dickie wrote:Warkton Tornado No.1 wrote:The PX studs are inexpensive & an excellent rolled, marginally oversize thread & the longer threaded end can often be used to further increase the strength of their fit within the crankcase by increasing the depth of the M8 holes if you have no access to Helicoils. I torque the head to 22.5 ft/lbs & don't want to be worrying about the studs pulling out.
I've just ordered some MB ones as they're waisted and around 11mm longer than the ones I have. I had considered adding helicoils, but dismissed it as unnecessary. Maybe I should reconsider?
The theoretical maximum strength for thread depth in alloy is only about 2 x 'D' which is 16 mm, but we're talking about a decades old die casting that not only will have hardened through work & age, but will also have a large zinc content because Innocenti knew how to produce aesthetically pleasing products with minimal scrappage. On occasion, I have carefully drilled down 35 mm or more, particuarly when the proximity of the stud is so close to the transfer port that the only way to maintain strength is to go extra deep. I also dowel the cylinder to the crankcase because I am a fussy b@st@rd.....
As for the comparison of Piaggio versus A.N.Other's products, I think that the likelihood is that a manufacturer of Helicopters is likely to have far better Quality Control in place, & having witnessed problems with over length front sprocket bolts & rear hub bearings with plastic ball cages, I know where my faith lies.
dickie wrote:Warkton Tornado No.1 wrote:Stud length can easily be compensated for simply by counter-boring the cylinder head holes deeper. Hard, stainless, very thick M8 washers are available via eBay that can take advantage of a modified counterbore size. 19 mm diameter if memory serves.....
Ok, I don't think I'll need to with the longer studs, but just in case, how deep can I go? typically of course.
(See above)
dickie wrote:Warkton Tornado No.1 wrote:Compression ratio, & therefore volume needs to be safe, but ballpark figures are good enough & will hardly be affected by squish variation.
I'm trying to optimise here, so I;m going for a corrected ratio of about 6 or 6.2:!
As per Bell's tuning guide, I only see the logic in uncorrected (or geometric) as it makes perfect sense to me. If that is of any use though, I aim for 10:1 maximum.
dickie wrote:Warkton Tornado No.1 wrote:The squish is very important as the piston sheds it's heat by getting to within the closest distance practicable. I always aim for 1.0 mm & whilst that may seem a faff, it is worth it for the optimum results. But then again, I always centralise the head & barrel with either hollow dowels or pin dowels.
Yes, I'll be aiming for a similar figure.
Squish is often tricky to get spot on, & my 'cheat' is to VERY CAREFULLY achieve the best match of piston to head concentric ally after dowelling as close to it as possible by 'lapping' the two together. What I do is stick some abrasive wet & dry to the piston in the form of a ring (polo mint shaped) & lower it into the tightly assembled barrel & head. Then, with a lot of elbow grease accompanied with questions such as "Are we there yet?" the eventual result is a perfect match of profile.
Obviously, you cannot afford any abrasive to come into contact with the bore, so this is best performed prior to the final hone. Which reminds me, your bore could be better than it appears, IMHO. Sorry! It has took me years to eventually achieve a really good hone & the secret is to have a drill that goes REALLY slowly with loads of torque, & I have the Milwaukee Combi to thank for that.
dickie wrote:Warkton Tornado No.1 wrote:Head gaskets are prone to fail. Personally, I refuse to use them in any engine build as there is always a way in which you can achieve the desired geometry without having to employ them.
I need to get the head and possibly the barrel skimmed to achieve a decent squish, so I've no need for head gaskets.
Top Man!