t90 glow plugs

[owen]

i have bought some new g/plugs for my t90 from asap. unfortunately they seem very tightso much that it is virtually imposible to screw them in. the old ones were a good fit but nothing like this. asap speciofy only one plug.anyone else come up against this any advive gratefully received

 

[bdsweeting]

Without predjudice to the makers but I wasn't that impressed with the quality of the threads when I changed my g/plugs recently - Ford 1.8l.

Try adding a small amount of oil to the threads of the old plugs and work it into the thread bit by bit to clean out the hole/threads.

The repeat the process using anti-seize grease on the new plugs; this may help to clean and recut the threads on the plugs and in the holes.

 

[tonykerry]

I have replaced the glow plugs on my T90 with those from ASAP and the new ones made a world of difference to the engine starting. (I also checked the compression of each cylinder while I had the glow plugs out, the diesel compression tester was borrowed from a local diesel garage).
When I had removed the glow plugs I inserted a drill (I think it was eleven sixyfourths of an inch from memory, but I could check when I next go to the boat) with grease on the cutting edge, turned it by hand to cut through the build up of carbon in the glow plug bore, extracting it regularly to clean off the carbon that it had cut through. This made the task of installing the new glow plugs easier, especially with a smear of grease on the threads.
With the new glow plugs installed the engine panel ammeter will go to full discharge initially, but then comes back to a more reasonable figure. Best of luck, Tony Kerry

 

[oldharry]

Almost certainly carbon in the head threads. Need to be cleaned out using a thread chasing tool or with a little care a standard tap of the correct size. Also be careful that the debris does not fall into the cylinder - use plenty of grease on the tool, and withdraw it frequently to remove the carbon as you work it in.

 

[dickh]

Do as tonykerry says - measure the thin tip, find a drill marginally bigger and just turn it by hand so the tip hole is reamed out.(I suspect the ASAP tips are slightly larger than the originals fitted - mine unscrewed easily but the new ones wouldn't screw in by hand).
Also use the drill mentioned to clean the seat which gives the gas tight seal. Also if you can borrow a tap of the correct size(M10 x 1mm pitch), grease and clean up the thread. Then use a copper based grease to prevent seizure in future - AntiSeize; Copper-Seize or similar product.
Just done this myself(albeit with the head on the bench) and the new (ASAP) glow plugs go in easily.
Incidently the ASAP glow plugs are half the price of Thornycroft ones!

 

[T_S]

Cant see a boat diesel being that much different to a car engine or bigger. Thing is if the glow plugs unscrew ok then the new should go back in without to much hassle, the only question I have to ask is :are the glow plugs O.E equipment?

My profession as a motor engineer I have never encountered this problem when replacing glow plugs, normally they can be a bit of a bugger on the initial releasing but once the torque has been removed they unscrew by finger, they normally screw back 'home' by finger too.

I would difinately not use a drill or tap either if the thread was damaged!
A thread cleaner would be my choice of tool to use.

But before risking damage to the cylinder head first check that the glow plugs are Original Equipment.

 

[owen]

thanks for the replies. i will try with the recommended 11/64 drill bit to clean out the carbon.the new plugs are copies as the original champions are out of production. the actual tip looks to be he same size as the original so i am not sure why the original goes on so easily while the new one is so tight.