45 replies to this topic

[Retroman]

Slightly off topic but    Even cams can be out

 

We helped a guy recently, running a weber he had massive stand - off at certain revs [ petrol 'cloud' ouside the carb ]

 

and torque was way down on what was expected. After a lot of checking, head scratching, measuring and remeasuring

 

The cam that was ground wrongly with different LCA's on different pairs of lobes...Ultimately meaning the timing was probably only correct on 1 cylinder ??

 

I have recently known crank journals to be 2 thou tapered which came down to an uncalibrated grinding machine.

Precisely why I haven't used 'that place' for the last 35 years despite them being the nearest, could give you a long list of horrors from the 'that place'. PM me for a forewarning.

 

Its safe when engine building to assume nothing and check everything twice at least, and that includes your own measurements

 

Nick has the right idea....that way its their responsiblity,  [ be it an engineering shop or engine builder ] to do the engineering and make sure its correct as they build it. By keeping it "in house" makes so much sense for any customer, it may not be the cheapest route but cheap is never usually good. It only needs one small mistake or mismeasurement and an engine and gearbox can be toast. ATDATT [attention to detail all the time] not quite OCD but near.

   I was reminded of this recently when running a MINIstox race motor on the engine dyno....mine ran perfectly and another guys was not even fit to run, the flywheel bolt having been over torqued and damaged the crank, his pigeon never ran, mine flew.

[cal844]

Ministox, don't get me started on them haha, changing rules a week before a big meeting which meant I stripped, reshelled, new thrust washers and rebuilt an engine in 3 days(from the car driving into and out of the garage)

Edited by cal844, 08 March 2019 - 10:45 PM.

[Retroman]

I know of a few horror stories like yours Cal, we have done a few 18 hour working days and 2 am finishes before meetings.... changing regs during a season is seriously wrong, they are bu***rs, but it their rules.

 

It's hard work now as I am sure you know, the regs are now really tight in an attempt to keep speed and cost down....but the cost saving doesn't work as you end up chasing small increases at huge cost.

  

Hillclimbing / Sprinting is best as the regs are so open...same engine block in same end of the car...the rest is free...simples, it could be argued that it comes down to budget, but if you know what you are doing the really big money boys can have red faces...love it.

[nicklouse]

  

Hillclimbing / Sprinting is best as the regs are so open...same engine block in same end of the car...the rest is free...simples, it could be argued that it comes down to budget, but if you know what you are doing the really big money boys can have red faces...love it.

but that does depend on the class. you do need a twink in the mod prod class now as they can easily add an extra 50 BHP over a 5 port.

[Inno]

 

thanks a lot....so if I really would like to be precise and sure I have exact clearances I shall do everything on the crankshaft and lower part, buy new bearings and then do the measurement with dummy pistons in order to be able to decide which pistons to use....and how much to skim the deck (or pistons) if needed to achieve wanted CR....

 

To be really precise you need the new bearings on a refreshed crankshaft.  It should be checked with plastiguage on each journal to make sure the bearing clearances are good. [Yes machine shops get it wrong] The crank end float should aslo be checked [a dial guage is best] and set at what matches your application, the bottom end is then sorted.

 

Decide which pistons first....they depend on what the engine will be used for and budget

 

Then dry build / measure / skim [block, head and or pistons] to get the CR needed...

 

Which again depends on existing condition, engine use, fuel and camshaft.

 

Not sure what grade of fuel is available in Zagreb ?

 

I plan to buy set of micrometers and a dial gauge - do I need pastiguage in this case also?

 

What shall be my journal clearances and crank end float clearance? - road use around 95HP and same torque, balanced crank and A+ or Innocenti 1300 conrods - think they are identical dimensions. No plans to to drive at 7000 rpm all the time but would like to be sure eveything is in place if I do .

 

But the big question for me is the one why I started this thread - can I buy pistons without knowing my possible deck clearance?

 

I understood that if I do not know possible deck clearance ( at TDC) it may be risky to buy pistons and risk they are too high if the block was skimmed before. - there can be only small amount or none material to skim from pistons in that case.

 

I guess can't be a problem if they are too low (TDC) since I can skim the block and the head if needed but again I loose volume.

 

I aim to 9,7:1....and pistons +20, 1310cc - with pistons that have 6cc dish  if my pistons ends up same level with the deck I need 28cc chamber and it looks a lot.

8cc dish means 25cc chamber and again a lot of grinding.

 

Expanding chambers may be done but no clue how that impact overall performance and chamber efficiency?

 

What is maximum but efficient capacity of the chambers that can be obtained from 1270 A+ head?

 

I can get fuel 95 and 98.

 

Thanks!!

Edited by Inno, 10 March 2019 - 11:24 AM.

[Inno]

 

 

I've done the floating pin conversion in the past and the teflon buttons work well with full skirt pistons, where the gudgeon pin length is close to the diameter of the bore.  Ever done it with slipper type pistons, where the pin is much shorter in length than the bore dia.?  Building an engine atm and considering this mod but the pistons are the slipper type.  Prefer floating pins over press fit every day of the week.

 

 

Yes, I have done them with AE Pistons (when I was still using them) and Hypertecs.

 

I don't make them a tight fit in the Pin and I also drill an off set vent in them. If the vent were done on centre, it would get blocked off on the wall of the bore.

 

If you are concerned that there's too much hanging out, make them in Aluminum.

