Cheap 1750 big bore kit for 356 - drawbacks?

[Burma-Shave]

I am in the states next month and am thinking of picking up a barrel and piston set for my C.

Big bore kits at £300 are pretty tempting, vs the stock mahle kit at about £800 ( but dont you love the weak dollar? )

I know the maestro wasn't averse to these kits, but that was 20 odd years ago. Surely if I get everything balanced, should be OK?

[Timo]

Go for shasta, they're supposed to be the best. not sure how much tho.

[Burma-Shave]

Cool, that rings a bell.
Found this too:
http://www.912registry.org/tech/bigbore.htm

Talks about NPR being the standard back then.

Al zim has repros of the NPR set for £200!! (and mahle for £600..)
http://www.allzim.com/acatalog/Piston_a ... _86mm.html

[40 scout]

Johnny - judging from your video - u don't need no kit !!!!!!!!

Steve

[Burma-Shave]

Thanks Steve.

So,we stripped her down and it already has the big bore kit..explains a lot! I'll post up a separate story once Mike B has finished checking her out, but so far looking healthy enough.

[cubist]

Cheap B+Ps are great if you keep it serviced properly (unlike me...) and a giveaway price too

[40 scout]

There you go again - CHEAP - go on dig deep in that sporran - treat yerself!!

Nice to see the sterotype alive and well -

Steve (Off to the pub for another soft southern shandy)

[hot66]

I'll post up a separate story once Mike B has finished checking her out, but so far looking healthy enough.

that must be a relief . Car did seem to go well in Scotalnd.

[Mike Holloway]

Burma-
THERE IS NO SUCH THING AS A FREE LUNCH!!!!
Years ago, when the 'first generation' of NPR's were current, we often saw engines that were 'drinking and smoking' alarmingly, after 20,000 miles or so.
Upon stripdown, we were astonished to find piston to bore running clearances of about four thou., but no ridge at the top of the bore, and no ovality to speak of. Not only this, but the ring groove clearancees were all over the place: some too big, some too small. Subsequent asking around amongst friends in the trade revealed that I was not the only one to find this. ( Either Harry Pellow. or Craig Richter mention this in their various books).
The simple fact is, or at least was, that the machining accuracy was crap. They were effectively brand new copies of knackered barrels and pistons.
The barrels themselves were made of Gorgonzola cheese- they would suffer from an effect known as 'washboarding'. This is an effect whereby the bore becomes a series of ridges up its length, due to the fins on the barrel providing greater support to the bore than the area in between the fins. The material itself was simply not strong enough to resist this effect.
I cannot say that this is the case with the current NPR's, But for sure, they are not going to be anywhere near as good as genuine Mahle items.
As for sets of barrels and pistons at £ 200, words fail me!
Get real!!! They are only fit for use as doorstops!!
If you want your engine to last, Bite the bullet, and buy QUALITY!
TO PAY CHEAPLY IS TO PAY TWICE!!!!
Good Luck in any event!
Regards
Mike Holloway

[Burma-Shave]

Damn, the voice of reason!

Thanks for the valuable insight Mike, you obviously have loads of experience in this area, and I appreciate your help
..I am a little torn, I would rather do things right, but I don't want to lose the torque that the kit clearly bestows on my 'damen' motor, and at this price I could go through 3 sets in place of one mahle set (that 60k miles, then!?). There is some other stuff (like one of the pushrods being odd, a welded valve carrier) that I am making sure gets replaced too.

Also the motor apparently shows signs of being set up for the kit - ported intakes, bigger carbs..and I expect has the correct head clearances? (On the outer limit of my knowledge envelope here.. ) - so I thought it would be happiest replacing like with like.

The current p and c are not in bad shape actually- a little off-round on a couple, a little bit too much ring movement on one. Accounts for a little bit of smoke I suppose, as do the missing valve seals. There was no washboarding, though. We're mainly replacing because the heads are off, kit is so cheap and I happen to be in the states next week. I know that big bore kits are known to sacrifice a little oil use for more power - my 912 was the same.

Zims were a little reassuring when I asked them about the kit (they could have pushed their Mahles at me if they wanted) They are also a very long running company.

Zim's guy said-
Thank you for your email regarding our
"low-in-price, yet high-in-quality" big bore sets.
We have been carrying this particular brand for about a year and a half now,
and the quality seems to be better than the previous versions of big bores -
including the original NPR. These are substantial enough for spirited
street driving and possibly low level vintage racing. We have many sets in
the field, and have also sold a couple of the forged version sets, which are
made by the same company.

Forged pistons are stronger, but in a 90hp engine they are really not
necessary. They also cost quite a bit more ($929) and only come in 9.0:1
compression ratio. We have to special order them, which takes a couple of
weeks.

I guess I could consider the forged set but I'm out of time on this occasion.

Now I've got the valuable help of Mike B, who is a mere three hours drive with my engine in the boot of the Merc..(!), I think I am happy to give this kit a bash in the first instance, and as a field testing service to DDK!

