Strawboss Posted October 28, 2014 Report Share Posted October 28, 2014 Hello All, I am in the process of rebuilding an engine for a guy. It is an old Trinity built 4 mil with 70mm bore on stock cylinders and a Trinity IV head. I am having a problem getting the head gasket to seal up the coolant on the front side of the head between the cylinders (the area about the 1 or 2 o'clock position on the LH cylinder and 10 or 11 o'clock on the PTO cylinder. It uses a 0.030" copper head gasket which I annealed. I was trying to use Hylomar as a gasket dressing. When I took then engine apart it was previously sealed up with lots of what appears to be Toyota Sealant #102 FIPG and now I think I know why. During the rebuild process I removed the head studs and surfaced the cylinder head surfaces on an inspection plate with 220 sand paper wetted with WD-40 doing figures 8's and rotating the cylinders every 8-10 times. When I first put the engine together I used a thin film of Hylomar and the coolant poured out just during the fill (it did pass internal cylinder leakdown test prior to that) and I did use a new set of o-rings from McDermott (formerly Trinity). The head was three stage torqued to 20 ft-lbs in sequence and I oiled the studs before installing the nuts. I took the head back off and inspected the cylinder surface with a straight edge. It looks pretty good except on the LH cylinder at the 2 o'clock position I measure it 0.0025" low outside the cylinder liner to the outer edge of the cylinder (the liner is flat, but the aluminum is low). Everything else is pretty dang flat. When I removed the head and put a straight edge acrossed it, it was 0.005" low in the center on the head shell. So after much pondering I surface the head shell down (realizing it would make the domes stick out more) until it was flat. I then reassembled using some Hylomar and torqued the head back down. I pressure tested the cooling system to 15 psi for 1/2 hr and it was good. The next day I heat cycled the engine and after about 5 mins it was starting to leak coolant again in the same spot. So I removed the head again and measure how much the domes stick below the coolant sealing surface as shown below. See below pic So I am thinking the domes are sticking out to far from the head shell. These domes use a fire ring so I don't want to remove material from that surface (plus the squish is already at 0.034"). So I am thinking of machining some material off of the backside of the domes to make them sit lower in the head shell. My question is, how much do I take off? I am thinking 0.005" for sure so that it always has at least 0.005" of "clamp" on the domes. Or will the domes still be sticking out of the head shell to far? I have not called Harry at McDermott yet about this, but he did tell me to use a light film of Yamabond on both sides of the gasket during reassembly when I purchased the head o-rings and copper head gasket from him, I am just been reluctant to do that so far. I plan to call him later today when they are open. My thoughts on next steps: * Machine back sides of domes to fit better * Loosen cylinder nuts a little bit during the next head assembly and tighten head down first, then re-tighten cylinder base nuts. * Use Yamabond, Coppercoat, or Toyota Sealant lightly on the head gasket (both sides) * Should probably get a new head gasket again too Any other thoughts/recommendations? (besides Trinity sucks and get a new head!?!?!) What sealant do you guys recommend on the copper head gasket? Thanks in advance! Ryan Quote Link to comment Share on other sites More sharing options...
BANSHEE HP Posted October 28, 2014 Report Share Posted October 28, 2014 .034 is too tight Quote Link to comment Share on other sites More sharing options...
Surfrjag Posted October 28, 2014 Report Share Posted October 28, 2014 with a squish that tight and looks like the band is huge, I would want different domes anyways... next your going to be blowing out fire orings save yourself the trouble and do what you know you should do, call noss machine Quote Link to comment Share on other sites More sharing options...
BANSHEE HP Posted October 28, 2014 Report Share Posted October 28, 2014 And holy fuck is that squish band wide. Quote Link to comment Share on other sites More sharing options...
Surfrjag Posted October 28, 2014 Report Share Posted October 28, 2014 or driveline performance Quote Link to comment Share on other sites More sharing options...
BANSHEE HP Posted October 28, 2014 Report Share Posted October 28, 2014 We don't have a 70mm dome Quote Link to comment Share on other sites More sharing options...
Phelps Posted October 28, 2014 Report Share Posted October 28, 2014 wide squish bands pretty typical with oldschool domes huh? lots of power on the table with newer domes. be better to swap anyways. Quote Link to comment Share on other sites More sharing options...
Strawboss Posted October 29, 2014 Author Report Share Posted October 29, 2014 Talked to Dave at Noss. He doesn't like taking his domes over 68mm. He has done some 69mm, but doesn't have enough room for the sealing o-ring at 70mm. Sooooooooo............. Short of pretty much starting over with new jugs, I can get a 0.043" thick copper head gasket from Tony Doukas to increase the squish and machine these domes so they are closer to the head shell sealing surface (not sure how much compression drop that causes). Or maybe get a stock head and have someone chamber it and then use one of Tony Doukas fiber head gaskets. What you guys think? Quote Link to comment Share on other sites More sharing options...
Strawboss Posted October 29, 2014 Author Report Share Posted October 29, 2014 Looks like the 0.043 thick head gasket compared to a 0.030" thick head gasket will cost 0.52 in static compression ratio which isn't too terrible I don't think Quote Link to comment Share on other sites More sharing options...
m671054 Posted October 29, 2014 Report Share Posted October 29, 2014 Taller base gasket or will that f up exh window sealing with the skirt? What are your timing # at now? Quote Link to comment Share on other sites More sharing options...
Strawboss Posted October 29, 2014 Author Report Share Posted October 29, 2014 I haven't put a degree wheel on this thing. This started out as a simple top end overhaul because of burned up MAG side piston..... then I found bad crank..... then I found a mess inside of the clutch cover and trans. To be honest I am kinda sick of working on it, but I want it to be good for the guy I am fixing it for because he has a fair amount of cash into it. Pistons stick out the hole 0.043" and it uses (2) 0.020" base gaskets and a 0.060" spacer plate in between the base gaskets. Long rod crank with WSM pistons for 115 rods. Quote Link to comment Share on other sites More sharing options...
registered user Posted October 30, 2014 Report Share Posted October 30, 2014 (edited) i realize your just cleaning up someone elses mess but i never understood why guys push the bore out that big. doesnt make much sense. on hondas with the .010" metal head gasket ive had good luck with ultra black permatex. usually takes couple taps from a rubber mallet to get the head back off. might give that a try Edited October 30, 2014 by registered user Quote Link to comment Share on other sites More sharing options...
Surfrjag Posted October 30, 2014 Report Share Posted October 30, 2014 maybe you could use .030" base gaskets and then check port timming. copper spray on the headgaseket might work or at that point you can cut the head flat so it will seal properly 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.