What fails in strokers

[RenoF250]

I picking parts for my build now and I am wondering what is the weak point in a stroker. I have not read about many had mechanical failures, mostly flat cams, valvetrain issues etc. Has anyone seen piston, con rod, or crank failure on a stroker? I plan on building a fairly mild 4.6. Reliability is important but I don't want to spend big money on forged rods if the cast ones work fine.

[akadeutsch]

I have the same Question. Just how much Horse Power can the stock 258 rods handle? Do I need forged rods or a forged crank?

[Cheromaniac]

I have not read about many had mechanical failures, mostly flat cams, valvetrain issues etc.

That usually sums up the biggest chunk out of the stroker failures. Most have been rebuilt to fight another day.
Bottom end failures on a stroker are almost unheard of and the few that do occur are usually caused by oiling issues.

[vashxj]

i have only seen cams fail but even with that there is a lot of variables from each build. This is just my opinion but the cam failing could but from incorrect pushrod length, springs, valves, break in, oil, or even the machine shop not getting the bearings in right (unless you did it yourself).

[akadeutsch]

My machinist told me that connecting rod bolts are the week point on the bottom end of the Jeep 4.0, but I have never heard of them failing.

[Cheromaniac]

My machinist told me that connecting rod bolts are the week point on the bottom end of the Jeep 4.0, but I have never heard of them failing.

Α new set of ARP 112-6001 rod bolts would be cheap insurance against failure.

[Wombat Ranger]

^^ That's one thing I wish I had done with my engine. New main bearing and rod bolts. Probably not going to have issues with them since it's such a mild build, but if I were to do it again I would do that. Oh well.

[RenoF250]

^^ That's one thing I wish I had done with my engine. New main bearing and rod bolts. Probably not going to have issues with them since it's such a mild build, but if I were to do it again I would do that. Oh well.

I am not too worried about the bolts they are grade 8 and the caps are cast. My dad used to drag race (13s kind of cars nothing crazy) and he said he always reused rod bolts and so did everyone he knew and none broke that he was aware of. Grade 8 is strong stuff.

That are lots of places you can buy "cheap insurance" on engines but $50 here and $100 there pretty soon it is not so cheap.

[Wombat Ranger]

Good to know, thanks Reno.

[RenoF250]

I think we could add cooling problems to this list. I was talking to a part/engine shop guy last night and he said they had one of the IC944s seize in #6 because of expansion. They had 0.0045" but recommended more on the back three to prevent. Then I read a similar story from someone else. I was planning on the IC944s but now I am leaning more towards the dish hypers.

After thinking about it a bit I see now why everyone is running the FC water pumps. Coolant goes front of the head to front of the block, the only flow in the back is what does not make it through the passages in the front. At idle with a stock pump that is likely not much.

[jeepxj3]

I thought it flows out the thermostat housing?
WP--to block--out the back of the block to back of head--across the head to the front--out the thermostat--to the top or the radiator--out the bottom to WP...

Or do I have it backwards?

[superstingray77]

2 Failures I had were caused by improper building.
1st engine the head builder setup the springs at much to high of a seat pressure and it destroyed the cam.
2nd engine the seller of my forged pistons had us hone the walls too far .0055 + .060 which caused the pistons to rock in the bore and tear up the skirts on 3 of the 6 holes.

1st combo- had rebuilt stock 4.0 rods with ARP bolts and IC944's. They are still like new condition sitting in the box.
2nd combo- has K2 forged rods and had AutoTec (505 perf) forged pistons/pins.
3rd combo- I will have AutoTec/RaceTec make the pistons for me to the final bore size (likely .080) but this time we will use the MANUFACTURER recommended piston to wall clearance of .002-.003 max. The newer forged pistons have CNC cut skirts vs. the older forgings that had skirts cut manually on a skirt cutter and human machinist. This and the advances in alloys mean you no longer need the excessive P/W clearance that the forged slugs 5-10 years back required. I may also see if I can have the skirts coated for additional safety margin.

