Hey all

Im currently racing an MC21sp. Its got a HRC loom fitted,JHA pipes,HRCderestrictor and running 195/190 jets. About 2weeks ago I siezed it going down the main straight in practise. This is not the first time though and its always just a matter of time before it goes POP! My last sieze made a hole in the botton piston and blew the hole top of the spark plug away. The funny thing about it all was that the temp was only 70degrees and it happened on the 4th lap. I've bought a new PGMIII box a thew months ago(thinking it was causing detonation on the pistons) but my probs are still not solved. Im also running Wiseco RM125 GP pistons with the barrels skimmed for the correct clearance. I checked the top piston and it looks perfect???? Any help would be greatly appreciated.

Thx a ton

Try a Forum search for "detonation".

I'll go out on a limb here and say "put a 0.6mm base gasket on the lower cylinder".
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Andy.
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Andy....what difference will this base gasket make?
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Hmmmmm!

depending on what is on there, it will either increase, or decrease compression/deck height.

since 0.6 is generally the thickest one from Honda, it will decrease your compression. What the thicker base gasket will do is raise the cylinder, pushing the head further away from the top of the piston at TDC, lowering the compression of the cylinder (the tighter the deck height, the more compression).

generally on the NSR, I don't worry about this level of tuning. However on the RS I will measure the base gasket thickness (I have a stack of about 50 or more of them), I will measure the cylinder height, as well as measure the height of the piston (again, have six or seven of these) to get the right match to make the proper compression on each cylinder.

After I put it all together, I then measure the deck height to make sure my seperate measurements all were done properly.

of course with a set of VHM heads, you can change the compression with different inserts, adding one more variable to the puzzle

Thanks,
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Charles Gallant


Last edited by cgallant on Tue May 24, 2005 10:51 pm; edited 1 time in total

DMB wrote:Andy....what difference will this base gasket make?

Probably (well, possibly) enough to stop destroying lower cylinders with an HRC head conversion and crap fuel!
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Andy.
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Fuel, it's gotta be crap fuel that kills them.

Feed it the good stuff....
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These aren't the droids you're looking for.

Just been through all this on another thread!
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Andy.
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That's the beauty of threads, they differ so much even though the subject may, on occasion, be the same.

It's for that reason I think it's bad form to say - 'see this thread' or 'do a search' as an all encapsulating reply..... as to encourage 'discussion' in a 'Discussion forum' means that the potential for further analysis and examination of an issue is allowed - suggesting that the potential for a better understanding of the situation can exist which is a sign of a need to understand more and a desire to progress.

That in itself is what it's all about ?

Discuss.........
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These aren't the droids you're looking for.

I think it often shows laziness and lack of willing to do some research on an already covered topic.

Very rarely do we see a first-time poster say "I've thoroughly searched the Forum, but can't find a suitable answer..." and with over 8000 articles now, many of the common issues have been discussed already.

I'd rather see an old topic "bumped" back to the top of the list as it keeps the information more readily available and easier to find. Continually starting topics on similar issues just fragments the information, making it harder to correlate.

At the end of the day, I and many of the other contributors have not only put time into our research, but put YEARS into it, and then gone to the effort of making it readily available to others. I don't think it's asking much to do a little research before asking. Hell, one of two recent topics discussing detonation and lower cylinder destruction is actually still on the first page of the Discussion Forum and has 31 posts!
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Andy.
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Thx for help. Will try the gasket. I think im still using the stock gaskets. Btw....I did a search regarding my topic but there were way to many things that came up and most of the members bikes were differently set up to mine....(so no laziness, just not sure)The thing i couldnt understand is how the plug chop can give a good reading but the bike still ends up siezing. Hopefully the gasket will solve all my isues. Getting new pitons too. Cant wait!

Thx again

It's not "having a go at Brollocks" day, don't worry, more of a return volley to Binka. I stand by what I said, as although not exactly the same issue (maybe because of setup like you say) but it is a similar symptom, so adding further to one of the previous threads I feel would have been valid.

