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B43M Cylinder Head Removal

2513 Views 6 Replies 5 Participants Last post by  tss8690

I am preparing to decarbon the heads on my B43M but have read that some have had head bolts break during removal. While I know that there's probably no sure fire method of ensuring that the head bolts won't snap if their frozen, I would appreciate any thoughts or advice before I start turning wrenches. I've read that in some cases folks have taken their motors to machine shops when a head bolt snaps. That's great if you have a reputable machine shop nearby, but my cursory search indicates that reliable shops who have mechanics who are familiar with Onans are in short supply in my area.

Many thanks in advance for your assistance.

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Hi Tim,
The bolts that are problematic are the ones that have been tapped all the way thru. This leaves them open to moisture from the other end. I suggest that you get some Kroil from Kano Labs, spray into the open bolt holes several time a day for several weeks. This will let the Kroil penetrate and hopefully prevent the bolts from braking. You will need to remove some of the cooling baffles to gain access to the areas that I have mentioned. Not all head bolts go all the way thru, you will need to find them with a mirror and flashlight. Perhaps someone here knows which ones and will comment. Been a while since I've done Onan maintenance all my engines are now Briggs & Strattons with overhead valves.
Mad Mackie in CT :mrgreen: :mowlawn:
Thanks Bob. I will look for those bolts and spray them with some penetrating oil or an equivalent solution. :thumbsup:

Hope all's well in CT. I'm originally from Mystic.

I think they all go thou below third cooling fin one between intake and exhaust port on top I would brake torque on it first. Using Torque Wrench in walk down removal good practice along with hand tools. While soaking going good time set valves on flat head engine any valve wear cuts valve open time reduces valve lash and engine power.
If this is any support, I've removed the heads on my B48M twice in 29 years of ownership and about 1,500 hours of use. The bolts came out without any problems. Carbon scraped out, new gaskets added and bolts torqued to spec with no problems. I wish I was a mechanic rather than just a DIY, but my 1982 model 448 is still running just fine.....where's the wood to knock on? Good Luck on yours. Mike
A warm/hot engine would help also.
Thanks everyone for your feedback. Still on the "to do" list but will let you know if I hit any snags when removing the heads. Replaced the points and condenser today and that's made a big difference. :grin:

Thanks again!
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