+4 mil stroke with OEM cylinder questions

[Bowtie316]

ok it must be a cr500 thing then. these cylinders arent very consistant. last one i had i used .060 gasket which put the boost at 130 then i brought up the transfers to match. got another cylinder and with .060 gasket it puts boost at 132. guess ill probly try a thinner gasket. what upward angle does your cylinder have on the front and rear transfer ?  i got fairly steep on the rear and more flat on the front . trying to raise the jug with gaskets so i can change them angles

I don't have a way to measure the transfer angle, but I would guess around 15° upward angle.  I don't really have any intention of changing the angle, just want to match the bottom of the ports to the top of the piston and clean up the crankcase side a little bit.

[udontknowme]

you sound like you have a good handle on what your doing. but heres something in case you werent aware. lets assume your roof is 15* and the floor is 15*. when you drop the floor down 2mm, if you simply just lower the window and slightly inside the tunell , then youll also reduce the floor angle as it enters the cylinder. so you may end up with  7* (hypothetically speaking here).

youll need to take the window floor down to the desired height and also grind down the floor inside of the tunell to bring it back to 15* if that makes sense. i use paperclips to check the angle then measure that with a instriment that has a degree wheel thing on it. maybe theres a better way but thats how ive always done it

[Bowtie316]

Makes sense, I'll keep that in mind when I start cutting. Thanks for the help.

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[C-Leigh Racing]

I apologize I did not see this in your first post. All cylinder 85-89 are the same dimensionally. The pin height changed from 86 to 87. So it comes down to which piston you are using not the difference in a long or short rod. My builder Pete at Hybrid said he commonly runs the piston out the top and cuts the head to correct the squish.

Having the cylinder as low as you can mount it on the cases & then running the piston out of the deck is the simple way to do it, not the proper way as some will say, but theres been so many strokers built that way I lost count.
One thing that will be a problem, if any port work at all has been done to the cylinder your intending to use.
All porting work will raise the roofs of the ports when completed & if you add a stroker crank into the mix with an already ported cylinder, it will turn the cylinder & engine build into a drag type engine, because of the high port degree openings, so you want a cylinder that the ports have not been touched & then do the cylinder porting after the stroker is added.
Another thing you need to check for, if you go with the cylinder mounted to the cases with one base gasket, so it will be as low as you can get the port windows.
That +4 stroker will add 2 more mm of travel of the piston at TDC, so you'll need to check the piston skirt on the exhaust side while at TDC to make sure the piston skirt not uncovering the floor of the exhaust port.


I dont know if any of you seen the thread on .net where Rob was building one of the 200 engines, but in that thread it was showing pics where the exhaust port floor had been welded on to raise the floor at the edge of the bore, then machined to the proper floor height, so that the piston skirt wouldnt uncover the exhaust port floor while the piston was at TDC. Just saying so you get an idea of what 'm saying.

My deal is, I've never had something new to work on, has been 90% of the time been something somebody else has done & then I had to correct it so it would perform to the customers level, so I've seen a lot of different types of engine combos & had to walk backwards through how it was engineered. I guess you could say I've been through a school of hard knocks figuring out a lot of builders engines.
A Sparks engine is the most mind blowing of all & if you try to change it in any direction, high or low, you'll end up carving into a coolant jacket.
Ol Curtis is smart now, but you take a man that going through life has had to take nothing & make something out of it, he'll dig until he figures it out.

Once you've got the cylinder placement figured out, I would say find a cool head & get a custom dome machined for it or either a CR250R head & have the dome on it machined so the piston can run up into the heads squish area.
The CR head is thicker die cast, will have the OEM TRX look, so the dome area can be machined on it more than a standard cool head type dome.
Cool head dome has cooling fins machined on its outsides, so if you go to carving on the squish area to much you'll end up killing it, reason I say get a custom dome machined.
What would be nice, one of the ESR heads with the stud pattern to match the OEM jug & then a blank dome to machine on to get the proper squish.
Neil

[Bowtie316]

