NHC 250 head gasket problems...

[DW818]

Hello to all...was wondering if anyone could lend me some help/info about the old 250 Cummins.
I just got my first " green machine" a 1970 m818...picked her up for a reasonable price and drove it home about 300 miles...I developed a pretty substantial external coolant leak when I arrived home...so in the past 2 months I've overhauled the top end...new gaskets and a new set of injectors...new fittings and hoses...I had the heads done and pressure tested...made sure both the block and the head mating surfaces were free of defects and very clean and reassembled according to the tm and a factory Cummins manual...I was just able to take it out for the first run on the road today and it ran good... had good oil pressure steady 180 water temp....when I returned home and checked the truck over the rear head closest to the firewall was leaking a pretty good amount of oil down the block on both sides...it seems I may have just may have made my problem worse... Is there a place where I should start looking first to remedy this problem...I followed the manual and the TM meticulously during reassembly...Torqued the heads in the correct pattern to 285 ft lbs in steps from 25 to 100 to 200 then finally 285 that was the end torque value that the factory Cummins kit said to torque the heads to...Is there a possibility that after running it I'll need to re check the torque values?...Any help would be greatly appreciated... Thanks

 

[KenaAuto]

Are you sure it's not the valve cover?

 

[5tonman1971]

Just as a rule of thumb in my book, after assembling any engine allow it to get to operating temp and then let cool down and re check head bolts and anything else that gets hot and check the valves for correct lash.

i have yet to have to tear in to my trucks engined but as a mechanic this is what I do on all rebuilt engines.

 

[DW818]

I checked the rocker boxes and the valve covers and the oil leak is definitely coming from the head gasket...every so often at idle you can see some small bubbles form in the oil as it runs out...wasn't sure if I had to re-torque anything after I ran it a few times...or there is a problem with my liners...I inspected them as best as I could for cracks or abnormal wear but I saw nothing...no protrusion from the block either...

 

[KenaAuto]

I just had the rocker boxes off of mine, but haven't had the heads off so I can't give any advise on that. good luck, at least I'll bump up the thread.

 

[wrenchturner6238]

Well if you have a leak making a good mess re torque is not the problem in my opinion. Sometimes the rocker box gaskets mess up or the rocker shaft has o-rings in both ends (I have had trouble with these). The only other thing I can think of it maybe the inserts in the head gasket for the oil ports are missing some how. The head bolt holes can crack and leak too. There are repairs for that.

 

[DW818]

99.9% sure its not the rocker boxes...I can clearly see the oil is coming from between the head and block...weird part about it is I didn't have this oil leak before...just coolant....really hope my block or head didn't crack in the process of torquing the heads down...I made sure head cap screws had clean motor oil on the threads and on both sides of the washer when I installed them..before hand I tapped every hole in the block and the heads and blew them out really well with compressed air...all the threads looked and functioned as the should...really disheartening when you try and provide a little TLC for a nice old truck just to make the problem worse...thanks for your help .

 

[wrenchturner6238]

Yes you are right it almost makes you not want to do something like that!! If the oil is coming out right by a head bolt hole you may be able to or i have heard of this take the bolt out silicone the threads and re-torque. This would be a temp fix but may work. The Cummings head gaskets of old you had to put the inserts in the metal gasket before you installed it. I can not think of much more.

 

[wrenchturner6238]

I am thinking about your coolant leak was it running down the block like coming between head and block?

 

[DW818]

Yes ...back corner of the head...near the firewall...now its an oil leak for whatever reason...on both passenger side and driver side...I used locater studs to make sure the head was aligned with the block and gasket so there was no guesswork there...A friend at work told me of a dye at work that you add to oil and run the engine and I hafta remove the rear head again it'll show where its leak in from possibly...trying to do as much research as possible..and you guys on this site are a huge help thank you.

 

[wrenchturner6238]

Well to me it sounds like to me you did everything you could do for a good install. I am figuring that it is a gasket problem when you take it off inspect the O-ring inserts good. It would be a good idea to put dye in the oil and use a black light if you can.

 

[DW818]

I followed both the TM and the factory service manual meticulously...I tryed to do everything I could afford short of a complete in frame overhaul with new pistons,rings, liners and bearings...trying to keep this old girl around with out breaking the bank. Which I am now finding might be a little difficult...headed to Napa today to get some die...Hope I can get it the 2nd time around...

