13 replies to this topic

[Java_Green]

It seems like I am lacking usable crankshaft, conrods and pistons for my supercharged built. From what I can tell, it looks like there have been water standing in the engine (1275 A+) causing pitting marks in the bores (fabric mounted sleeves) as well as in the bearing surfaces on the crankshaft. My intention is to change the sleeves but the crankshaft is most likely beyond repairable and the conrods are missing. The engine will most likely deliver a substantial amount of power (>130hp) but will not be a screamer (rev limted to <6500rpm). Unfortunately my pockets are not endless and I do find available crankshafts and especially conrods - costly!

 

My intention is I-shape conrods. First thought was 1.75 inch big ends and standard small ends, but there is a lot with 1.625 inch big end conrods and matching crankshafts available. (I could not understand why... From my point of view larger big end bearings would lead to larger area to transfer load) So what would be suitable conrods and crankshaft? Is there any less costly alternative worth considering? (I am not located in a country where it is easy to find these parts second hand)

 

[hazpalmer14]

Standard con rods and crank are fine the sort of power you're after. Only thing I'd do is fit ARP rod bolts. If you can find a 6581 crank they're supposedly toughened from factory and we're fitted to some metro turbos not all, but also a standard crank will be more then up to the job.

[Steve220]

Standard A+ rods and standard crank are sufficient for almost 200bhp. But as above, ARP rod bolts are a must.

[Java_Green]

Standard A+ rods and standard crank are sufficient for almost 200bhp. But as above, ARP rod bolts are a must.

I do share your opinion about what the standard A+ crankshaft and rods could cope with considering power and torque. I guess second hand market is the place to find these items or am I wrong? The crankshafts are for example advertised by MS but have been out of stock for some time now. Standard A+ rods, I have not found.

[Hpal]

Put a wanted ad on here, someone will have a set. I've bought a new A+ crankshaft from minisport, and good secondhand a+ rods from a gentleman on the forum. I intend to hone the little end and fit floating pins and teflon buttons. and fit new arp bolts and get the rods checked over for straightness, and maybe a close and hose on the big end if needed.

[Steve220]

Be careful of second hand rods - make sure the pin was removed properly, and not with a blow torch and a hammer. I've seen 'mint' rods and found some that are twisted or bent.

[Java_Green]

I have digged out a set of pre A+ conrods. They seems to be in good condition. Will they be fine for the purpose and will they go with a A+ crankshaft?

Edited by Java_Green, 18 September 2022 - 08:19 PM.

[timmy850]

Like anything, measure them, check them for straightness and signs of heat

Get some arp fasteners and get the big end resized

[Java_Green]

Like anything, measure them, check them for straightness and signs of heat

Get some arp fasteners and get the big end resized

Is the big end size different between pre A+ and A+?

[nicklouse]

 

Like anything, measure them, check them for straightness and signs of heat

Get some arp fasteners and get the big end resized

Is the big end size different between pre A+ and A+?

Not as simple as that. 1275 are the same 998/1098/850 are the same and the you have the S.

 

but the comment has nothing to do with size. But with being correct.

[mini13]

1275 a+ rods are the lightest factory rod and up to any abuse youll throw at them in a turbo motor, the std a+ rid bolts are actually pretty strong, but most people fit arps for price if mind.

[timmy850]

Like anything, measure them, check them for straightness and signs of heat

Get some arp fasteners and get the big end resized

Is the big end size different between pre A+ and A+?

Resizing the big ends involves checking the bore that the bearing shell is clamped by, that it’s the right diameter to crush and hold the bearing under the load of the specific fasteners you are using.

They normally do this by removing a small amount or material from the rod cap and honing it to the right spec

Have a read through here:
https://www.theminif...izing-big-ends/

[Java_Green]

It is 1275 con rods in a supercharged application (not a screemer <=> <6500rpm) I am after.

1. Will pre A+ conrods withstand the abuse?

2. What is the weight difference compared to A+?

3. There is a lot of "meat" on the cap (pre A+). Could it be lightened to the extent to match the A+ conrods without jeopardizing the strength?

4. I it worth going for forged steel conrods?

 

I am well aware of that whatever conrods I am using, I need to check them thoroughly. 

[mini13]

theres a whole section in vizards tuning the bl a series but,

yep a+ rods will be fine, I've seen them used up to 8k

cant remember the weight difference, but the majority is in the cap, you can remove that, if your going all out then pre a+ rids are slightly better material, and if you can get them, innocenti rods are better still,

however, by the time you've gone through the agro and expence of resizing, balancing etc... then it may be worth looking at after market rods,