My problem is I often have too much to say so tend to add it all in to one post when it's time to moderate a little. I'd rather make my point of view and feelings known outright, than snipe or whinge behind peoples backs! At least everyone knows where they stand then!

Hope there is some useful information or ideas here anyway, and best of luck.
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Andy.
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Andy!!!! If a thicker gasket is fitted, this will alter the port timings as well as lower the compression. So both cylinders will have to have the same thickness gasket? Would you then have to reset the exhaust valve cables to suit?
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Hmmmmm!

a thicker base gasket will alter the port timing a little, but will not alter the exhast valve.

Andy wrote:It's not "having a go at Brollocks" day, don't worry, more of a return volley to Binka. I stand by what I said, as although not exactly the same issue (maybe because of setup like you say) but it is a similar symptom, so adding further to one of the previous threads I feel would have been valid.

My problem is I often have too much to say so tend to add it all in to one post when it's time to moderate a little. I'd rather make my point of view and feelings known outright, than snipe or whinge behind peoples backs! At least everyone knows where they stand then!

Hope there is some useful information or ideas here anyway, and best of luck.

There's a good point there - if you ask anyone who uses a php board and ask about searches, the answer is usually the same. Too many responses and too much rubbish.

Hence, what most people do is look down the first two or three pages and if there's nothing relevant, post a question.

The only bad question is an unasked question. The quality of the reply is where it can all fall down and Andy knows exactly what my take on that is.
I'd do anything for anyone provided it was a. legal and b. reasonable.
Just to be clear, I'm deffo not having a go at anyone, no need for that here as the majority are beyond that crudd.

Jacking up the barrels to give you more clearance in the squish is a really, really bad way to do this. It goes against every principal of 2 stroke tuning. Yes, it will change the port timings and squish. As noted by Howard Lees back in 1986 (PB) and echoed by just about every top stroker tuner, if you are jacking up the barrels you should really be doing this for 1 reason and that is because you screwed up the milling on the head or barrel deck. It is a common problem these days on old 350lc engines running a 375cc kit. The original 375cc conversion using DT175mx jugs required the barrel to be shortened and a mix and match of base gaskets were needed to take up bad machining or very small inaccuracies. This led to a lot of early engine deaths because people who didn't really appreciate how crittical it all is, had a go themselves and is the main reason why so few 375cc kits using the DT piston remain. They all blew up !
If I were looking at this problem I'd be looking at a meticulous check of the crank timing, ignition timing and carefully measure the chamber volume and squish. If all checked out ok when the maths and numbers were crunched then I'd leave the thin base gasket in there and use a detonation ring in the heads and use nothing but 4 star juice.
The 76rwhp YPVS runs a very tight squish, it has never misbehaved because the fuel is right for the ignition and compression inspite of my running some things that most people cringe at the idea of.



There's definately an issue with the lowe cylinder of NSR's curling up and dying.... closer analysis is needed me reckons.
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These aren't the droids you're looking for.

It's no big issue Binka, simple a case of HRC knowing of a "trick" to make the lower cylinder more efficient and keeping things within the SP rules, and others with less knowhow following suit.

If the stock head is kept, the NSR is as reliable as the day is long - a hell of a lot more reliable that an old steel linered RD, that's for sure!

The use of the HRC head should be used in conjunction with 105 octane race fuel, HRC specifically state this, but running that fuel is beyone the practicality of most road riders. For this reason, the big Japanese tuners, and a few well informed individuals, have opted to use the 0.6mm HRC base gasket as a tiny safety margin against the possibility of detonation due to the fact that machining barrel and/or head surfaces was illegal in most race series, and again beyond the practicality of most road riders.

0.1mm is hardly going to shatter the performance figures and port statistics of an NSR motor, but it will most probably help prevent the destruction of a barrel.
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Andy.
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