MartyHorse 4 #1 Posted March 21, 2019 Brought home a nice P220G recently with 700 hrs (Toro/WH 520h). Started and ran great w/ no smoke, 120-psi per side compression, was happy with the $485 spent. Overall the motor was fairly clean and virtually no rust anywhere. Decided to pull the heads off for a look and started with the RH side. I loosed all 9 bolts and noticed that 2 of them were hard coming out, which was a little suprising since the cylinder threads were aluminum. The 1st hard one I tried to get out snapped after coming out about 3/8" (much more suprised then ofcourse) should have stopped when I felt it put up resistance. The 2nd hard bolt came out a little easier but started to tighten-up after coming about 3/4". So reversed it back in, then back out and seemed to get a little a further but it still has a long way to go. So I did not bother trying the other 'easy' ones yet. The last head bolt I snapped was on a 40 year old Japanese diesel, w/ cast iron block and heads. Why are these bolts putting up such a fight? I'll be happy to try and extract the one broken bolt, then just call it a day and forget about getting the heads off at all. Or to keep going, would it help to use PB blaster or something on the pain-in-the=@$$ bolts? -thanks. Share this post Link to post Share on other sites
Ed Kennell 36,468 #2 Posted March 21, 2019 I hope not, but Is there any sign of a liquid thread locker. I would try some heat on the block to break them loose, then soak with PB or Kroil and work them in and out to get the penetrant down the threads. Is this the front or rear head? Share this post Link to post Share on other sites
squonk 39,552 #3 Posted March 21, 2019 You have steel bolts and aluminum block. Different rates of expansion. I see more broken bolts in AL than steel or iron. The threads gall and seize up more than a rust issue. Only thing I've ever seen worse is stainless steel. 5 Share this post Link to post Share on other sites
lynnmor 6,961 #4 Posted March 21, 2019 If you feel any resistance, start soaking with PB, it may take days. If any bolt holes are open on the back side, spray PB there as well. 4 Share this post Link to post Share on other sites
MartyHorse 4 #5 Posted March 21, 2019 18 minutes ago, lynnmor said: If you feel any resistance, start soaking with PB, it may take days. If any bolt holes are open on the back side, spray PB there as well. Thanks. 1 Share this post Link to post Share on other sites
peter lena 8,206 #6 Posted March 21, 2019 those dissimilar metals will get you every time, ask jeep about their rust issues. i agree with the others above ,soak and slowly work it , back and forth, spray and repeat . pete Share this post Link to post Share on other sites
MartyHorse 4 #7 Posted March 22, 2019 Thanks for all of the advice. I'm soaking them in PB. I understand the corrosion issues between aluminum & steel. I've taken heads off several motorcycle engines with longer, thinner bolts -- never had this much trouble. You'd think after building these for 10+ years, Onan would have known by then and installed high-carbon steel ones. The bolt that snapped was cheap and I seriously doubt that it was really grade 8 as I've heard claimed. It just twisted in half. High quality head bolts tend to 'shatter'. Share this post Link to post Share on other sites
lynnmor 6,961 #8 Posted March 22, 2019 Does the bolts have the six lines on the head? chart Share this post Link to post Share on other sites