Having the cylinder as low as you can mount it on the cases & then running the piston out of the deck is the simple way to do it, not the proper way as some will say, but theres been so many strokers built that way I lost count.
One thing that will be a problem, if any port work at all has been done to the cylinder your intending to use.
All porting work will raise the roofs of the ports when completed & if you add a stroker crank into the mix with an already ported cylinder, it will turn the cylinder & engine build into a drag type engine, because of the high port degree openings, so you want a cylinder that the ports have not been touched & then do the cylinder porting after the stroker is added.
Another thing you need to check for, if you go with the cylinder mounted to the cases with one base gasket, so it will be as low as you can get the port windows.
That +4 stroker will add 2 more mm of travel of the piston at TDC, so you'll need to check the piston skirt on the exhaust side while at TDC to make sure the piston skirt not uncovering the floor of the exhaust port.


I dont know if any of you seen the thread on .net where Rob was building one of the 200 engines, but in that thread it was showing pics where the exhaust port floor had been welded on to raise the floor at the edge of the bore, then machined to the proper floor height, so that the piston skirt wouldnt uncover the exhaust port floor while the piston was at TDC. Just saying so you get an idea of what 'm saying.

My deal is, I've never had something new to work on, has been 90% of the time been something somebody else has done & then I had to correct it so it would perform to the customers level, so I've seen a lot of different types of engine combos & had to walk backwards through how it was engineered. I guess you could say I've been through a school of hard knocks figuring out a lot of builders engines.
A Sparks engine is the most mind blowing of all & if you try to change it in any direction, high or low, you'll end up carving into a coolant jacket.
Ol Curtis is smart now, but you take a man that going through life has had to take nothing & make something out of it, he'll dig until he figures it out.

Once you've got the cylinder placement figured out, I would say find a cool head & get a custom dome machined for it or either a CR250R head & have the dome on it machined so the piston can run up into the heads squish area.
The CR head is thicker die cast, will have the OEM TRX look, so the dome area can be machined on it more than a standard cool head type dome.
Cool head dome has cooling fins machined on its outsides, so if you go to carving on the squish area to much you'll end up killing it, reason I say get a custom dome machined.
What would be nice, one of the ESR heads with the stud pattern to match the OEM jug & then a blank dome to machine on to get the proper squish.
Neil

Thanks for posting Neil, you brought up something I hadn't thought of, the exhaust port floor being uncovered.  I just went out and checked and it would be by around 1mm if I went ahead and cut the port floor down to the top of the piston.  Is 1mm bad enough to cause a problem? Would it be better just to leave the port floor a tad above the piston to keep this from happening?  I added a second base gasket and that would make it much closer to flush.

This cylinder is totally stock, untouched, no porting whatsoever. The reason I started setting it up so low was because I didn't want the transfer port timing to be too high.  With 2 base gaskets, its already up to 126 degrees.  I was really shooting for 124 degrees and I get that if I use just one gasket.

I have another cylinder I might try, to see if the timing is different.  Again thanks for all the help, this is more about me learning and understanding than anything.

[Bowtie316]

Checked another stock cylinder, this one has a smaller bore at 66.75mm and had just a tad higher port timing with a single base gasket at 182 exhaust and 125 on the transfer. I assume the additional timing is from the angle of the ports in relation to the bore size.

Exhaust port to bottom of the piston is basically the same. Squish with my cool head and a stock gasket was .034 so that's a bit tight but I might just try to add a cr gasket or another base gasket eventually.

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[udontknowme]

if the bore gets bigger the timings should get shorter because of the upward angle of all the ports.

ive noticed the cylinders dont seem to be real consistent in regard to the sleeve matching the cylinder casting or portiming consistency between cylinders. i think they just throw a sleeve in there and machine down the top deck, where the windows end up is where they end up. if theres any large mismatch between sleeve window and casting they do a quick pass with a small grinder and push it out the door. some of the cr500 stuff is pretty ruff looking. for this reason ill bet you can take 2 stock jugs with stock bore and theres good chance theyll have different timings. thats the problem i was having on the 500 stuff

[C-Leigh Racing]

Thanks for posting Neil, you brought up something I hadn't thought of, the exhaust port floor being uncovered.  I just went out and checked and it would be by around 1mm if I went ahead and cut the port flow down to the top of the piston.  Is 1mm bad enough to cause a problem? Would it be better just to leave the port a tad above the piston to keep this from happening?  I added a second base gasket and that would make it much closer to flush.

