Force conrod connectivity to Chrysler

[Grtflashflyer]

Hi all.
I am new to iboats forum and I would like to post a question, greatly appreciate any feed back.

Brief: Recently had my 1978 85hp Chrysler Charger pulled down for a rebuild, it was due for its final at 3.352 .040 oversize but received a call from machinist that the middle cylinder was out of round and already at this size, so in an attempt to get more out of the block it was pushed out to 3.375. Ordered pistons had rings fitted then found out the pistons were top loading 19.5mm piston pin variety (Force 1996 and up). Not suited to my connecting rods at all.

The connecting rod for this piston is 6mm longer and requires 29 wrist pin bearings not 26.

Q; If I purchase Force con-rod # 640N O.E. #640-9612A7 with pin needles #010-136-29, lower rod caged bearings #010-150, will this application fit my crank. So, there lays the question, is the crank circumference the same on a 1978 85hp Chrysler as it is on a Force 75 - 90 hp of the year 1996 and up.

Many thanks.

 

[Frank Acampora]

Re: Force conrod connectivity to Chrysler

First off, there is a real problem in punching out the middle cylinder to 3.375. Although some Chrysler four cylinder and later Force engines used this bore size, it was with a completely different liner. At .040 over, your 3.3125 cylinder liner was dangerously thin. At .060 over there will not be much left at all and while it may run and give good service, it may also fail. There is a real danger of exhaust port webs warping under heat, protruding into the cylinder, and causing catastrophic ring failure.

The correct option to fix the block would be to either replace the block or have a specialty shop bore out the old liner and insert a new one. Yes, while cylinder liners are cast into the block, they are sold and can be replaced--expensive though.

HOWEVER: Since you have already overbored, the piston you want (I don't know part numbers) is the 3.375 piston for Chrysler 140 and early Force engines with a 3.375 bore.

Later Force engines after 1994 used a 3.375 piston but as you found out, the con rod is longer. The wrist pin hole is larger and higher up in the piston. The crankpins are also a larger diameter and the big end of the rod is larger and uses longer rollers. However, the rollers are the same diameter and number. SO: The newer rod will in all probability NOT fit your crankshaft. Additionally, the rod costs as much as a piston so you might as well buy another piston

ALL force engines in this class used a 2.80 stroke EXCEPT the 125 which was 2.875 for both Chrysler and Force.

By the way: Did your machinist NOT advise you of possible results of such a large overbore? Has he ever done outboards? They are different than auto engines.

 

[Grtflashflyer]

Re: Force conrod connectivity to Chrysler

Hi Frank, thank you for your rapid and thorough answer. First of all, in relation to my decision to exceed sleeve tolerance, I made this rash decision entirely on my own and have been warned of the likelihood and probable outcome by both my marine mechanic and machinist. However, I move forward (ignorance). To combat the potential heat and warping threat I will run a 110 degree thermostat and fuel mix at 40/1 with retarding the timing.

The boat and motor is used for fishing and family cruising on the lake, by no means stressed. With this in mind I, hope for a smooth couple of years motoring. (boating).

Based on your feed back. I, believe it to be in my interests to count my losses on the pistons and purchase the bottom guided piston (Wiseco 3151PS 3.357 17.5mm pin) and continue at own risk.

Kind regards;

 

[Grtflashflyer]

Re: Force conrod connectivity to Chrysler

Hi all.
Just a note in relation to exceeding over-bore tolerance. With further research, and phone calls, I was able to determine that my motor has had a re-sleeve done on its last rebuild by previous owner. The sleeve was 3.563 outer diameter with a length of 5.510, this was an oversize sleeve, therefor, after my current re-bore of 3.375 I am left with a sleeve wall thickness of 3/32 which I believe is still in tolerance.

I will attach photo's, If anyone can comment on these specs it will be appreciated.