• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Pistons

Share this page

Bob_Spidell

Bob_Spidell

Yoda
Country flag
Offline
Thinking about which pistons to buy form my BJ8 rebuild. 'Generic' sets run about $400 and look OK--as if you can tell by looking at pictures--and the top-of the line appear to be Denis Welch's forged pistons (at nearly a grand$). Are the forged ones worth it? Also, most 'stock' sets are 5-riing, and the DWR are 3. Obviously, the 3-ring would have less friction/drag than the 5-ring, but would the difference be significant in a mostly stock street car?

Also, any recommendations on brands or suppliers?
 
Forged pistons are a waste of money for a low-mileage street-driven collector car. What is wrong with your existing pistons? Replace the rings if you think they need replacing, but as long as the pistons are not damaged or the bore has been changed, keep the ones you have. Hone the cylinder walls to remove glaze and prevent oil burning/blow-by.
 
The engine will be bored (it's 30-over already). Also, I put up to 5K miles/year on this car; would that be considered low-mileage?
 
I have had great service from AE brand stock pistons. I agree with TimK, forged pistons are not the best way to go in a stock street machine. My understanding is that most, if not all forged pistons have a greater expansion rate so require more clearance in the bores = little noisier on cold start up until the engine warms fully. Ask your machine shop what they recommend - typically they would want the pistons selected prior to finishing the bores.

Buy stock pistons and spend your extra money on Total Seal gap-less 2nd compression rings. They really seal well. I haven't bought any for a few years now but it used to be possible to buy just the 2nd rings from them. I will not build another motor without them. I have had motors with 2 years of racing and 20k street miles still showing only 5-8% leak down (and I spend a lot of time between 4 and 6,000rpm).
Dave
 
AE, Nural, JE ... all good pistons, but where can I buy them (40-over or bigger, probably; haven't heard from the shop yet)? The only oversized pistons I've found are County brand ... don't get me started on them.
 
After having two of my personal engines both with failed piston rings in #6 piston I'm not sure that the stock material is good enough and maybe to better have forged pistons. I have overhauled engines for friends and a couple of them had piston ring failures too in #6 piston. The rings break and end up taking a chunk of the piston side with them with the rings being pounded into the top of the pistons. When someone says they can't quiet their valves by adjusting and have done everything they can think of its then that I suggest taking a look at the top of the pistons for pieces of rings.
 
Hi Bob,
I know JE is familiar with our engines, maybe give them a call and ask what they have, or can do? I know the second option could get pricey.
 
Tim, Dave & Greg all make good points, so not a lot to add...

I don't remember where I heard/read it, but you do not have to put a ring in the groove below the wrist pin, if you want to cut some friction__and you can use a 3-piece low-tension oil control ring in one or both grooves, instead of the high-tension 1 pc cast ring.

Eye candy...

IMG_5913.jpg


IMG_5973.jpg


IMG_5975.jpg


The smaller set of 100/6 pistons are in the car Jim restored, and the bigger ones are for Quick's 3000 (anybody heard from him lately?)
 
Bob_Spidell said:
The engine will be bored (it's 30-over already). Also, I put up to 5K miles/year on this car; would that be considered low-mileage?
Click to expand...
I understand that a rebore requires new pistons. And yes, 5,000 miles is low mileage, especially if it reasonable street mileage (not going to red-line with every shift.). I mentioned honing, because I rebuilt an MGB race engine (without a re-bore) with new domed pistons and rings (13:1 compression) and had instant blow-by because of glazed cylinder walls. Had to tear it down and hone it with my electric drill. Worked fine. A re-bore will probably be honed -- you need a slightly rough surface to bed in the rings.
 
Ok Randy's showing off the candy now...

Pistons & Rods.jpg

Detailed Crank.jpg
 
Back
Top