This cylinder is totally stock, untouched, no porting whatsoever. The reason I started setting it up so low was because I didn't want the transfer port timing to be too high.  With 2 base gaskets, its already up to 126 degrees.  I was really shooting for 124 degrees and I get that if I use just one gasket.

I have another cylinder I might try, to see if the timing is different.  Again thanks for all the help, this is more about me learning and understanding than anything.

You saying when the pistons at BDC, the edge of the piston is lower than the floor of the exhaust port.
Depending on how much lower the piston is to the floor, it probably wont be a problem. When a piston is lower like that, the piston will be almost completely out of the exhaust flow & will tend to cool that part of the piston, not a great deal, but some.
The 0.034 squish is a bit tight, but compression test will tell you a lot. With the lower exhaust timing, you'll need to check how much your traping so the compression wont run up so high. Around 220~240 lbs compression, would make a good low rpm grunt engine, one that would be easy to handle racing.
Neil

[Bowtie316]

You saying when the pistons at BDC, the edge of the piston is lower than the floor of the exhaust port.

Exactly, sorry my wording was a little off, I edited it.

Depending on how much lower the piston is to the floor, it probably wont be a problem. When a piston is lower like that, the piston will be almost completely out of the exhaust flow & will tend to cool that part of the piston, not a great deal, but some.

I would guess the top of the piston is almost exactly 2mm below the exhaust port floor at BDC.  I might be able to lower it some and still keep it covered at TDC, if I can I will.

The 0.034 squish is a bit tight, but compression test will tell you a lot.

Yeah the squish could change since I'm just using feeler gauges to space everything out, 0.020" for the base gasket and 0.055" (1.4mm) on the head gasket.  I will adjust head gasket if I can to get .040-.050" squish, if I can't do it with a gasket I will have to have a dome cut.

With the lower exhaust timing, you'll need to check how much your traping so the compression wont run up so high. Around 220~240 lbs compression, would make a good low rpm grunt engine, one that would be easy to handle racing.
Neil

Yeah I assume with the lower exhaust timing the compression will be high.  I crunched some numbers using UCCR data I have on this cylinder and head combo with the stock stroke and extrapolating what it would be with the increased stroke, I came up with 14.6 UCCR, but I will have to assemble and check it to be certain.

Around 220~240 lbs compression, would make a good low rpm grunt engine, one that would be easy to handle racing.
Neil

I'm not a racer, but I'd sure like to have one that pulls hard but it easy to handle.   Thanks again for the help. I'm hoping to have some time to start cutting on this thing this weekend.

[Bowtie316]

if the bore gets bigger the timings should get shorter because of the upward angle of all the ports.

Yeah that's exactly how this worked out.

I've noticed the cylinders dont seem to be real consistent in regard to the sleeve matching the cylinder casting or portiming consistency between cylinders. i think they just throw a sleeve in there and machine down the top deck, where the windows end up is where they end up. if theres any large mismatch between sleeve window and casting they do a quick pass with a small grinder and push it out the door. some of the cr500 stuff is pretty ruff looking. for this reason ill bet you can take 2 stock jugs with stock bore and theres good chance theyll have different timings. thats the problem i was having on the 500 stuff

Port matching on both of these cylinders are junk, basically they just slapped the sleeve in the cast cylinder and left alone, no touch up whatsoever.  My porting, if you can even call it that, is just to put the exhaust timing where I want it and clean up the casting flash/port matching.  I was planning to open up the boyesen port some.  Hopefully leave everything where it can get a real port job later if this seems like it's going to work out for me.