Shinniu sn25 running hot

[Rich Waugh]

$10.00 is awful cheap for a head gasket, even a two cylinder one. Are you sure it is the correct gasket for that engine? Diesels run high compression and need good quality head gaskets; generally steel is used for the cylinder rings at a minimum.

Bad idea to use Loctite on head bolts - interferes with the proper torque readings. Torque specs for bolts, unless specified otherwise, are for clean, dry threads. Bolt and hole, both. You can look up on the internet the torque specs for the size bolt you are using. Be sure to be exact - diameter and thread pitch. That will put you in the ballpark if you can't find the torque specs from the engine manufacturer. No gasket goop on the head gasket, either.

You do know that heads need to be torqued down in a proper sequence, right? Usually, though not always, it is started in the center of one side, the opposite bolt, then the next bolt on the first side, then the opposite, etc, working your way to the ends. I usually torque the bolts in sequence to about 30# less than max, then go over them again in sequence bringing them up to full torque. Others may do it differently.

The head should probably be checked for flatness. You can do this yourself if there isn't a machine shop nearby that can do it. A sheet of thick plate glass (3/8" or so) and some feeler gauges will tell you a fair amount and if you have a machinist's straightedge you can check it completely. If it is out of flat by more than .005" I'd have it milled flat. You can also have it checked for cracks while you're at it.

 

[jonyyuma]

Some diesels do use sealer on the head-bolts......To seal the threads, and most definitely have a pattern to tighten the bolts down in set values at increments...Hard to believe it does not have steel in the gasket at the cylinder, also $10.00 is very cheap?

 

[Shenniu SN25]

Haven't had the head checked, guess it could be warped or have a crack didn't see anything obvious when I had it off... I did torque it from the middle out alternating sides. I'm pretty sure it's a m16x2 stud they were torqued in two step increments to 146ft lbs i also assumed it was a grade 8.8. Gonna take it back apart this weekend if the head fix in a bottle doesn't work, don't got a lot of faith but worth a shot, dumped some bars head sealer in it just to see if I get lucky. Suppose to let sit overnight and flush the system tomorrow. I let everyone know what fixes it.

The gasket came from sun ray tractor in Ocala fl they had two in stock so I got both! Was gonna upload a pic of the gasket but not sure how to using my iPhone through the app. If interested I can send it through email.

 

[Diamondpilot]

I am no expert, never changed a head. But 146 ft lbs seems like a lot. I just rotated the tires on both my trucks and my trailers yesterday. One truck calls for 140 ft lbs, F-350 diesel. The other calls for 105 ft lbs, Nissan Titan. Both trailers called for 120 ft lbs.

Maybe I am way off but these are wheels studs that take extreem forces. I can not see a head needing that much but what do I know?

Chris

 

[Rich Waugh]

I'm not at the shop so I don't have it written in front of me right now, but it seems that 118 lb/ft was the torque setting for the head bolts on my TY395 engine, if I recall correctly.

 

[greg_g]

Y85 engine too. Book says head bolt torque range 150-170Nm. That converts to 118 ft-lb (+/- 7 ft-lb)

//greg//

 

[Rich Waugh]

Over-torquing a fastener can be as self-defeating as under-torquing. If you torque a bolt past its yield point it will stretch, but not recover, and then no longer holds tightly. In so doing, the gasket is crushed past the design point and when the bolt yields the gasket is now not properly compressed and leaks. Odds are, on a Chinese casting, you'll strip out the threads before you over-stretch a bolt, but that's not a sure thing, either.

Without knowing exactly what size and alloy the bolts were I can't say if they've been over-stressed, but if they have been then they have to be replaced with new ones.

 

[Smalljobs]

Be sure to use a torque wrench of high quality and the correct size so that your readings are in the middle of the wrench range. Using an old beat up borrowed wrench with a bent pointer is a recipe for problems. When I retorqued the head on my Jinma for the first maintenance milestone, I borrowed a high quality click type wrench from a mechanic friend in a reputable repair shop.

 

[jonyyuma]

I agree that the bolts do stretch, sometimes they cannot be reused. Thye moght can be measured for stretch, if in doubt replace. There is no sinking feeling like when a bolt gives on the last adjustment..Your setting of over 150 lbs. sounds to be very high.