(Edit: I think the crazy US prices are a little distorting, too. UK suppliers sell the BB kit at over a grand..)

[Mike Holloway]

Hi Johnny-its me again, the prophet of doom!!!

You have to realise that I am a somewhat cynical old sod when it comes to mechanical refurbishment in general; my experiences of NPR stuff was back in the early eighties: I suppose that it is reasonable to suppose that they have generally developed and improved their products over the past quarter century!
The trouble with aftermarket stuff for engines is often more to do with lack of consistent quality than poor quality materials and design per se:
some people had no trouble with the old NPR's, bearing in mind the price of them compared to Mahle.
All things considered, budget priced aftermarket are probably worth a go, so long as you don't mind the possibilityof having to chuck them away after a rather short service life. At least they can't do as much damage as knackered old pistons with rings slapping up and down wildly in their grooves!
I still think that a set of original Kolbenschmidt cast barrels, bored to 1720, with J&E or Shasta pistons to suit, would be the best solution, but it does involve a fair bit of general messing around, as compared with simply buying everything new..
Your remarks about your pushrods is a bit worrying: Porsche made several permutations of pushrod, using both aluminium and steel, in various combinations. The principle behind this was that the pushrod expanded at the same rate as the barrels, thus maintaining correct valve clearances in any given engine. Ask your chosen supplier of new barrels & pistons what their recommendations for pushrods are in this respect: if they seem vague and confused about the subject, think twice before buying their product!
I am not sure what your reference to a 'welded valve carrier' is, but again, it sounds very alarming! Mike Bainbridge will sort it out, I am sure.
If you need any replacement engine internals, let me know- I may well have whatever you want, for dirt cheap!
In the meantime, good luck with it all!!
Regards
Mike Holloway

[Burma-Shave]

Mike, the die has been cast! Parts are ordered!
I have ordered the BB kit from Zim, and the exhaust valve guides and gaskets I needed.

The pushrod and valve carrier gear I have ordered from EASY in California.
Pitured beneath - there were 7 of the lower style of pushrod and 1 of the upper style! I just sent them this pic and asked them for one of the lower ones..Mike mentioned the differential expansion rate too. As long as theyre all the same and keep my valve clearances right, should be OK?



This is the valve carrier I meant. I should have said Rocker arm support, I suppose. Got one from Easy for $25, better than $500 from Stoddard . Easy are another old-time company that are well known in the 356 registry, so hopefully I won't get another welded one!



Maybe I'll go for the bespoke big bore plan next time, sounds good. I guess I am buying both parts and knowledge at this stage..I'm really enjoying the learning curve.

[Graham]

Make sure the rocker support you get is aluminium and not the short lived magnesium one's.they break!

[Mike Holloway]

Dear Johnny- first of all, Graham from Dartmoor is right about the rocker pedestals- magnesium ones make excellent paperweights!
As regards your pushrods, you have made a bit of a tactical error here: The basic idea is to use pushrods that expand at the same rate as the barrels, thus maintaining the correct valve clearances. If you have cast iron barrels, they will not expand as fast as an aluminium pushrod, especially as they are securely held down on the crankcase, and, of course, the pushrod is free to expand as it pleases. The net result is that the valve clearance will close up, which, if the clearance was too tight in the first place, could lead to yet another wallet punishing experience.
Ideally, you want a full set of 'A' steel pushrods, but, if it is too late to change your order, the steel/ally/steel pushrods will be okay, unless you absolutely nail the throttle for extended periods. But then, you are not a 356 hooligan, are you??
One small tip about the 3 piece pushrods; the steel ends are known to work loose over the years, so check them out by carefully gripping one end in a vise with fibre jaw covers, and some similar arrangement at the other end, and check that they are good and tight on the ally centre section.
You can, of course, buy aftermarket chrome moly 'DIY' pushrod kits, whereby you cut the tube to the required length, and press in the ball ends. These are very strong, but heavy, and are generally only needed for competition work, but may be worth considering; if you do not know the history of the engine, you may possibly find that the heads have been refaced more than the standard 0.25mm or the valve seats have been refaced so many times that the valve stem is poking out the top too far. Both of these things will decrease the distance between the cam follower and the rocker arm adjusting screw.This can mean that you adjust the screw so far that it cuts off the oil supply into the rocker arm, resulting in yet another kick in the wallet.
Ask Mike Bainbridge to check these things out, as it would not be best practice to use your old pushrods in such circumstances. The only dodge, to avoid buying DIY pushrods, is to shim up the rocker pedestal. This lifts up the pedestal from the cylinder head bolts on which it locates, making positive location somewhat marginal. It ain't nice, so keep your fingers crossed that your heads have not been butchered in the past.
I shall await developments with bated breath....
Mike H.

[Burma-Shave]

you are not a 356 hooligan, are you??

I have emailed Mike B, as he knows what shape the heads are in. Ive seen the cromoly 'rods, and could easily pick some up next week too.

The rocker stand was specified in Aloooo-min-um, yes, not crumbly magnesium.

Thanks for ongoing tips, Mike H! Another day at school today, then..