Hi forum, currently fitting new liners and piston & rings to a 3T engine serial number 3T11667. I cannot find any listing in the parts book for the head core plugs. The engine was sitting for 10 years and was stuck (rust damage to number 1 & 4 cylinders) and had 3 litres of water in the sump. Engine still looks good on the bottom end but the heads need usual work like lap in valves, new precombustion chamber gaskets. Should I be checking or replacing the core plugs. The water manifold and water lines all look good with no rust eating away mating surfaces. Existing core plugs are steel.
Tried looking in SIS but keeps telling me no such S/N even with leaving out everything except the 3T and D7's in SIS only go back as far as D7E! Did some digging and seems the last #t Cat D7 was built in 1955 so I guess it's not surprising that Cat has not put it in SIS!
If you have a parts book look at the page for the 6F5317 cylinder head and valve mechanism group - field replacement (Page #34 in my parts book) shows a quantity of 8 plugs for two heads with a 3B0623 part number. I believe they are what you are after and yes I would replace them. They have been known to rot out.
Not sure why but Cat does not list plugs like those in the "Similar Parts Lists". But I would probably just pop them out and go to any good auto parts store and match them up. I did a Google search on that 3B0623 number and there are some people out there that think they are made out of silver dollars! I saw prices up to $10.00 each for them! Even Cat is only asking $3.10 for them!
The head assembly is a 1F9677. I am using the D7 form 8628 parts catalogue effective 7M4325 to 7M9999 and 3T1 and up. I checked on Old Magnets post in my parts catalogue and it does list plugs as 3B622 but only 4 (2 per assembly) which I guess would be two per head. I have an old head which is cracked down the shed and it has 8 plugs in the top about 1'' in diameter.
I'm using 3T1 to 3T1999 parts book form# UEO30775 (1969 printing). Says 3B0623 plug quantity 8 (4 in each 1F9677 assembly). Seems they are off with the count. Just like Cat to use an odd size plug to, measure carefully. I also have the Form 8628 parts book and it doesn't show the plugs at all. I looked at my 3T20000 to 3T28058 which shows a 6F5274 cylinder head with 16 3B0623 plugs (1/2 in each 6F5274) Looked some more. Your head shown in the picture is a part #6F5274, casting number is 6F4919. A 1F9677 head will have a 1F9672 casting number.
Thanks Old Magnet. The head pictured is an old head from the previous owner now only scrap. I checked the two heads off the engine I am rebuilding and they are the same casting number. Indeed 6F4919. You are a wealth of information. So these are not the originals as the engine I am rebuilding is number 3T11667.
Hopefully those plugs are a standard size. I would recommend replacing the steel plugs with the copper versions.
Brass or stainless steel might be the best materials, but if proper cooling system maintenance is done plain old steel should last for more years than the rest of the old dozer!
I would wait and see what the backsides look like, good coolant and a minimal amount of corrosion go back with original steels, and do not forget to put a sealant on the rim as you install them otherwise will weep. Horribly eaten up still put in steels but figure on a decent coolant filter add on or adding Nalcool or a substitute as needed to keep pH/chemistry under control. New conventional a-freeze has corrosion inhibitors but they deplete over time doing their thing, the additives replace those inhibitors.
Thanks everyone for your help. I have sourced some one inch brass core plugs in Australia. I will be smearing some sealant around them and running a good inhibitor/ coolant.