 

[WillWagner]

There is only one place pressurized oil runs through the gasket. It is in the center, just behind the center head bolt on the fuel pump side of the engine, between the two push tube cavities. If the leak is at the rear of the head, i would start looking above the deck, unless you used old style gaskets. If you used gaskets that required installing the water grommets, you should do the gaskets again. Try to NOT use the "cealastic" gaskets, silver color with a rubber strip around the outside edge of the gasket. Use the black gasket that has the white water passage grommets in the gasket. The gasket does not touch the head or deck. The only place the gasket itself touches anything is around the liners at the liner beads. The water grommets and oil passage area get squished only at the passages. A good way to tell if the gasket has sealed at the water passages is when the gasket is removed, 1/2 of the gasket will be on the deck, the other half on the head. No need to re-torque the heads. If there were any oil on the deck or you spilled any, it can and will get under the gasket and look like a leak. Use brake cleaner to spray the gasket area and run it to see what happens. Yes, there is dye available to find leaks.

 

[DW818]

Thanks for the info Will...I used a factory cummins gasket kit which indeed had the silver metal with the black rubber around the edge...and who ever did them before me must have used them as well..If it was the previous owner or the military I'm unsure...This is making more and more sense Because the front head had the better gasket with the white water grommets which stuck half and half when the head was pulled away from the block...and the middle and rear had the silver and black rubber...and the middle and the rear were leaking front was not...Who makes the gasket that has the white water grommets? and or where could I locate these gaskets? After I set the timing I poured a quart or less of new rotella t on the rack as a pre start lube before replacing the valve cover gaskets and covers. Would this oil have caused this leaking? With the engine at idle you can see oil seeping out at both the passenger and driver side rear corner of the head near the firewall..seems to be coming from right at the head gasket/head/deck mating surfaces...leaking enough to see it run down the block and drip off to the ground...enough to make two small puddles in 10 minutes of idling while inspecting where the leak is coming from...I'm gonna track some oil dye down ...spray the area down with break clean and take her for a spin up to operating temp tomarrow if the weather is decent...I'll let you know what I find...Thanks for the info/help everyone.

 

[DW818]

Is this the gasket with the white grommets you spoke of? Don't know if this pic is going to work...I found a set on ebay.

 

[WillWagner]

Yes, those are the correct gaskets. The silver gaskets work good on new components, but when an engine gets miles on it, they don't work so well. Oil leaks were the biggest issue with those gaskets. Timing? I hope you mean overhead set. If you are messing with timing you need special tools to set it up correctly. No need to pour oil on the rockers, the oil will get there fast enough from the inside of the parts. Lubing the outside does nothing.

 

[DW818]

Excuse my incorrect terminology... Yes I meant overhead set...Gonna grab these gaskets up and regroup for another teardown thanks for all the help.

 

[Carlo]

I once installed head gaskets backwards on a Pontiac and water leaked in the oil pan. Is there any way the gasket could be pinched or wrong? Do you have the heads checked for cracks?

 

[DW818]

Used locator studs to insure proper gasket alignment...studs were two of the old questionable head bolts that had some minor pitting on the shank of the bolt that I machined the heads off of to thread in the block to aid in alignment...put the remaining head bolts in and torqued to a low value then removed studs and replaced with the last two head bolts... made sure mating surfaces were clean and free of oil on both head and deck...made sure they were facing with the side marked "top" up and yes I had the heads checked at a machine shop...pressure tested...etc...I dont think I pinched anything considering the steps I took directly from the manual...but somethings gotta be up because I've got this oil leak/ seeping problem.

 

[DW818]

Update: Pulled an "all nighter" last night...Good friend of mine assisted me in getting the trucks top end torn back down to square one...I have observed a couple of things that seem out of the ordinary.. Really hoping nothing is wrong... 1. The injector plunger in cylinder #5 is stuck in the fully closed position!!! ...said to myself "Hmm, That doesn't look good." Finding #2 After pulling the rocker boxes, removing fuel cross overs and unfastening the head cap screws (according to the TM's loosening pattern) I found the end cap/plug from the rocker box axis sitting in between the rear and middle head!!It resembles a small freeze plug and goes in the end of the rocker box between the middle and rear rocker boxes...Not sure of the terminology on that... excuse me if I am off. I didn't notice till I was lifting the heads because the cap was sitting in the small area between the heads...As far as the head gaskets go...It seems that the water grommets didn't make a good seal because only a couple stuck the deck /head when removed...I'm arming up with a decent digital camera and heading back to take some photos to upload...Hopefully I don't have more problems with that hung up injector / Rocker plug issue...any input would be greatly appreciated... Thanks