Hopefully I'll be using a MPI block - if I can ever sort out how to convert it from auto to manual
| ausmini https://www.ausmini.com/forums/ |
|
| Shortening Con-rods https://www.ausmini.com/forums/viewtopic.php?f=2&t=50730 |
Page 1 of 1 |
| Author: | miniobsessed [ Sat Feb 28, 2009 6:08 pm ] |
| Post subject: | Shortening Con-rods |
I'd like to shorten a set of AEG521 rods to suit my stroker crank (86mm) so I don't have to machine so much off the piston crown and may actually achieve a reasonable CR. Has anybody had experience doing this or could anybody see any problems with shortening my rods by 1.5 - 2mm? I'd hope they would still be strong enough so I don't end up having to fork out for a whole new engine/gearbox. Thanks |
|
| Author: | drmini in aust [ Sat Feb 28, 2009 6:33 pm ] |
| Post subject: | |
Just remember the pistons will go down even further, possibly fouling the dizzy driveshaft, even if you thin it down. |
|
| Author: | miniobsessed [ Sat Feb 28, 2009 6:37 pm ] |
| Post subject: | |
Hopefully I'll be using a MPI block - if I can ever sort out how to convert it from auto to manual
|
|
| Author: | simon k [ Sat Feb 28, 2009 10:33 pm ] |
| Post subject: | |
miniobsessed wrote: Hopefully I'll be using a MPI block - if I can ever sort out how to convert it from auto to manual
does the how-to on auto-manual conversion in Mini Mods apply to MPi blocks? I'm not up with all the ins and outs of strokers, but by a reasonable CR, do you mean you want it lower because strokers usually end up with too much compression because they've got less dish on the piston after the crowns have been machined? surely it'd be easier to make the chambers in the head bigger, and a better shape to boot? |
|
| Author: | TheMiniMan [ Sun Mar 01, 2009 2:17 am ] |
| Post subject: | |
I wouldn`t shorten the rods at all,,, the best thing you could do is to actually lengthen them (or rather just buy longer ones) rod to stroke length ratio is more important than just making a piston fit. Just machine some off the tops of the pistons instead... & if you need some more volume then rip into die grinding the chambers out a bit too,,, de-shroud & shape & then pollish them , make them all even & you`ll have a nice engine |
|
| Author: | miniobsessed [ Tue Mar 03, 2009 4:05 am ] |
| Post subject: | |
Unfortunately, converting the MPi block from auto to manual does not seem as easy as the earlier blocks. I bought it thinking it should be a straight forward enough process but it's proving difficult. If anybody could help I would greatly appreciate it 
Matt - I remembered reading DV somewhere saying to fit "x" piston into an a series block it was necessary to shorten the rods. But I've just gone away and done some reading on rod stroke ratios and by shortening the rods 2mm I would only change the ratio by 0.024 (5.75" rod length = 146mm. 146/86 = 1.698 and 144/86 = 1.674). Would this make a huge difference? It does seem that a higher rod stroke ratio is better from a friction point of view and cylinder scanvenging but then also provide less torque and lower port velocities... Is this anywhere near correct??? Or am I missing something vital  it wouldn't be the first time 
I s'pose a little background on the rest of the bits wouldn't go astray either... I plan to use a 45 DCOE weber on a 5 inch minispares manifold (what I've got laying around), long 3 into 1 big bore extractors with free flow exhaust, head has been fairly well worked over with bronze silicone guides and rimflo valves (MK I S sizes) which I also plan to run 1.5 roller tip rockers on, Wade 176 camshaft (about 300 degree from memory), adjustable cam gears, 86mm crank, 'S' rods, MPi block (hopefully) which apparently has better load bearing main bearings (like metro turbo), blah blah blah... I've spent a lot of money (when it was available to me  ) getting to this point but my money tree is all but dead now that I'm a poor uni student after all these years... I'd really just like to sort these few problems I'm having and put it together so I can actually enjoy it I'm not saying I want to take shortcuts (this has been 4 years in the making already) but hopefully you can understand what I'm getting at...
Sorry for the novel and cheers for your replies
|
|
| Author: | drmini in aust [ Tue Mar 03, 2009 6:36 am ] |
| Post subject: | |
I wouldn't bother with the MPI block, I would use an 1100S one. Manual or automatic, no matter. Plenty about, and they are not dear either. I would leave the rod length standard and deck the pistons. I have an 84.33mm stroke crank in the 1412, we only had to take 1.5mm off the top of the 73mm Hypatec pistons. You could take more, no problem, the same goes for GR's new pistons. 
|
|
| Author: | mickmini [ Tue Mar 03, 2009 7:51 am ] |
| Post subject: | |
drmini in aust wrote: I would leave the rod length standard and deck the pistons. I have an 84.33mm stroke crank in the 1412, we only had to take 1.5mm off the top of the 73mm Hypatec pistons. You could take more, no problem, the same goes for GR's new pistons.
Mine is more or less the same, but with 10 thou less stroke due to the journal needing just a bit more grinding to clean up. Again it has standard length rods, a bit less off the top of the 73mm Hypatec pistons with a bit of a dish added to get the CR to 10.9:1. GR is a fan of the stroker because of all the torque you get from this set up. Face it - due to the crazy UK road tax laws of the 1950's all A-series engines undersquare. Less than ideal if you want to rev it to buggery, but that is unnecessary if you do the rest right. cheers michael |
|
| Author: | miniobsessed [ Tue Mar 03, 2009 10:14 am ] |
| Post subject: | |
OK... What would be considered a 'safe' piston crown thickness? |
|
| Author: | miniobsessed [ Thu Mar 05, 2009 8:34 pm ] |
| Post subject: | |
Thanks for the replies guys! Any more insight on this? Sorry to bug everyone but I just want to get this stuff sorted
|
|
| Author: | TheMiniMan [ Thu Mar 05, 2009 8:49 pm ] |
| Post subject: | |
no less than 5mm is my "rule of thumb" Just check em, but i`m sure they`ll be ok to lop some off the top, measure it all, work out what you need off & just do it 
|
|
| Author: | miniobsessed [ Thu Mar 05, 2009 10:53 pm ] |
| Post subject: | |
Cheers Matt 
|
|
| Author: | TheMiniMan [ Thu Mar 05, 2009 11:04 pm ] |
| Post subject: | |
you`re most welcome,,, & if you have any reservations or questions then please don`t hesitate to ask,,, i`m only tooo happy to help,,, i love strokers to the moon & back
|
|
| Page 1 of 1 | All times are UTC + 10 hours |
| Powered by phpBB® Forum Software © phpBB Group http://www.phpbb.com/ |
|