Lastly I have heard this from a vast # of sources NOT to ever run a Melling HV pump again. My last engine snapped the oil pump drive shaft (separate issue from the piston to wall problem) the reason for this is the additional load (wasted horsepower) side loads the input shaft to the the oil pump as well as slowly tearing up the cam/distributor drive gear. The tiny metal filings along with the heat generated where the oil pump main shaft enters the pump allowed it to literally weld itself to the inside of the upper pump housing. Upon tear down the gears inside the pump were spotless, and despite my driving it another mile off an overpass with no oil pressure all of my bearings were fine.
So for me ONLY standard volume pumps.

[SilverXJ]

I thought it flows out the thermostat housing?

That is correct

WP--to block--out the back of the block to back of head--across the head to the front--out the thermostat--to the top or the radiator--out the bottom to WP...

Sort of correct. There are cooling passages all through the head gasket, so it isn't 100% pushed to the rear and the rear will see decreased flow.


I'll add to this list cam bearings. I had a nasty fight with them and a few others did as well.

[RenoF250]

I thought it flows out the thermostat housing?

That is correct

WP--to block--out the back of the block to back of head--across the head to the front--out the thermostat--to the top or the radiator--out the bottom to WP...

Sort of correct. There are cooling passages all through the head gasket, so it isn't 100% pushed to the rear and the rear will see decreased flow.


I'll add to this list cam bearings. I had a nasty fight with them and a few others did as well.

That seemed like the direction it should go but did not seem right for the pump. Anyhow, the front of the engine has a very short water flow circuit, the back only gets the coolant that is left and has already run over all of the other cylinder linings.

What happened with the cam bearings? How can those go bad? They have the easiest job in the engine. What do I need to watch for there?

[RenoF250]

2 Failures I had were caused by improper building.
1st engine the head builder setup the springs at much to high of a seat pressure and it destroyed the cam.
2nd engine the seller of my forged pistons had us hone the walls too far .0055 + .060 which caused the pistons to rock in the bore and tear up the skirts on 3 of the 6 holes.

1st combo- had rebuilt stock 4.0 rods with ARP bolts and IC944's. They are still like new condition sitting in the box.
2nd combo- has K2 forged rods and had AutoTec (505 perf) forged pistons/pins.
3rd combo- I will have AutoTec/RaceTec make the pistons for me to the final bore size (likely .080) but this time we will use the MANUFACTURER recommended piston to wall clearance of .002-.003 max. The newer forged pistons have CNC cut skirts vs. the older forgings that had skirts cut manually on a skirt cutter and human machinist. This and the advances in alloys mean you no longer need the excessive P/W clearance that the forged slugs 5-10 years back required. I may also see if I can have the skirts coated for additional safety margin.

Lastly I have heard this from a vast # of sources NOT to ever run a Melling HV pump again. My last engine snapped the oil pump drive shaft (separate issue from the piston to wall problem) the reason for this is the additional load (wasted horsepower) side loads the input shaft to the the oil pump as well as slowly tearing up the cam/distributor drive gear. The tiny metal filings along with the heat generated where the oil pump main shaft enters the pump allowed it to literally weld itself to the inside of the upper pump housing. Upon tear down the gears inside the pump were spotless, and despite my driving it another mile off an overpass with no oil pressure all of my bearings were fine.
So for me ONLY standard volume pumps.

You are making me nervous, your 2nd combo is exactly what the seller of the IC944s is telling me to do - give .005 - 0055 clearance. I thought the worst that would happen is piston slap noise, I don't need a skirt problem.

Is this a misconception on the pistons sellers part in both cases? I was looking at the Keith Black site and apparently you need to cut the top ring gap bigger than recommended by the ring vendor. Do you think the seizures they saw were from the rings and not the pistons?

Why didn't you just change the cam the first time? How many miles did you get on it? How much did you hone for those pistons?