MT-FUEL-CORP Posted September 5, 2015 Share Posted September 5, 2015 Hello all,I'm new to the site .. thanks for having me.I've owned an 86 R 688ST for 5 years now. It's been converted to a fuel truck by the previous owner.It has an EM6 237 engine with a 10 speed transmission. The truck has been used as a storage tank for my diesel fuel. I have the bug in me to get her going again. The engine starts and runs. I have taken her out in the past week for a few 30 minute drives. I changed the filters and oil.Here''s the issue...I think she has a stuck exhaust valve. I can hear a tapping sound at low idle.It seems to go away (or I can't hear it) when I increase the RPMS. How can I diagnose this?Any ideas on what else it might be.Thanks BOB Quote Link to comment Share on other sites More sharing options...
chief doug Posted September 5, 2015 Share Posted September 5, 2015 try adjusting the valves, it could be a loose valve seat- very common, could last for years like that Quote Link to comment Share on other sites More sharing options...
Maddog13407 Posted September 5, 2015 Share Posted September 5, 2015 yup try adjusting the valves. does it have a Jake? if it sounds like the Jake is stuck on , 237's and 300's were known for wearing the valve guides out from excessive Jake use and it sounds like the Jake is stuck on at idle or when you let off it. Quote Link to comment Share on other sites More sharing options...
MT-FUEL-CORP Posted September 5, 2015 Author Share Posted September 5, 2015 No jake on this truck...yet.I've never adjusted the valves on a diesel. I have done so on older Chevy 350.Is it the same procedure?Valve cover off with the engine running? Quote Link to comment Share on other sites More sharing options...
chief doug Posted September 6, 2015 Share Posted September 6, 2015 no, cold engine- there are cyl numbers on the balancer. 2 per line. only do the one the pertains to the valves no down then turn to the next one. if you do it like a car there will be no compression. I learned that my first time. Quote Link to comment Share on other sites More sharing options...
b61mack Posted September 6, 2015 Share Posted September 6, 2015 You may not have a 237 unless someone switch it sometime. a 237 would be a R685, being you have a 86 it might be a 4 valve head and a R688 might be a 350 sense it has a 10 speed. do you have a 4 valve head, I don't think I have seen a 4 valve 237 Quote Link to comment Share on other sites More sharing options...
MT-FUEL-CORP Posted September 9, 2015 Author Share Posted September 9, 2015 The engine might have been switched out because when the dealer runs my Vin it comes back to a 350.I read the engine plate and it clearly says...EM6 237...manufactured in 1982.Kinda sucks that the original engine was swapped out....it is what it is.I'm just learning about these Macks...just gotta fix the tapping noise.Bob Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.