinking APE. Link to comment Share on other sites More sharing options...
Member Contributer kgsmotorcycles Posted October 15, 2011 Member Contributer Share Posted October 15, 2011 Link to comment Share on other sites More sharing options...
flyguyeddy Posted October 17, 2011 Share Posted October 17, 2011 i just called millenium tech and they quoted me 250 to bore and hone to my pistons for this build. not bad! Link to comment Share on other sites More sharing options...
flyguyeddy Posted October 17, 2011 Share Posted October 17, 2011 also, i got in touch with a custom gasket manufacturer for the headgaskets for this and he quoted me 100 each for big bore headgaskets. Link to comment Share on other sites More sharing options...
woody77 Posted October 18, 2011 Share Posted October 18, 2011 I ended up over here from VFR World. Considering bike projects and this was pointed out to me. Sounds like a GREAT thread (so far). flyguyeddy measured his 929 pistons, and came up with ~24mm from "top" of piston to center of wrist-pin. The TTS pistons listed a comp height of .900 and a dome of .155. Assuming that together those are the total height of the piston from the wrist-pin center, in inches, 1.055" gives you 26.7mm... Which seems awfully tall vs. flyguyeddy's numbers. Futher, the .900" comp height (anyone know exactly what dimension this is?) is 22.8mm, which matches the numbers from JZH.. So, are we (ok, you guys, until now), all taking the same "top" on the pistons?? From Wiseco's site: "Compression height is the distance from the center of the wrist pin to the deck of the piston (not dome)." flyguyeddy: were you measuring to the top of the dome, or the deck of the pistons? ('cause yes, I'm REALLY interested in this, maybe in a new 4th or 5th gen bike as a fun project) Link to comment Share on other sites More sharing options...
flyguyeddy Posted October 18, 2011 Share Posted October 18, 2011 yes we are referring to compression height of the piston. the 929's are a little taller than the vfr around the edges. i plan to chuck mine up in the lathe at work and cut off just enough to clear the squish zone in the head. Link to comment Share on other sites More sharing options...
woody77 Posted October 18, 2011 Share Posted October 18, 2011 Thanks for the clarifcation. :) I'll go back into lurk mode now... Link to comment Share on other sites More sharing options...
Veefer800Canuck Posted October 18, 2011 Share Posted October 18, 2011 yes we are referring to compression height of the piston. the 929's are a little taller than the vfr around the edges. i plan to chuck mine up in the lathe at work and cut off just enough to clear the squish zone in the head. ooh, pics please? Link to comment Share on other sites More sharing options...
Guest Posted October 27, 2011 Share Posted October 27, 2011 you will have to probably have to cut the valve pockets also when you cut the pistons. Link to comment Share on other sites More sharing options...
Guest Posted February 11, 2012 Share Posted February 11, 2012 Hey, this one dead in the water? Link to comment Share on other sites More sharing options...
flyguyeddy Posted February 13, 2012 Share Posted February 13, 2012 no its just stalled. i need to get my pistons machined and i havnt had the time. Link to comment Share on other sites More sharing options...
flyguyeddy Posted April 21, 2012 Share Posted April 21, 2012 Ok i have started to machine my pistons. As discussed earlier .030 needed to be removed from the areas that will interfere with the head. So i chucked each piston up in the lathe and centered off the area between the middle ring and the oil ring, using the ring land from the oil ring to center the face of the piston. Touched off each face, backed the cutter off and moved it in .030. Then touched off the side of the piston and went in .154" (as read on the dial of the crossfeed wheel, which means diameter not radius). I came up with this number by subtracting the vfr piston diam from the 929 diam measured above the top ring. After i finished that cut i then did an angle of 22.5 degrees (as close as i could measure the vfr piston to) out until it stopped cutting. The result is this. You can see the one piston marked with yellow paint. That area also has to have .030 removed from it and i will blend it all into the valve relief pockets in the middle. What do ya'll think? Link to comment Share on other sites More sharing options...
Member Contributer YoshiHNS Posted April 21, 2012 Member Contributer Share Posted April 21, 2012 Sweet. Was it a pain to get them to run true in the late?\ So just need to lap the top surface then? Grind or mill? Or both? Link to comment Share on other sites More sharing options...
flyguyeddy Posted April 21, 2012 Share Posted April 21, 2012 Here is a side view, with both pistons sharing a pin. Link to comment Share on other sites More sharing options...
flyguyeddy Posted April 21, 2012 Share Posted April 21, 2012 It wasnt all that hard. Ill post a picture of my setup being as im doing 8 pistons total. Link to comment Share on other sites More sharing options...
Veefer800Canuck Posted April 21, 2012 Share Posted April 21, 2012 Cool. What will your displacement be with this setup? Link to comment Share on other sites More sharing options...
Veefer800Canuck Posted April 21, 2012 Share Posted April 21, 2012 And what about the weight of the pistons vs the Vfr ones? How is that going to affect the balance? Link to comment Share on other sites More sharing options...
flyguyeddy Posted April 21, 2012 Share Posted April 21, 2012 836cc. Im hoping to not lose too much compression with the smaller dome. Link to comment Share on other sites More sharing options...
flyguyeddy Posted April 21, 2012 Share Posted April 21, 2012 Piston weights with pin and clips are vfr=224.75g and modified 939 minus coatings is 231.9g. Not a whole lot of difference, really. I imagine it wont matter. This was actually discussed in either this thread or the other big bore piston thread Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.