SuzukiSavage.com - Big Bore Engine - Part 6

DragBikeMike

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Re: Big Bore Engine - Part 6 - Test & Tune
Reply #15 - 09/22/20 at 00:43:52

The big engine has a very broad power band with no obvious “hits”. It just starts pulling and remains linear all the way through about 6800 rpm. It doesn’t seem to run up as high as the 94mm but who cares, it gets you to 7K so much faster. I have seen some comments on the forum to the effect that the 97mm won’t be much faster than a 94mm, it will just have better low-end torque. That’s not the case at all. It’s way faster than the 94mm, everywhere.

It has excellent manners. Idles great (much better than my 94mm). I attribute that to the cam. The 402 grind is a lot tamer than the 340b in my 94mm. The VM38, Mac header, and Stage III head all work well with the 402 cam. It’s like a different motorcycle. It feels like a big motorcycle now.

In terms of performance, I give this project an “A”. It was well worth the effort.

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DragBikeMike

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Re: Big Bore Engine - Part 6 - Test & Tune
Reply #16 - 09/22/20 at 00:45:27

I had to address the higher CHT. Other than drowning it with fuel there weren’t a lot of options. All the literature I have indicates this engine should run best with ignition timing retarded from the stock setting. The higher compression and free flowing components should require less advance, but the larger bore dictates a bit more advance. One book indicated that for a four-valve head with 100 mm bore, optimum total advance should be about 28° BTDC. My timing was set at 28°.

I tried advancing the ignition timing back to the factory setting (30°). The CHT came down quite a bit. It was definitely better. The looser engine probably helped too. Now the cruising temps were about the same as the 94mm engine. Long grades were better too. On the long grade, the CHT stayed below 340 and the oil temp didn’t exceed 230.

I still had the fuel mixture on the fat side. I guess I could live with that, but I would prefer a mixture closer to 12.5:1 at WOT and probably 13:1 at cruise. Once the oil leak is squared away, I will fiddle with the air/fuel ratio a bit more.

I decided that I would add an additional 2° of advance when I had the engine out of the frame to fix the oil leak. That might bring the temps down some more.

I removed the engine to repair the oil leak. It had 850 miles on the clock.

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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4162 Honolulu	Re: Big Bore Engine - Part 6 - Test & Tune Reply #17 - 09/22/20 at 00:46:02 The cam, springs, retainers, and cotters all looked fine.
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4162 Honolulu	Re: Big Bore Engine - Part 6 - Test & Tune Reply #18 - 09/22/20 at 00:46:44 And so did the rockers.
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4162 Honolulu	Re: Big Bore Engine - Part 6 - Test & Tune Reply #19 - 09/22/20 at 00:47:34 There was some discussion on the forum regarding the center oil-hole in the cam shaft. Would the smaller hole in the DR-based cam provide enough oil for the steady-bearing and cam chain? My 402 cam has the small #53 hole. The oil trough next to the steady bearing was topped-off and the steady bearing looked fine.
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4162 Honolulu	Re: Big Bore Engine - Part 6 - Test & Tune Reply #20 - 09/22/20 at 00:48:08 There was also a load of oil in the cam plug. No indication that there is a problem with oil supply in this area.
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4162 Honolulu	Re: Big Bore Engine - Part 6 - Test & Tune Reply #21 - 09/22/20 at 00:48:54 The tensioner had extended about 3.5mm, which didn’t surprise me. The chain and guides are new, so I expected them to bed in.
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4162 Honolulu	Re: Big Bore Engine - Part 6 - Test & Tune Reply #22 - 09/22/20 at 00:49:30 The 34mm intake valves are slightly longer than stock. I was a bit concerned about geometry. Looks like rocker geometry won’t be an issue. The wear patterns on the valve tips were perfectly centered. I think this will be OK.
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4162 Honolulu	Re: Big Bore Engine - Part 6 - Test & Tune Reply #23 - 09/22/20 at 00:50:02 Once I popped the head off, I could see that oil was being pulled through the entire joint. I suspect capillary action was at play. Oil was everywhere. And that Copper Coat spray sealant was LG (long gone). It even looked as if I had some combustion gas leakage.
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4162 Honolulu	Re: Big Bore Engine - Part 6 - Test & Tune Reply #24 - 09/22/20 at 00:50:35 The oil wasn’t just confined to areas where there was an oil passage. This is the right front corner. No pressurized oil here, not even splash oil, strictly crankcase vent.
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4162 Honolulu	Re: Big Bore Engine - Part 6 - Test & Tune Reply #25 - 09/22/20 at 00:51:17 Oil was even running down the left rear cylinder stud. That’s a normally dry stud, no oil close to it. So much oil reached the stud that the dowel filled up?????
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DragBikeMike Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 4162 Honolulu	Re: Big Bore Engine - Part 6 - Test & Tune Reply #26 - 09/22/20 at 00:51:56 The cylinder bore looked fine, and the piston had no evidence of seizure. Whew!!!
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DragBikeMike

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Re: Big Bore Engine - Part 6 - Test & Tune
Reply #27 - 09/22/20 at 00:53:14

All the cylinder head fasteners were tight. I estimate it took at least ~~120~~(typo) 220° of rotation on each 9mm nut to relax the fastener.

The sealant was gone. I won’t be using Copper Coat again. The other option provided on the Copper Gaskets Unlimited (CGU) instructions is Permatex Ultimate Grey. I have the Optimum Grey. It’s rated at a higher temperature. Maybe that will do the trick.

I checked the head and the cylinder for flatness. They were both well within the manual specification of .002”, but when I stacked the head onto the cylinder, I could just get a .003” feeler into the joint in the right rear corner. That could be a problem.

After pondering the dilemma, I decided to try the Optimum Grey sealant. If it’s not gonna hold when the surfaces meet the factory specs, maybe I don’t wanna run the copper gasket. The copper base gasket held just fine, and the copper one I’m runnin on the 94mm is leak free after many miles, but the head gasket looks like a different animal.

Here’s a look at a brand-new copper head gasket coated with a uniform layer of the Optimum Grey.

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Gskt_Sealant_Bott_Side2.jpg

« Last Edit: 09/25/20 at 23:21:45 by DragBikeMike »

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DragBikeMike

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Re: Big Bore Engine - Part 6 - Test & Tune
Reply #28 - 09/22/20 at 00:53:57

The process is tricky since the sealant must be tacky when you assemble the joint. Pretty hard to put a uniform coat on both sides of the gasket. So, I coated the underside of the gasket and placed it on the cylinder, then coated the underside of the head and placed that on top of the gasket. This is what the head looked like.

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Gskt_Sealant_on_Head2.jpg

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DragBikeMike

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Re: Big Bore Engine - Part 6 - Test & Tune
Reply #29 - 09/22/20 at 00:54:44

While it was apart, I took a good look at the head cover bolts along the right side. The right rear bolt was fine. The internal threads in the cylinder looked great. If you recall, I had a problem with the center bolt. The internal threads in the cylinder stripped, so I drilled through and installed a grade-8 bolt & nut. The forward hole had partially stripped threads, so I did the same repair to that fastener while I had the engine apart. It works fine. You can definitely put the squeeze on things with these grade-8 fasteners.

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