 

I was checking floating pistons but they are more expensive .....although this looks as a fair deal:

 

http://www.minispare...-STN103-20.aspx

[Inno]

I have a set of linished down pins which are about 0.0005" smaller diameter.
These make the trial build very easy.
And yes, remove the rings from the new pistons before doing the trial build, but do it carefully. It is so easy to snap a ring and you cannot buy them individually!

thanks

[ACDodd]

It's quite normal to run 24 to 27cc chambers to get the CR correct. You need to do a trial build to work it all out. I sell dummy gudgeon pins if you need a set to help with your trial (dry build). Available as a set of 4 or singles.

Quite honestly there is no problem using press fit retention gudgeon pins in your build. The people that have had problems have not ensured the correct interference fit in the rod when they report that they come out. They also overheat the rods during fitting, and affect the temper of the steel. This also loosens the fit.

Ac

Edited by ACDodd, 10 March 2019 - 11:57 AM.

[Inno]

It's quite normal to run 24 to 27cc chambers to get the CR correct. You need to do a trial build to work it all out. I sell dummy gudgeon pins if you need a set to help with your trial (dry build). Available as a set of 4 or singles.

Quite honestly there is no problem using press fit retention gudgeon pins in your build. The people that have had problems have not ensured the correct interference fit in the rod when they report that they come out. They also overheat the rods during fitting, and affect the temper of the steel. This also loosens the fit.

Ac

Thanks for the clarification...think I red somewhere that chamber capacity shall not go over 25cc.......... and in case pistons are flat with the deck I would need 28cc....worst case scenario.

 

If 27cc is doable and still keep good function and efficiency of the chamber I think I am more or less on the safe side to buy any piston I would like to.

 

What crossed my mind now is if the chamber goes to 27cc wouldn't that actually make more breathing space around valves and have positive results in any case?

 

 

Thanks again

 

Hrvoje

[Spider]

 

 

 

I've done the floating pin conversion in the past and the teflon buttons work well with full skirt pistons, where the gudgeon pin length is close to the diameter of the bore.  Ever done it with slipper type pistons, where the pin is much shorter in length than the bore dia.?  Building an engine atm and considering this mod but the pistons are the slipper type.  Prefer floating pins over press fit every day of the week.

 

 

Yes, I have done them with AE Pistons (when I was still using them) and Hypertecs.

 

I don't make them a tight fit in the Pin and I also drill an off set vent in them. If the vent were done on centre, it would get blocked off on the wall of the bore.

 

If you are concerned that there's too much hanging out, make them in Aluminum.

 

I was checking floating pistons but they are more expensive .....although this looks as a fair deal:

 

http://www.minispare...-STN103-20.aspx

 

 

You can go to Pistons that have clips, but, they tend to be more expensive and really, for no reason other than 'a performance part' tax. The Nippon Rings these are supplied with doesn't take heat too well at all. Many I've seen end up quite soft to the point that they can be tied in knots. It appears they are soft to start with for a short break in period, and it's likely that which leads to their short life.

 

The factory never recommend heating a rod to fit the pins, if that is done, you have no idea how well the pin is griped by the rod after fitting and the temper of the rod is lost.

[Inno]

what about those pistons and rings:

 

https://www.med-engi...ast-pistons-040

 

 

comparing to SWIFTUNE:

http://www.minispare...-STN103-20.aspx

 

OR

 

http://www.minispare...40.aspx|Back to

 

(think same rings as SWIFTUNE)

 

OR set of those

 

http://www.minispare...60.aspx|Back to

 

 

price range is from 220 to 340 for a set so I can squeeze in any of those sets in to the budget...

 

please help...

[Spider]

For me, I'd really need to have one of each to check and recommend, however the last on on the last, I wouldn't recommend for anything.

 

In regards to Piston Rings, I usually buy (or try to) Pistons without Rings and then buy the Rings I want separately. It is a little dearer, but I end up with the Rings I want.

 

ACL & Repco (if you can find them), Grant, Hastings, NOS Hepolite or AE (in the Yellow Box) are all good rings. They are available in a few different types, ie, plain, cast and with various types of faces, though, a flat face is all that's needed for most applications.  Thorntons are the 'go to' people in the UK for Rings and for some Pistons.

[Cooperman]

The best rings I have ever used, although they are expensive, are 'Total Seal' rings. They are made in Phoenix, AZ, and have a gapless second ring.

 

My friends in air racing in the USA use them in their Lycoming engines.

[Inno]

The best rings I have ever used, although they are expensive, are 'Total Seal' rings. They are made in Phoenix, AZ, and have a gapless second ring.

 

My friends in air racing in the USA use them in their Lycoming engines.

Thanks.....guess a bit above my budget and objectively a bit above my intended use....sure can't go wrong with them but already went far out of build budget and need to balance all components quality and price vise to avoid overspend for one component if others are not even close to be able to use benefits of the most expensive one

[Inno]

For me, I'd really need to have one of each to check and recommend, however the last on on the last, I wouldn't recommend for anything.

 

In regards to Piston Rings, I usually buy (or try to) Pistons without Rings and then buy the Rings I want separately. It is a little dearer, but I end up with the Rings I want.

 

ACL & Repco (if you can find them), Grant, Hastings, NOS Hepolite or AE (in the Yellow Box) are all good rings. They are available in a few different types, ie, plain, cast and with various types of faces, though, a flat face is all that's needed for most applications.  Thorntons are the 'go to' people in the UK for Rings and for some Pistons.

ok...so if I would like to keep the budget and avoid being relocated permanently to my garage (by my wife ) I shall stick to a set and if consider Swiftune may have questionable Nippon rings same as minispares, the solution is MED Omega Die Cast with related rings....