Jetboater Pop

Just thought I’d let you know how the “ overhaul “ ended up. After removing the head I Dropped it off to be reconditioned. It was an L18 head so had bigger exhaust valves. The old valves had recessed badly so there was no valve adjustment left on some. 4 new valves and seats all done , skimmed the head slightly. All came back nice and shiny and I reassembled it . With the help of my mechanic freind we pulled the pistons , rods etc. He was really impressed on the condition of the engine even after all these years. Then over the many weeks I stripped and cleaned, polished etc everything. We honed the bore ( stock size bore and rings) and slightly removed an area for the larger exhaust valve on the edge of the bore as described in Crash’s post. New seals , gaskets rings and bearings and carefully reassembled. Set the timing etc , cam chain position etc, primed oil pump and filter and she was ready. Pulled plugs and cranked to get oil pressure up , plugs in and she started first pop.Bolted back up and fitted heat exchanger etc and other bits that jet boats have. Took it down to the local lagoon a few times to do the “run in “ process . What a difference. It goes like a cut cat , Clean instant start , way more power.Crisp is the word. Really pleased with the outcome so many thanks for your help. Got to say it’s been a great experience and considering we did this on an old kitchen table in the garage I’m impressed with the finished product. Cheers again , Paul. Ps if I can get a photo up I’ll do it soon as it looks as mint as it goes.

Thanks once again Crash and Mike. That info is exactly what I was after, cheers very much :thumbup: .I will follow those instructions when I get the head back and give it a hone. Hopefully when its running I will put up some pics.

Yep thats exactly it Crash.Thanks for putting up a pic..Am I right in thinking that the valve has tapped that little half moon mark (always wondered why I couldnt adjust out that tapping noise ). So am I right in thinking that I should remove a small bit of the area where the mark is ?(descrouding i ll have to google that ) :blush: . Im unsure if the head will need resurface as it may have been done previously. already on 2 notch . i ll have a chat to a mechanic mate who is going to help me.Im after reliability as much as anything as I go up rivers miles from nowwhere and you cant paddle back so street race performance is not essential.A bit crisper ,responsive would be great. Many thanks again , cheers, Paul.

Cheers for the replies guys. Ive had the engine for 25 years..old fella...so when I got it i dont know what it came out of other than I was told its an L16. The original heads long gone. Cylinder width is L16 size so thats how i know its an L16. The newer head has larger valves than an L 16 also A87 on the side so I assume its an L18 . I got the L 18 head from an engine shop probably 15 odd years ago and its been on the engine till now. The marks were present on the edge of the block when the head was removed. maybee it is a gasket imprint.Its been a long time since fitting Pistons have a slight dish to the middle. Im taking the head to a machine shop to get the new seats fitted. should I get it shaved to help with a slight raise in compression?.as for posting up a photo i havent looked into that as Im not that flash on a computer :confused: , rather have a spanner in my hand. Doing rings and bearings at the same time while the heads at the shop. Anything else i should look at ? .Many thanks again.

sorry to drag up this old thread but I have anL16 engine and an A87 L18 head. Can I fit it without fear of the exhaust valve hitting the edge of the cylinder as the bore size on the L 16 is slightly smaller.??? Or is my thinking totally wrong.

Good morning people. I have been using your forum for a while now , its been a great source of info for me. I have an unusual set up , no car but a 12ft jet boat powered by an L16 Datsun engine.Pretty rare these days Id say. so ive joined in the hope you can answer a question for me. I replaced the standard head a few years back with an A87 head. The valves adjustments were running out , I had no adjustment left on some cylinders so I pulled the head. some of the valves are have recession so need to get new seats and a couple of new valves etc. Now what I have noticed on the exhaust side of the cylinders on the top of the block is a small half moon mark .Ive no idea what caused this. Its as if the valve has been just tapping ? the edge of the cylinder?. So im trying to figure out what caused it. I had a thought that the A87 head (the valve size is bigger than the L16 ) and Im sure its an L 18 head on the L 16 block may move the valve postion out a tad so that it possibly hits the very top edge of the cylinder?? or am I totally wrong. Can the L18 A87 head fit straight on to the L16 block with no issues or am I stuffed. A big question for a first post but ant help would be appreciated. Cheers, Pop.